Posted on September 2, 2019
Kennedy W. Nyongesa1, Francis O. Obiria2, Bernard S. Omuya2
1 Institute for Climate Change and Adaptation (ICCA), University of Nairobi
2 Kisii University
Agriculture is extremely vulnerable to climate change. Increased temperature eventually reduces yields of desirable crops while promoting weed infestation and proliferation of pest. Decline in precipitation increase the likelihood of crop failures and exacerbate food insecurity. Although there could be gains in some crops in some regions of the world, the overall impacts of climate change on the Agro-ecosystems are expected to be negative, threatening food security. The continued dependence of crop production on light, heat, water and other ecological and climatic factors warrants the need for a comprehensive consideration of the potential impacts of climate on global agriculture. Tropics are more dependent on agriculture compared to the temperate regions and therefore more valuable to climate change. Hydrological regimes in which crops grow will surely change with global warming; climate change will also have an impact on the soil, a vital element in agricultural ecosystems. Higher temperatures will increase evapotranspiration and soil temperatures which increase chemical reactions rates and diffusion controlled reactions. While crops could be impacted by climate change, it is likely that farm animals would will be ever more susceptible to change in climate. It is expected that increased air temperatures will cause more heat stress to livestock. Livestock are endodermic hence they are affected by increased heat and humidity. During stifling heat livestock reproduction declines as well as appetite due to hormonal changes. Decreased appetite will lengthen the time needed for livestock to reach their target weight. Heat stress can also increase fighting among animals. This theoretical review paper encapsulates these concepts in conceptual framework. A conclusion is drawn illustrated by a conclusive working model.
Key Words: Climate Change, Agro-Ecosystems, Agriculture, Food Security
Agro-ecosystems are ecological systems modified by human beings in order to produce food or other agricultural products (Conway, 1987). The agro-ecosystems in the Highveld region of South Africa produce 70% of the country’s commercially grown cereal crops, with 90% of its maize being cultivated there (du Toit et al., 2000). The sustainability of the maize producing agro-ecosystems is of huge consequence to food security in South Africa and to the well-being of the rural economy of the Highveld. Chambers (1997) recognizes that humans are at the centre of agro-ecosystems and that their well-being is a key issue for the sustainability of agro-ecosystems. Sustainability is applying long term perspectives, in regard to human well-being and ecological integrity, to policies and actions. (Walker and Schulze, 2006). This definition of sustainability is used by the authors in this paper. The sustainability of agro-ecosystems in Africa will be influenced, inter alia by climate change and by land use changes and related factors resulting from the above two (Hansen and Jones, 1996).
The inter-relationships between social, economic and environmental influences are associated with sustainability, a systems approach to sustainability is therefore essential (Ikerd, 1993). For such a systems approach, a framework was adapted with a goal-orientated system. Incorporating Hansen and Jones (1996) method to characterize sustainability, the framework has the following four steps: 1. Goal definition; 2. Sustainability modeling; 3. Evaluation strategy and 4. Making recommendations that are predictive, with constraints to sustainability being identified. Hansen (1996) considers it necessary to characterize the concept of sustainability when using it to identify constraints, to identify research foci and for policy development. A case in point is the influence of El Nin˜o on the seasonal rainfall in the Highveld region in South Africa, a reality for farmers (du Toit and Prinsloo, 1998), since it influences directly both their economic security in the long term and local food security in the shorter term.
Linkage between Agro-ecosystems, Land use Changes and Climate Change
Olson et al. (2004) observe that expansion of cultivation in many parts of East Africa has changed land cover to more agro-ecosystems; food production in Kenya, for example, is reported to have increased steadily between 1980 and 1990. In East Africa, natural vegetation cover has given way not only to cropland, native or planted pasture.
Further, Olson et al. (2004) posit that land use changes in East Africa has also experienced the expansion of urban centers and urban population between 1960 and 2000; during the last few decades the area under cultivation more than doubled in Kenya and Tanzania, but in Uganda the change has been moderate. In Mbeere, in Kenya cultivation expanded by 70% between 1958 and 2001, leaving only isolated pockets of forest and bush. Similarly, in Tanzania, report a significant expansion of cultivation in the Moshi area over the same period. However, in Uganda, agriculture only expanded in the drier rangelands, not in the wetter highlands.
Globally, there was realization that land surface processes influence climate and that change in these processes impact on ecosystem goods and services (Antrop, 2000). The impacts that have been of primary concern are the effects of land use changes on biodiversity, soil degradation and the ability of ecosystems to support human needs (Alcamo, et al., 2005). The sequence of land cover and land use change in East Africa is complex (Mugisha, 2002). In some places pastoralists modify wooded landscapes into more open landscapes by burning, the changes are quite subtle and pastures can quickly revert to bush land and woodland when burning ceases (Olson et al., 2004).
Campbell et al. (2003) observe that land use changes and climate variations influence each other. Numerous studies have shown that land use changes and climate variations affected the structure and function of ecosystems and then affected the supply of ecosystem services (Olson et al., 2004). Land use changes might increase provision and value of some services but decrease others (Antrop, 2000). The effects of land use changes and climate variations may increase changes in ecosystem services delivery (Alcamo, et al., 2005). As to the impacts of climate variations on human wellbeing, it can aggravate the situation for food security by increasing risks of crop failure because of the higher frequency of extreme events and progressive changes of climate (Sivakumar and Brunini, 2005). In addition, as some ecosystem services decline, some new human actions, such as the excessive use of fertilizers and pesticides, have had adverse impacts on ecosystems and further on human wellbeing (Power, 2010, McCarthy et al., 2001).
Hydrological Regimes, Climate Change, Water Security and Food Security
Hydrological regime refers to changes with time and space in rates of flow of rivers and in levels and volumes of water in rivers, lakes, reservoirs marshes and other water bodies. A hydrological regime is closely related to seasonal changes in climate (Cowx, 2000). In regions with a warm climate, the hydrological regime is affected mainly by atmospheric precipitation and evaporation; in regions with a cold or temperate climate, the air temperature is a leading factor (Nilsson and Berggren, 2000).
The hydrological regime of rivers consists of a number of characteristic periods (phases) that vary with seasonal changes in the conditions under which rivers are fed (Nilsson and Berggren, 2000). These phases are known as high water, freshet, and low water. Rivers are fed unevenly in the course of a year because of varying amounts of precipitation and uneven melting of snow and ice and entry of their water into the rivers (Cowx, 2000). The fluctuations observed in the water level are caused mainly by changes in the flow rate and by the effects of wind, ice, and man’s economic activities (Kundzewicz et al., 2007).
Cowx, 2000 posits that the hydrological regime of lakes is determined by the relationship between the amount of precipitation reaching the lake’s surface, evaporation, surface and underground flow into the lake, and surface and underground outflow of water from the lake, as well as by the size and shape of the lake, the pattern of change in the surface area with change in level, and wind activity, which determines the size of the waves and the extent to which the level rises and falls. Kundzewicz et al., 2007 conclude that the hydrological regime of marshes is dependent on climatic and hydrological conditions, terrain, and the nature of the vegetation. Nilsson and Berggren (2000) observe that man’s economic activities are introducing ever greater changes in hydrological regimes.
The impact of climate change on the quantity and quality of groundwater resources is of global importance because 1.5–3 billion people rely on groundwater as a drinking water source (Kundzewicz and Döll, 2009). There has been very little research on the impact of climate change on groundwater (Kundzewicz et al., 2007). Studies of Global Climate Models (GCMs) projects significant changes to regional and globally averaged precipitation and air temperature, and these changes will likely have associated impacts on groundwater recharge (Kurylyk and MacQuarrie, 2013). Studies show that agricultural yield will likely be severely affected over the next hundred years due to unprecedented rates of changes in the climate system (Jarvis et al., 2010; Thornton et al., 2011). In arid and semi-arid areas the expected precipitation decreases over the next century would be 20% or more.
According to UNEP (2004), the world experienced unprecedented high-impact climate extremes during the 2001–2010 decade that was the warmest since the start of modern measurements in 1850. In 1955, only seven countries were found to be with water stressed conditions. In 1990 this number rose to 20 and it is expected that by the year 2025 another 10–15 countries shall be added to this list. It is further predicted that by 2050, 2/3rds of the world population may face water stressed conditions (Gosain et al., 2006); majority of the Arab countries depend on the international water bodies for their requirements.
UNESCO (2004) reports that the Nile river basin is the home of approximately 190 million people of Ethiopia, Eritrea, Uganda, Rwanda, Burundi, Congo, Tanzania, Kanya, Sudan and Egypt. Since majority of nations of the Nile river basin are among the top 10 poorest countries of the world therefore it is absolutely difficult for them to adopt any strategy of water management, which require investment. The OSS (Observatory of the Sahara and the Sahel) regions, which have the least natural water resources, both in absolute terms and in relation to its population will be affected severely. Over 90% of Sub-Saharan Africa agriculture is rain-fed, and mainly under smallholder management (Batino et al., 2011). de Wit and Stankiewicz (2006) identify three river systems in Africa: the areas receiving very low rainfall have virtually no perennial drainage (dry regime), then the areas with an intermediate range in which drainage density increases with increasing rainfall (intermediate rainfall regime) and the areas of high rainfall (high rainfall regime). The dry regime covers the largest area of the African continent, approximately 41%; the intermediate rainfall regime which covers approximately 25% because this is the area where changes to precipitation would result in serious changes in drainage supply. Further, as predicted by an ensemble of global climate change models by the second part of this century, climate change would directly affect African countries, 75% of which belongs to the intermediate stage. Fig. 1 shows the present rainfall regimes in Africa and Fig. 2 shows the expected changes in the precipitation by the end of the 21st century on the basis of composite leading fully coupled GCMs adapted by IPCC for forecasting purposes (CSAG, 2002). A net 2.5 °C rise in temperature in Africa will result in a decline of net revenues from agriculture by US$ 23 billion (Kurukulasuriya and Mendelson, 2007).
Fig1: Precipitation in the African continent at the end of 20th century
Source: de Wit and Stankiewicz, 2006
Fig 2: Predicted changes in the precipitation in the African continent due to climate change at the end of the 21st century
Source: de Wit and Stankiewicz, 2006).
The shortage of water can be augmented from wastewater utilization after suitable treatment (FAO, 2012). Water recycling by giving technological support can speed up can help in minimizing the impact of climate change on crop yield and water resources (de Wit and Stankiewicz (2006).
The Relationships between Soils, Climate Change and Food Security
Soils are important to food security and climate change has the potential to threaten food security through its effects on soil properties and processes (Brevik, 2012). It requires an understanding of how climate and soils interact and how changes in climate will lead to corresponding changes in soil (Pimentel, 2006). Respective of soils and climate change interactions are the carbon and nitrogen cycles because C and N are important components of soil organic matter (Brady and Weil, 2008); because carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the most important of the long-lived greenhouse gases (Hansen, 2002). Human management of soils can have a profound impact on the balance of C and N gas emissions from those soils, and therefore influences global climate change (Post et al., 2004).
The largest active terrestrial C pool is in soil, which contains an estimated 2,500 Pg of C compared to 620 Pg of C in terrestrial biota and detritus and 780 Pg of C in the atmosphere (Lal, 2010). Carbon is readily exchanged between these pools; therefore, they are called active pools. In addition to the active pools, there are approximately 90,000,000 Pg of C in the geological formations of Earth’s crust, 38,000 Pg of C in the ocean as dissolved carbonates, 10,000 Pg of C sequestered as gas hydrates, and 4,000 Pg of C in fossil fuels (Pimentel,2006). However, most of the C in these pools is locked up over long periods of geologic time and not readily exchanged; leading to these pools being referred to as inactive pools (Post et al., 2004); the release of C from the inactive pools, particularly though the combustion of fossil fuels is also an important anthropogenic source of greenhouse gases. Soils naturally sequester C through the soil-plant system as plants photosynthesize and then add dead tissues to the soil (Post and Kwon, 2000). Carbon is also naturally emitted from soils as CO2, CO and CH4 gases due to microbial respiration (Brady and Weil, 2008). Soil management techniques such as no-till systems may result in lower CO2 emissions from the soil and greater C sequestration in the soil as compared to management systems based on intensive tillage (Brevik, 2012).
However, other management changes such as using cover crops, crop rotations instead of monocropping, and reducing or eliminating fallow periods can lead to C sequestration in soil; as can returning land from agricultural use to native forest or grassland(Brevik, 2012). Sequestration of C tends to be rapid initially with declining rates over time (Dixon-Coppage et al., 2010). Most agricultural soils will only sequester C for about 50–150 years following management changes before they reach C saturation (Mosier, 1998).
The C and N cycles are key parts of the global climate system, and soils are an integral part of these cycles (Post and Kwon, 2000). Agriculture contributes a particularly large percentage of annual anthropogenic CH4 emissions to the atmosphere (Mosier, 1998). Agriculture contributes CO2, CH4, and N2O into the atmosphere; hence management systems have the potential to influence climate change (Dixon-Coppage et al., 2010). The interactions between soils and the atmosphere in a changing climate are important variables as we seek to understand climate change and its potential influence on food security through the biogeochemical cycles (Pimentel, 2006).
Food systems, Food security and the link to Climate Change
Food security depends on robust food systems that encompass issues of availability, access and utilization, not production alone and consequently that the nature of key research issues changes as more questions related to food security are formulated (Ingram et al., 2005). There are several definitions of what constitutes food systems each formulated in relation to a specific range of issues such as globalization of the agri-food systems (Goodman, 1997); community food systems (Gillespie and Gillespie ,2000); ecological interests (Barling, 2004).
Ingram et al. (2005) posits that food systems are defined as a set of dynamic interactions between and within the biogeophysical and human environments which result in the production, processing, distribution, preparation and consumption of food. They encompass components of: (i) food availability; (ii) food access and (iii) food utilization.
Access to culturally acceptable food Food systems may be simple, as in the case of a subsistence farmer who produces processes and consumes food on farm. Ingram et al. (2005) conclude that intensification of agricultural production, since the 1940s has been accompanied by profound changes in the organization of food systems around the world including changes in distribution, marketing, affordability and preferences for particular food items.
Food systems around the world are changing very rapidly as urbanization and globalization proceeds apace (Ingram et al., 2005). The urbanization of many predominantly rural countries in the last three decades has been accompanied by the rapid growth of supermarkets in many countries, often accompanied by foreign investment by global retail chains (Reardon et al., 2003). However, even in African countries such as Kenya, supermarkets have grown from a tiny niche market in 1997 to be greater than 20% of urban food retailing today (Neven and Reardon, 2004). Success within Kenya is now spreading to other East African countries with important effects on the market conditions faced by farmers including the decline of traditional wholesalers and the increase in direct purchases from larger farms. Table 1 shows changes in the supply of fresh fruit and vegetables to the Uchumi supermarket chain in Kenya by supplier type for the period 1997–2008.
Table 1: Changes in the supply of fresh fruit and vegetables to the Uchumi supermarket chain in Kenya by supplier type for the period 1997–2008.
|Type of supplier||Vegetables||Fruits|
|large farms and plantations||5||15||35||0||15||35|
The values are the percentage contribution to the total supply.
Source: Neven and Reardon, 2004.
According to Gregory and Ingram (2000), climate change may affect food systems in several ways ranging from direct effects on crop production to changes in markets, food prices and supply chain infrastructure. For example in southern Africa, climate is among the most frequently cited drivers of food insecurity because it acts both as an underlying, ongoing issue and as a short-lived shock. Because of the multiple socioeconomic and biophysical factors affecting food systems and hence food security, the capacity to adapt food systems to reduce their vulnerability to climate change is not uniform across regions (Jones and Thornton, 2003). Several reviews have further assessed the potential consequences of changes in climate on the growth and yield of crop plants (Amthor, 2001); their linkage to plant physiological processes hence concluding that the earlier-anticipated benefits of C02 fertilization would be largely offset by nutrient limitations, pollutants and further interactions with climatic factors (Long et al., 2005). This, and other similar projections that use a process-based crop production model to link climate change to crop yield can then be modeled for a uniform crop yield and up scaled to a larger area normally within some form of geographic information system (GIS). Figure 3 shows the three components of food systems with their main elements.
Figure 3: The Three Components of Food Systems with their Main Elements Source: Gregory and Ingram, 2000.
Misselhorn (2005) observes that, to better address the food security concerns that are central to economic and sustainable development agendas, it is desirable to develop a broader research framework, which integrates biophysical and socio-economic aspects of food systems and thereby addressing two key questions:
(i)Which aspects of food systems are most vulnerable to climate change?
(ii) What can be done to reduce the vulnerability of
these food systems and thereby improve food
In studies of household food security in southern Africa, climate was one of some 33 drivers mentioned as important by householders (Misselhorn, 2005). It has become clear that the key to assessing vulnerability is to develop research frame-works which can explicitly consider the social and political constraints which condition the capacity of food systems to cope with external stressors such as climatic change (Mustafa, 1998). Finally, changes in the food systems aimed at reducing vulnerability feedback to environmental and societal changes themselves may reinforce agricultural practices that either reduce or exacerbate land degradation, and increase or reduce farm profitability (Adger, 1999; Scholes and Biggs, 2004). According to Gregory and Ingram (2000) not all food systems are equally vulnerable to environmental changes. Human vulnerability and poverty are often interrelated because both the likelihood of exposure to stresses is greater among the poor and because a large proportion of their resources are spent either purchasing or producing food, thereby reducing their capacity to cope with perturbations (Hume et al., 2001). Regional policy decisions do not always convert to successful local implementation especially if distribution services are inadequate, or food preferences are ignored (Ellis, 2003). The following adaptation actions are illustrated below using an example from each of the three elements of the food system as depicted in figure 1. (a) Reducing food system vulnerability by increasing food production: Past increases in agricultural production have occurred as a result of both extensification (altering natural ecosystems to generate products) and intensification (producing more of the desired products per unit area of land already used for agriculture (Gregory and Ingram, 2000). In future, intensification will be the dominant means for increasing production although the cultivation of new land will be important in some regions (e.g. an estimated contribution of 47% from extensification in sub-Saharan Africa to cereal production by 2020 (Alexandratos, 1995). (b) Reducing food system vulnerability by improving food distribution: Pingali and Khawaja (2004) assert that infrastructural and non-infrastructural controls on food distribution can be significant impediments to reducing food system vulnerability in a timely manner. This became strikingly apparent during the drought relief effort mounted in 1990/1991 in southern Africa in response to the estimated 86 million people at risk in the region of whom some 20 million were deemed at serious risk. Food availability for the region was severely constrained due not to lack of food per se but by lack of investment in distribution systems and institutional constraints. This brief summary highlights several ways in which regional food insecurity could be reduced, and shows that adaptation options caninclude arange of issues including, among others, regional investment in port, rail and grain storage infrastructure and in region-wide political agreements to facilitate the flow of food in an emergency. (c) Reducing food system vulnerability by increasing economic access to food: In the case ofsouthern Africa, Arfitzen et al. (2004) indicates that the discussioncenters on varied means. According to Mahendra Dev et al. (2004); first, price mechanisms and policies could be designed that serve the interest of producers and consumers. Second, regional specialization in food production and regional trade would lower production costs and food prices and, therefore, improve access. Third, economic growth will lead to income and employment generation, both of which will facilitate access to food. Finally, stability in political governance supported by an effective pool of human and institutional resources facilitates the establishment and maintenance of food systems. Figure 4 shows the conceptual framework as envisaged in this review, depicting the main drivers of Food Insecurity in Africa. This conceptual framework can be adopted for research.
Figure 4: The Conceptual Framework that shows that the Interrelationships between the Aspects that Determine Food Insecurity.
Source: Nyongesa, Obiria and Omuya, 2017
Agro-ecosystems may be strongly influenced by projected increase in atmospheric CO2 concentration and associated climate change (Reilly, et al., 1996). The direct effect of increasing CO2 concentration on plant growth is of particular interest because of the possibility of increasing crop yields in the future once the substrate for photosynthesis and the gradient of CO2 concentration between atmosphere and leaf will increase (Reid, et al., 2005). Current atmospheric CO2 concentration (about 360 µmol mol-1) is insufficient to saturate the ribulose 1, 5-bisphosphate carboxylase (Rubisco), the enzyme responsible for primary carboxylation, the metabolic process that drives photosynthesis, in C3 plants (Sivakumar and Brunini, 2005); very few studies indicate a yield depression at elevated CO2 concentration and those are primarily with flower crops.
Probably the most important physical effect of transpiration in plants is the cooling that takes place at the transpiring surface (Sivakumar and Brunini, 2005). Because large quantities of energy are required in the phase change from liquid to vapor, evaporation provides a very efficient mechanism for heat dissipation.
An Overview of Impacts of Climate Change on Livestock Productivity
Thornton et al. (2007) posit that the situation in Africa and other developing countries is that generally, climate can affect livestock directly and indirectly. Although indirect, feed resources can have a significant impact on livestock productivity, the carrying capacity of rangelands, the buffering ability of ecosystems and their sustainability, and the distribution of livestock diseases and parasites In Africa the main pathways in which climate change can affect the availability of feed resources for livestock are as follows:
1. Land use and system changes can lead to different compositions in animal diets and to alteration in the ability of smallholders to manage feed deficits in the dry season (Thornton et al., 2007).
2. Changes in the primary productivity of crops, forages and rangelands are probably the most visible effect of climate change on feed resources for ruminants with the end result, for livestock production, a change in the quantity of grains, stovers and rangelands available for dry season feeding (Thornton et al., 2007).
3. Changes in species composition in rangelands and some managed grasslands will have significant impact on the types of animal species that can graze them, and may alter the dietary patterns of the communities dependent on them (Thornton et al., 2007).
4. The quality of plant material will be altered (from C3 to C4) by increased temperatures and will reduce the digestibility and the rates of degradation of plant species which will lead to reduced nutrient availability for animals (Thornton et al., 2007).
4. However, increased levels of CO2 may favour C3 plants; it is also possible that C4 grasses may be replaced with C3 grasses owing to increased levels of CO2 (Taub, 2010); or climate change may result in the deterioration of pasture towards lesser quality sub-tropical C4 grasses.
Climatic changes directly influence livestock health through a number of factors, including the range and abundance of vectors and wildlife reservoirs, the survival of pathogens in the environment, and farming practice (Gale et al, 2009; Semenza and Menne, 2009). Transmission of zoonotic diseases occurs when there is an overlap of activities between reservoir, vector and humans; changes in climate may impact on all of these factors involved in disease transmission and interactions (Gray et al, 2008; Randolph, 2008a). Abiotic factors, such as temperature and day length, impose constraints on when and how ticks quest for hosts (Randolph, 2008b). Beyond vector-borne diseases, intestinal nematodes develop in soil, and factors such as soil humidity and temperature have a strong influence on developmental rates (Brooker et al., 2002). Direct effects are also related to radiation, the animal’s inability to dissipate environmental heat causes heat stress (Fuquay, 1981; Bucklin et al., 1992). Evaporation is the most important methods of heat transfer as it does not depend on a temperature gradient (Ingram and Mount, 1975). Humidity affects the evaporation rate; therefore, the temperature humidity index (THI) becomes relevant under conditions of high temperature and high humidity (Thom, 1958).
Compiling and analyzing the results of more than 770 reports about the CO2 enrichment on the economic yield of 24 agricultural crops and 14 other species, Jarvis et al. (2010) showed that only 39 out of 437 separate observations (i.e. 9%) yielded less than their respective controls and the average relative increase was 28% considering all of the crops or 36% excluding flowers. The effect of CO2 enrichment on flower yield was generally lower than on food crops. Mean yield increases were 23%, 32%, 42%, 54% and 52% for fruit, cereal C3, leaf, legume and root crops, respectively. Hansen (2002) estimated that a doubling CO2 concentration, holding other factors constant, could lead to a 34 ± 6% increase in agricultural yields of C3 plants and a 14 ± 11% in C4 plants with a 95% confidence interval. Gregory et al., 2005 concluded that provided adequate water, nutrients and pest control, yields of C3 and C4 crops growing in about 700 µmol CO2 mol-1 would be about 30 to 40% and 9%, greater than present yields, respectively. Below-ground growth is also increased at elevated CO2 concentration
Application: Suggested Adaptation Mechanisms
Food systems, underpin food security, which is the state achieved when food systems operate such that all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life (McClain-Nhlapo, 2004); food security is diminished when food systems are stressed. For the future, continued technological developments are anticipated to facilitate the adaptation of crops to changing environments (Gregory et al., 2005).
There are many plant characters and elements of crop management that contribute to the efficient use of water by crops (Gregory, 2004), but relatively little attention has been paid to root characters that may allow more water to be exploited or used more efficiently, largely because root systems are very difficult to measure. However, genotypic differences are known to exist in many features of root systems which may be exploitable to improve crop yield in drier climates (O’Toole and Bland, 1987). Studies with existing genotypes in dry areas may inform the adaptation possible under conditions of changed climate (Champoux et al., 1995). Porter and Semenov (2005) posit that the development of DNA-based molecular markers has opened up opportunities for identifying the genetic factors (quantitative trait loci) underpinning various root traits. Again, this science is at an early stage of development for root traits, but significant progress has been made in studies of drought tolerance with rice (Babu et al., 2001). In reducing food system vulnerability by increasing economic access to food, this important adaptation is as yet hardly pursued, but should gain momentum with trade liberalization and policy shifts towards food security.
Studies on the impacts of Land use changes and climate variations on ecosystem provisioning services and the impacts of provisioning services changes on human wellbeing will provide scientific and theoretical basis for global policy making especially focusing on food security. At present, our understanding of how changes in climate will influence the C and N cycles is incomplete, meaning additional research into these questions is needed. Notably, it has become necessary now to take very seriously the impact of climate change on the present water resources and take necessary actions without any further delay; because food grows where water flows.
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A Review of Impacts of Global Climate Change on Bioaccumulations and Biomagnifications and the Implications on Human Ecology.
Kennedy W. Nyongesa
Institute of Climate Change and Adaptation (ICCA), University of Nairobi, Corresponding email:firstname.lastname@example.org
This paper reviews information from the literature on impacts of climate change including ecological drought. The paper highlights how climate change affects bioaccumulations, biomagnifications, and the implications on human ecology. Global climate change (GCC) is likely to alter the degree of human exposure to pollutants and the response of human populations to these exposures, meaning that risks of pollutants could change in the future. The paper, therefore, explores how GCC might affect the different steps in the pathway from a chemical source in the environment through to impacts on human health and evaluates the implications for existing risk-assessment and management practices. In certain parts of the world, GCC is predicted to increase the level of exposure of many environmental pollutants due to direct and indirect effects on the use patterns and transport and fate of chemicals. Changes in human behavior will also affect how humans come into contact with contaminated air, water, and food. Dietary changes, psychosocial stress, and co exposure to stressors such as high temperatures are likely to increase the vulnerability of humans to chemicals. These changes are likely to have significant implications for current practices for chemical assessment. Assumptions used in current exposure-assessment models may no longer apply, and existing monitoring methods may not be robust enough to detect adverse episodic changes in exposures. Organizations responsible for the assessment and management of health risks of chemicals therefore need to be more proactive and consider the implications of GCC for their procedures and processes. In this paper, a conclusion is drawn illustrated by a conclusive working model.
Key Words: Impacts, Global Climate Change, Bioaccumulations, Biomagnifications, Human Ecology.
Written records from up to 5 millennia ago provide evidence of climatic impacts on food shortages, famines, starvation, and deaths ; it must be noted that the historical data available for analysis are usually patchy. Often, the records do not associate occurred events with specific climatic conditions or are inherently biased. For example, there is little explicit information about specific population health benefits during benign climatic periods. Rather, the adverse periods and outcomes customarily attract attention and are usually well documented. In addition, information about heat wave impacts in earlier centuries is negligible, although information about deaths and suffering from periods of extreme cold often exists.
However, one must keep in mind that today’s wealthier and technology-rich societies differ in many ways from earlier societies. In several respects, modern societies might be more vulnerable to climatic stress than their predecessors. Potential vulnerabilities of modern societies include increasing deficit of suitable places for resettlement; increasing density of populations in vulnerable locations such as flood-plains and coasts; enhanced spreading of infectious diseases due to urbanization and globalization; fragility of complex urban infrastructure; disruptive changes in the Earth’s biosphere (land and sea overuse, disrupted nitrogen and phosphorus cycles, biodiversity losses); international tensions and economic crises. The nexus of drought, famine, and starvation has been the major serious adverse climatic impact over the past 12,000 years. Cold periods, more frequent and often occurring more abruptly than warm periods, have caused more apparent stress to health, survival, and social stability than the warming. Temperature changes of 1 to 2 °C (whether up or, more frequently, down) can impair food yields and influence infectious disease risks. Hence, the health risks in a future world forecast to undergo human-induced warming of both unprecedented rapidity and magnitude are likely to be great. Figure 1 shows the historical overview of Climate Change.
Figure1: Historical Overview of Climate Change.
Source: National Academy of Sciences
Variations in northern hemisphere temperature, °C (relative to mean temperature during 1960–1980), averaged from multiple sources published since 2007. Averaging of hemispheric temperature is therefore only indicative. During early–mid Holocene (11–4 thousand years before present), for example, trends in regional temperatures differed, including prolonged cooling of much tropical ocean while warming for over 2 millennia in parts of Europe, China, and Scandinavia.
Global-scale Forcing of State Shift in Earth’s biosphere
Biological systems on local as well on global scale can shift rapidly from an existing state to a radically different state. A defined range of deviations from a mean condition over a defined period characterizes biological states. Either a “threshold” or a “sledgehammer” effect can cause this shift from one state to another. The former can be difficult to anticipate, because the critical threshold is reached slowly as incremental changes accumulate and the threshold value generally is not known in advance. By contrast, a state shift caused by a sledgehammer effect – for example the deforestation by logging – comes as no surprise. In both cases, the state shift (critical transition) is relatively abrupt and leads to new mean conditions outside of range of fluctuations observed in the previous state. The net effect is that once a critical transition occurs, it is usually irreversible. Recent theoretical work suggests that state shifts may be preceded by the following phenomena: a deceleration in recovery from perturbations (critical slowing down); an increase in the variance in the pattern of within-state fluctuations (asymmetry in fluctuations, changes in amplitude, etc.); increase in frequency of fluctuations (“flickering”).
Earth’s biosphere has undergone state shifts in the past over various time scales: last glacial-interglacial transition, “Big Five” mass extinctions and Cambrian explosion. One of the fastest planetary state shifts, and the most recent, was the transition from the last glacial (Pleistocene or Quaternary glaciations) into the present interglacial period (Holocene), which occurred over millennia. Glacial conditions had prevailed for ~100,000 years. Then, within approx. 3300 years, punctuated by episodes of abrupt, decadal-scale climatic oscillations, full interglacial conditions were attained. No completely satisfactory theory has been proposed to account for Earth’s history of glaciations. The causes of glaciations and deglaciation may be related to several simultaneously occurring global forcings, such as astronomical cycles, atmospheric composition, plate tectonics, and ocean currents. During last transition, most of the biotic change (extinctions, altered diversity patterns, new community assemblages, etc.) occurred within a period of 1,600 years beginning about 12,900 years ago. The ensuing interglacial state that we live in now has prevailed for the last 11,000 years.
Analysis indicates that all of the global-scale state shifts mentioned above coincided with global scale forcing that modified atmosphere, oceans, and climate and did not resulted from cumulative effect of many smaller-scale events that originate in local systems. Global-scale forcing mechanisms today are human population growth, habitat transformation and destruction, energy production and consumption, and concurrent climate change directly induced or significantly accelerated by human activities. All of these effects far exceed, in both rate and magnitude, the forcings evident at the most recent global-scale state shift, the last glacial-interglacial transition. Human population growth and per-capita consumption rate underlie all of the other present drivers of global change. The growth in the human population now (approx. 77,000,000 people per year) is 3 orders of magnitude higher than the average yearly growth from 10,000-10,400 years ago (approx. 67,000 people per year), and the human population is nearly quadrupled in the past century. If human fertility remains at 2005-2010 levels, the population will reach 27,000,000,000 by 2100. This population size is not thought to be supportable. As a direct result of human activities, approx. 43% of Earth’s land is now converted to agricultural or urban landscapes, with much of the remaining natural landscapes networked with roads. This exceeds the physical transformation that occurred at the last global-scale state shift, when approx. 30% of Earth’s surface went from being covered by glacial ice to being ice-free. The indirect global-scale forcings that have emerged from human activities include drastic modification of how energy flows through the global ecosystem. Humans commandeer approx. 20-40% of global net primary productivity (NPP) and decrease NPP through habitat degradation. Through the release of energy formerly stored in fossil fuels, humans have increased the energy ultimately available to power the global ecosystem. The vast majority of this “extra” energy is used to support humans and their domestic animals.
By-products of altering the global energy budget are major modifications to the atmosphere and oceans. The magnitudes and direction of both local-scale direct forcings and emergent global-scale forcings are not going to change any time soon. Therefore, the plausibility of a planetary state shift seems high. Some general consequences of such event can be gleaned from the results of past global-scale shifts. Biotic effects observed in the shift from last glacial to the present interglacial periods are most relevant to biological forecasting today. There were many extinctions; drastic changes in species distributions, abundances and diversity; and the emergence of new communities. New patterns of gene flow triggered new evolutionary trajectories, but the time since then has not been long enough for evolution to compensate for extinctions. However, even on evolutionary level human influences are felt by the Earth’s biosphere: super crops’ monocultures cover previously forested areas; thousands of breeds of domestic animals were created; pests and pathogens are being distributed globally; invasive species and feral domesticates interbreed and compete with native flora and fauna. Although ultimate effects of changing biodiversity and species compositions are still unknown, if critical thresholds of diminishing returns in ecosystem services were reached over large areas and at the same time global demands increased (as will happen when the population reaches ~11,500,000,000 by approx. 2060, widespread social unrest, economic instability and loss of human life will follow. Figure 2 exemplifies the concept of Climate Shift.
Figure 2: Climate Shift
Source: National Academy of Sciences.
Ecosystems, Climate Change and Human Ecology
Climate change is a change in the statistical distribution of weather patterns when that change lasts for an extended period of time (i.e., decades to millions of years). Climate change may refer to a change in average weather conditions, or in the time variation of weather around longer-term average conditions (i.e., more or fewer extreme weather events). Climate change can also be defined as change in the statistical properties (principally its mean and spread of the climate system when considered over long periods, regardless of cause. Within scientific journals, global warming refers to surface temperature increases while climate change includes global warming and everything else that increasing greenhouse gas levels affect. Global warming is a gradual process that threatens to have serious consequences over time, including elevated sea levels, crop failure and famine, changes in global rainfall patterns, changes to plant and animal populations, and serious implications for all aspects of human life especially health and Climate change is caused by factors such as biotic and chemical processes, variations in solar radiation received by Earth, plate tectonics, and volcanic eruptions. Certain human activities have been identified as primary causes of ongoing climate change. Accordingly, fluctuations over periods shorter than a few decades, such as El Niño, do not represent climate change.
An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. These biotic and abiotic components are regarded as linked together through nutrient cycles and energy flows. As ecosystems are defined by the network of interactions among organisms, and between organisms and their environment, they can be of any size but usually encompass specific, limited spaces although some scientists say that the entire planet is an ecosystem. Energy, water, nitrogen and soil minerals are other essential abiotic components of an ecosystem. The energy that flows through ecosystems is obtained primarily from the sun. It generally enters the system through photosynthesis, a process that also captures carbon dioxide from the atmosphere. By feeding on plants and on one another, animals play an important role in the movement of matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes. Recent estimates show that climate change already causes at least 300,000 deaths per year worldwide. Three categories of risk can be differentiated:
- Direct impacts
Health and safety consequences of heat waves, floods, extreme weather events, increased concentrations of air pollutants.
- Risks through changes in ecological and biophysical systems
Changes in food yields leading to malnutrition (child stunting and death); altered flows, cleansing, and salinity levels of freshwater; changes in range, rates, and seasonality of climate-sensitive infectious diseases (climatic influences on pathogens, vector species, and intermediate-hosts animals).
- Social and economic disruptions and hardships
Diverse health disorders in climate-displaced groups; depression and despair in failing farm communities and disadvantaged indigenous and other marginalized groups. Health consequences of tension and hostilities due to climate-related declines in water, food, timber, and living space.
Bioaccumulations and Biomagnifications in Ecosystem Food Chains
Bioaccumulation is the process by which certain toxic chemical substances such as pesticides, heavy metals and polychlorinated biphenyls accumulate and keep on accumulating in living organisms, posing a threat to health, life, and to the environment. Also called bio-concentration, bioaccumulation occurs when an organism absorbs these substances at a rate faster than that at which the substances are lost by catabolism and excretion.
Biomagnification is the increase in concentration of a pollutant from one link in a food chain to another. It refers to the tendency of pollutants to concentrate as they move from one trophic level to the next. For example in the process of biomagnification, a fish at a lower trophic level accumulate mercury more rapidly than they excrete it, and every organism up the aquatic food chain contains more mercury than the one it just fed.
In the case of mercury, through bioaccumulation mercury reaches higher concentrations in biota than are present in the environmental media in the first place. Under climate change, the structure and dynamics of marine food webs are in change. Arctic marine ecosystems are further affected by the reduction of sea- ice coverage and thickness. The ability to adapt to ecosystem shifts depends on the individual species, so the effect on mercury bioaccumulation depends on the food-webs structures and their responses to climate change. Trophic structures vary geographically and occur in two ways; either from the “bottom-up”, or from the “top-down”. “Bottom-up” changes links to primary or secondary productivity, such as plankton and other organisms, stratification, nutrient supply, light intensity or ice cover. These can have major effects on the production of organisms on a higher trophic level, but the complexity of such systems does not bring any confidence in future predictions under climate change. Changes in the top of the food- web, relate e.g., to the loss of sea ice cover and subsequent a shift in diet, habitats and/or migration pathways.
Changed biotope conditions and thus changed availability of current marine fish and mammals used for human consumption, as well as increased exploitation of natural resources, may have an influence on human exposure to mercury. Climate change may affect fish supply and the associations between habitual diet and blood concentrations for many contaminants. Furthermore, it is a serious concern that climate change will cause changes that affect the supply of traditional foods such as marine mammals and reindeer for people living in the Arctic. It has been concluded that the traditional foods and local products are more nutritionally adequate than the imported foods replacing them. Severely limiting the consumption of fish and seafood may do more harm than good by reducing the consumption of foods with health benefits and by increasing the consumption of alternative foods that have potential health risks such as increasing the possibility of obesity and diabetes.
Causes of Bioaccumulations and Biomagnifications
The release of toxic chemicals and pollutants into the environments such as the seas, air, and land results in the accumulation of toxins and harmful substances in the environment. The concentration of these toxic chemicals and pollutants seem to be very low when released in different environments, it eventually accumulates and gets absorbed by lower organisms in the food chains such as fish, earthworms, and plants. When the lower organisms are eaten by other organisms and the process goes up the trophic levels, biomagnifications occurs.
- Agricultural activities: According to the EPA, agricultural soil management practices can lead to production and emission of nitrous oxide (N2O), a major greenhouse gas and air pollutant. Activities that can contribute to N2O emissions include fertilizer usage, irrigation and tillage. The management of soils accounts for over half of the emissions from the Agriculture sector. Cattle livestock account for one third of emissions, through methane emissions. Manure management and rice cultivation also produce gaseous emissions. Agricultural pesticides, fungicides, herbicides, and chemical fertilizers, among other agricultural chemicals are highly toxic and often find way into the soils, rivers or lakes and the seas through surface storm water runoff. The primary agricultural inputs including pesticides, industrial by-product wastes, some fertilizers, and specific agrochemical products contain traces of heavy metals such as arsenic, cadmium, mercury, copper and lead. These substances cause severe health impacts to humans and aquatic animals such as fish when indirectly ingested and accumulate in the body tissues. Farming can deplete soil carbon and render soil incapable of supporting life; however, the study also showed that conservation farming can protect carbon in soils, and repair damage over time. The farming practice of cover crops has been recognized as climate-smart agriculture.
2. Organic contaminants: Manures and Biosolids frequently contain nutrients including nitrogen, carbon, phosphorus and nitrogen. Furthermore, because they are industrially processed, they may also have within them contaminants such as personal care products (PPCPs) and pharmaceuticals. These products have been found in human and animal bodies and are believed to have negatively health impacts to wildlife, animals, and humans.
- Industrial manufacturing activities and pollution: The manufacturing processes of industries indirectly or directly release toxic and harmful substances that find a way to the soils, rivers, lakes and oceans. Industrial processes pollute the environment in several ways by emitting or discharging toxic pollutants into the environment that find way into the food chain, leading to biomagnifications
- Mining activities in the ocean: Mining activities in the deep sea is to extract minerals and metal ores like zinc, cobalt, silver, aluminum and gold destroy the oceans and the coastal regions as the mining processes generate scores of sulfide and selenium deposits in the waters. The toxicity levels build up and are absorbed by ocean creatures that are then consumed by organisms in the higher trophic levels of the food chain.
Anticipated Changes in the Source–Pathway–Receptor Relationship
For humans to be affected directly, chemicals must move through a pathway often called the source-to-receptor pathway. After being released from some source and moving through the environment, often being transformed by physical or biological factors in the process, chemicals must come into contact with and enter the body of a human. Once in the body, chemicals are subject to human toxicokinetic processes, ultimately coming in contact with some target tissue or molecular receptor to initiate an adverse outcome (Fig. 3). This chain of events is often complex, involving transformation of chemicals in the environment and their uptake and accumulation in organisms that play a role in exposing humans to those chemicals (e.g., consumption of contaminated fish). Changes in climate and associated changes in weather patterns, as well as non-climate-related drivers, are anticipated to affect various points in the source-to-receptor pathway, modifying how and to what extent humans are exposed to toxic chemicals and how they respond to harmful effects from those exposures.
Adaptation to GCC can influence the use and release of chemicals into the environment. For example, the types of pesticides, pharmaceuticals, and veterinary medicines used and the timing and frequency of their use will likely differ from today in response to changing disease and pest pressures resulting from GCC. Biocide use, for example, is likely to increase in response to increases in animal and plant pests and diseases that may arise from increasing temperature and humidity. Expected decreases in fossil fuel use resulting from greenhouse gas mitigation policies will likely reduce ground-level air pollution by particulate matter and ozone in urban areas, while shifts in the production of some types of biofuels may increase levels of air pollution in rural areas; also, their use may increase their combustion product exposures. In addition to changing human patterns of chemical use and other behaviors, GCC may affect the rates of formation of natural toxins (such as fungal and algal toxins) in the environment as well as the geographical distribution of these substances.
It is also likely that GCC will combine with other natural and anthropogenic factors to affect the transport and transformation of toxic chemicals in the natural environment. Increases in temperature can result in increased volatilization of persistent organic chemicals (e.g., at contamination sources such as buildings and electrical equipment), thereby increasing amounts subject to long-range transport. Increases in temperature and changes in moisture content are likely to alter the persistence of chemicals. Alterations in soil characteristics (organic carbon, dustiness) and hydrology may change how contaminants are transported around a terrestrial ecosystem as well as the dilution potential of contaminants in rivers and streams. Increases in the occurrence of extreme weather events, such as floods and droughts, will likely alter the mobility of contaminants. For example, flood events have been shown to transport dioxins, metals, and hydrocarbons from contaminated areas to noncontaminated areas. In agricultural areas, changes in irrigation practices in response to GCC could also move contaminants from water bodies onto land. Changes in the degree and duration of ice cover may affect the degradation of contaminants in some regions. For legacy contaminants, such as mercury, that have been released to the environment in the past and reside in soil and sediments, GCC may alter the environment in such a way that the substances are remobilized or released more rapidly.
Effects of GCC on human exposure to chemicals
Changes in the sources, fate, and transport of chemicals will have both positive and negative implications for contamination of food, drinking water supplies, air, and, hence, human exposure However, very few studies have been performed to quantify the likely changes in exposure concentrations. There are quantified effects of changes in the use, fate, and transport of pesticides, resulting either directly or indirectly from GCC, on surface water and groundwater concentrations. It has been proved that concentrations of pesticides in surface waters and ground waters are likely to increase under GCC and that, for some pesticides, peak concentrations could increase by orders of magnitude. The indirect effects of GCC (i.e., effects on amount of pesticide applied and application timing) on surface-water exposure were found to be stronger than the impact of changes in the climate alone on chemical fate and transport. Additional studies of this type are needed for other classes of pollutant and other geographical regions.
Global climate change will affect not only the concentrations of toxic chemicals in water, food, and air, but also how humans interact with these media; this will also have implications for the degree of human exposure. For example, reduction in the availability of drinking water for many populations could change exposure to waterborne contaminants as human populations shift toward other sources of drinking water (e.g., water from water-reuse and reclamation systems) Changes in climate may also impact the amounts of time humans spend indoors and outdoors, influencing exposure to both indoor and outdoor contaminants. Figure 3 shows the Source–pathway–receptor relationship, showing interactions with both climate and non-climate stressors.
Figure3: Source–pathway–receptor relationship, showing interactions with both climate and non-climate stressors. GCC=global climate change.
There is concern about these phenomena of bioaccumulation and biomagnifications because together they mean that even small concentrations of chemicals in the environment can find their way into organisms in high enough dosages to cause problems. Biomagnification, also known as bioamplification or biological magnification, is the increasing concentration of a substance, such as a toxic chemical, in the tissues of organisms at successively higher levels in a food chain. Human beings are at higher levels of most food chains In order for biomagnifications to occur, the pollutant must be long-lived, mobile, soluble in fats and biologically active .If a pollutant is short-lived, it will be broken down before it can become dangerous. If it is not mobile, it will stay in one place and is unlikely to be taken up by other organisms. If the pollutant is soluble in water, the organism will excrete it. Pollutants that dissolve in fats, however, may be retained for a long time. If a pollutant is not active biologically, it may biomagnify, but we really do not worry about it much, since it probably will not cause any problems. Pollutants of importance are plastics, radioisotopes (which may be both toxic and radioactive!) and oil.
Plastics are eaten by many organisms and can cause mechanical injury, strangulation, or starvation. Radioisotopes can damage biological molecules, particularly DNA, leading to cancer, other illnesses, or death. Oil smothers aquatic organisms, cutting them off from oxygen. It can also infiltrate the insulating feathers of seabirds (or fur of sea-going mammals) and cause them to die from hypothermia (or cause them to sink). Oil spills are a serious problem in marine environments.
Biological magnification often refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the food chains. Bioaccumulants are substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted. The contaminants include heavy metals namely mercury, arsenic, pesticides such as DDT, and polychlorinated biphenyls (PCBs) compounds which are then taken up by organisms because of the food they consume or the intoxication of their environment.
Biomagnification stands for Biological Magnification, which means the increase of contaminated substances or toxic chemicals that take place in the food chains. These substances often arise from intoxicated or contaminated environments. These materials are present in a variety of household and industrial chemicals. The harmful substances then build up inside the organism’s cells. When organisms higher in the food chain consume the organisms containing the toxins below their trophic levels, the toxins gradually become concentrated in the higher food chain. Because this is a repetitive process in the ecosystem and throughout the entire food chain, the higher organisms are the ones that will accumulate most of the toxins. Higher organisms in most food chains include human beings.
There are two main groups of substances that biomagnify. Both are lipophilic and not easily degraded. Novel organic substances are not easily degraded because organisms lack previous exposure and have thus not evolved specific detoxification and excretion mechanisms, as there has been no selection pressure from them. These substances are consequently known as “persistent organic pollutants” or POPs. The other group is metals. Metals are not degradable because they are elements. Organisms, particularly those subject to naturally high levels of exposure to metals, have mechanisms to sequester and excrete metals. Problems arise when organisms are exposed to higher concentrations than usual, which they cannot excrete rapidly enough to prevent damage. Some persistent heavy metals are especially dangerous and harmful to the organism’s reproductive system.
The following are some effects of bioaccumulations and biomagnifications on human ecology
1. Impact on human health
Humans become more susceptible to cancers, liver and kidney failure, respiratory disorders, birth defects in pregnant women, brain damage, and heart diseases are a result of mercury, cadmium, lead, cobalt, chromium and other chemical poisoning. For instance, diseases like hepatitis and cancer have been attributed to consuming seafood that has been poisoned by mercury and polycyclic aromatic hydrocarbons (PAHs).
2. Effects on reproduction and development of marine creatures
The various toxic chemicals and elements accumulate in the vital organs of the various aquatic creatures affecting their reproduction and development. For instance, seabird eggs are laid with thinner shells than normal, and can result in the birds crushing their eggs instead of incubating them. Selenium and heavy metals such as mercury also affect the reproduction of aquatic creatures such as fish as it destroys their reproductive organs. Besides, PCB’S (polychlorinated biphenyls) also biomagnifies and impairs reproduction and is considerable high in aquatic systems.
3. Destruction of the coral reefs
The coral reefs are destroyed by cyanide that is used in leaching gold and in fishing. The reefs provide for spawning, feeding, and dwelling grounds for numerous sea creatures. When destroyed, the survival of aquatic creatures is highly compromised.
4. Disruption of the food chains
Many sea creatures depend on the natural food chains for survival. When chemicals and other toxins are carried into the soils, rivers, lakes or oceans and taken up by various organisms, which disrupt the interconnected relationships within the food chains and food webs. It happens when small animals ingest or plants absorb the toxic elements after which large animals at higher trophic levels consequently eat them affecting the entire natural food chains. The creatures or plant in the food chains intoxicated with substances such as mercury, copper, chromium, cobalt, lead, selenium, among others. This leads to susceptibility to diseases, reproductive disorders, and even deaths. Humans are not exempted in this.
Conclusions and Recommendations
Impacts from climate change are happening now across the globe. Ecosystems and human communities are currently being affected. These impacts extend well beyond just an increase in temperature across the globe. Multiple sectors of our society, spanning across regional boundaries are being affected. Already impacted are are: water, energy, transportation, wildlife, agriculture, ecosystems, and human health.
The main current international agreement on combating climate change is the Kyoto Protocol, which came into force on 16 February 2005. The Kyoto Protocol is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC). Countries that have ratified this protocol have committed to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases.
Human health is vulnerable to climate change. The changing environment is expected to cause more heat stress, an increase in waterborne diseases, poor air quality, extreme weather events, and diseases transmitted by insects and rodents. Ecosystems are also being affected by the changes that are occurring: habitats are being modified, the timing of events such as flowering and egg laying are shifting, and species are changing their home ranges. Changes are also occurring to the ocean. The ocean is absorbing about 30% of the carbon dioxide that is being released into the atmosphere from the burning of fossil fuels. As a result the ocean is becoming more acidic. Marine life is being affected by this ocean acidification. Along the coasts, higher sea levels cause these areas to be at a greater risk of erosion and storm surges.
Across the world, changes to water resources are of critical concern. In some regions, drought is an important factor and conditions are critically affecting local communities. In many regions, floods and water quality problems are likely to be worse because of climate change. Climate change has increased water stress. Few things are more important to human quality of life than easy access to clean water. Our food supply is dependent on climate and weather conditions. Although agricultural practices may be adaptable, changes like increased temperatures, water stress, diseases, and weather extremes create significant challenges for the farmers and ranchers who put the food on our tables.
Global climate change may affect multiple steps in the process of human exposure and harm to human health from chemical risks, including emissions from sources, transport and transformation in the environment, and human behaviors and vulnerabilities. For many chemical contaminants, a net increase in exposure is likely in certain regions of the world. While GCC will affect the fate and transport of chemicals in multiple and complex ways, in many cases the main climate-related drivers influencing human exposure will be changes in the types of chemicals used by society, alterations in the amounts and patterns of chemical use, and changes in the rates of formation of natural toxins in natural systems. Also, GCC will affect the way in which human populations interact with the natural environment so as to alter the degree of exposure. Alongside changes in exposure, changes in the sensitivity of humans to chemical exposure are expected due to factors such as increases in the levels of heat stress, psychosocial factors, suppression of the immune system, and alterations in nutritional status due to changes in diet and the quality of foodstuffs.
While each individual impact of GCC on chemical exposure and human sensitivity may not be highly significant and may occur in either a positive or a negative direction, the potential cumulative impacts of multiple influences could significantly alter risks to human health. Despite significant uncertainties, the preponderance of the current evidence suggests that many human health risks from chemicals may be increased in the future if a business-as-usual approach is adopted. Changes in risks are likely to be most significant for chemicals where microbes, plants, and lower animals are involved in the source-to-receptor pathway. Increases in risks are likely to be seen for the natural toxins that are produced by microbes, algae, and plants. The risks of chemicals, such as pesticides, whose use is determined by population responses of fungi, weeds, and lower-order animals, or those, like mercury, whose speciation is altered by the activity of micro-organisms, will also be significantly affected. While the absolute magnitude of changes in average air concentrations related to GCC may be relatively small for a given air pollutant, widespread human exposures, increased peak concentrations in certain geographical areas, and significant health consequences make such impacts of GCC very important from a public-health standpoint.
These alterations in risks have implications for national and international decision makers involved in the regulation and authorization of chemical products and the monitoring and management of chemicals in environmental matrices and foodstuffs. The expected changes reveal that some of the scenarios and models currently used in health risk assessment of chemicals will need updates and revision in order to reflect some of the future changes described earlier. Monitoring methodologies may also need to be adapted in order to cope with increased variability in exposure, sensitivity, and risk, both spatially and temporally. Monitoring and sampling should be done at a frequency sufficient to capture variability, which is likely to increase in many places.
It is also important to recognize that human exposure to chemicals in the environment in the future will be affected by other, non-climate-related drivers such as increased urbanization, future technological developments (such as a move toward more environmentally benign pesticides), ongoing strategies to reduce emissions and other environmental releases (e.g., of persistent organic pollutants), and economic changes. In some cases, these drivers may have a bigger impact on human exposure (either increasing or lowering exposures) and risks than GCC alone.
There are, however, major gaps in our current understanding of how chemical risks will change. A concerted effort is therefore needed at an international level to better characterize the potential impacts of GCC and other future drivers on exposure, sensitivity, and risk. We recommend that work should focus on the following areas. First, the development of future models and scenarios of land use and social, technological, and economic change in order to provide a basis for informing how inputs of chemicals to the environment, in different regions of the world, may change in the future. Second, work should focus on the generation of improved data sets and models for determining future human exposure to chemicals in different environmental matrices. This work should consider the importance of emerging exposure pathways, such as increased inhalation of contaminated dust or exposure consequences of flooding, and consider the implications of human behavioral change on the degree of exposure. Furthermore, there should be focus the development of research programs that aim to fill gaps in our understanding of the interactions between climate and weather parameters and human sensitivity to chemical exposures. Focus should also be given to the refinement of regulatory models and procedures in the light of knowledge gained from work on exposure and human sensitivity to toxicants. Existing risk assessments and chemical management programs should also be updated to determine whether the risks of a current-use product could change in the future. Finally, work should give focus to the development of targeted surveillance schemes for the presence and health effects of select chemicals in different environmental compartments for different regions of the world and at smaller geographical scales to address inequities at the community level.
To address these knowledge gaps, input is required from a wide range of disciplines (including climate science, toxicology, exposure science, public health, environmental modeling, social science, economics, and environmental chemistry) and a range of sectors across the globe. It is essential that future research and assessment programs take a holistic approach and do not just focus on GCC-driven changes alone. Research programs should also include elements of technology transfer and capacity building for developing countries struggling to adapt to GCC impacts, many of which will be most vulnerable to the forecast changes in chemical exposure. Figure 4 below shows the conclusive working model envisaged in this review paper.
- Figure 4: The Relationships between Global Climate Change, Bioaccumulations, Biomagnifications and Human Ecology
Source: Nyongesa K.W, 2017
GCC Alterations in Chemical fate and Transport
Increased temperatures can increase metabolic rates for many organisms, thereby increasing the potential for bioaccumulation and biomagnification of some contaminants. Temperature-related increases in the uptake and bioaccumulation of metals have been reported for several marine organisms, including crustaceans, echinoderms, and mollusks. In a recent modeling exercise of the uptake of methylmercury, increases in temperature resulted in increased concentrations of the compound in fish and mammals; temperature increases would also be expected to accelerate the conversion of mercury to methylmercury. In some instances, uptake may decrease. Studies of organochlorine concentrations in fish between 1994 and 2008 showed a decline in concentrations with increasing temperature, a trend that could be explained by declines in lipid content over time. The reason for the change in lipid content and a possible association with climate effects are unclear.
I shall be remiss without appreciating the work of Prof. Shem Wandiga, Prof. Dan Olago and Prof. Nicholas Oguge of the Institute of Climate Change and Adaptation (ICCA), University of Nairobi for mentoring, teaching and supervising my Doctoral Research. My research work was entitled Vulnerability Assessment of Terrestrial Large Mammals as Indicators Species to Climate Change in Mt. Elgon National Park, Kenya. The Professors demonstrated profound knowledge and understanding of the concepts and complexities encapsulate in the study of Global climate change.
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Nyongesa K. W. (2017)A paper for presented at the “Symposium on Climate Change and Droughts Resilience in Africa”, Nairobi, Kenya, 16th-18th October 2017] at Strathmore University
Nyongesa K. W.,Omuya B.S., Sitati N.W. Impacts of Climate Change on Ecosystems and Biodiversity and Implications on Sustainable Development. The Cradle of Knowledge: African Journal of Educational and Social Science. Volume 4: No.1, 2016. ISSN2304-2885.
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Kennedy W. *Nyongesa1 Matonyei Lelei and Francis O. Obiria
1,2 Kitale National Polytechnic, Department of Mathematics and Applied Sciences.
Kisii University- Francis O. Obiria
Corresponding email: email@example.com
The Monoclimax theory proposes that the generation of a climax community is solely the control of the climate of the region. Therefore, the climax community becomes the “index” of that region. In most temperate forests in United States of America.; climate change led to substantial increase in some species and decline in some. In tropical Africa, prediction of biotic responses to future climate change trends is based on two modelling approaches: bioclimatic species envelope models and dynamic vegetation models. Another complementary but underused approach is to examine biotic responses to similar climatic changes in the past as evidenced in fossil and historical records. This paper discusses climate change as one of the drivers of ecological succession and how it determines the type of climax community obtained. A Climax community is the final community in the process of ecological succession. Ecological succession is a fundamental concept in ecology. It refers to changes in the composition or structure of an ecological community; a series of progressive changes over time. Succession may be initiated either by formation of new, unoccupied habitat such as a lava flow, a severe landslide or by some form of disturbance such as fire or logging. The former case is referred to as primary succession, the latter as secondary succession. In primarysuccession, newly exposed or newly formed rock is colonized for the first time. In secondarysuccession, an area previously occupied by organisms is disturbed then re-colonized following the disturbance. The trajectory of ecological change can be influenced by site conditions, by the interactions of the species present, and by stochastic factors such as availability of colonists, seeds or climatic and weather conditions. Some of these factors contribute to predictability of succession dynamics; others add probabilistic elements. Communities in early succession will be dominated by fast-growing, well-dispersed or r-select species. As succession proceeds, these will be replaced by more competitive k-selected species. This review paper brings in view a concept map that relates the different concepts and sub-concepts in ecological succession.
Key Words: Climate Change, Ecological Succession, Climax Communities, Concept Map, Garden Plot
Ecologists have a strong interest in understanding how communities form and change over time; this stage of climax community has been the object of much scrutiny and attention from ecologists, because it is rare and so many different possibilities can theoretically arise, depending on the path of succession. However, studies have shown that every climax community has a certain specific set of characteristics: 1) They have high tolerance to ecological disturbances. 2) They have a “middle path”, i.e. they have moderate conditions, also called mesic conditions. 3) They have high species diversity, and transfer of energy is in the form of complex food webs, not simple food chains.4) The size of organisms in the community is large, and they all have their specific niches. 5) Net community production is low, while biomass and organic matter is high. 6) Mineral cycles and nutrient exchange in the community is slow. But this is where the unanimous agreement of ecologists ends. How does the climax community originate and what controls their composition? This has been a matter of great debate for much of the 20th and 21st centuries. Three theories have taken the forefront, and the ecological community is split between them.
a) Monoclimax theory
Clements (1916) advanced this theory when he studied communities in the early part of the 20th century. This theory states that the generation of a climax community is solely the control of the climate of the region. Therefore, the climax community becomes the “index” of that region. He argued that within the same type of climate, the adaptations and requirements of organisms remain the same. It is also possible that two communities will have formed with the presence of the same pioneer species. Hence, the way they modify their surroundings (which eventually leads to change in communities) will also be largely the same. Consequently, each climactic region is characterized by climax communities where a few specific species are dominant in the climax community.
The Monoclimax theory, as developed by Clements (1916, 1936), is often described as the origin of dynamic ecology. According to this theory there is only one climax community in a climatic or geographical region. But topographic differences and different soil types form other communities in the same zone. These communities are known as subordinate communities. The subordinate communities may be proclimax, post climax, disclimax, preclimax, and subclimax communities: (a) Proclimax: The community which is more or less stable resembling the climax community is called proclimax (b)Disclimax: The community disturbed by man or other animals is called disclimax community. Its example is grassland in forest area (c) Subclimax or preclimax: The community in which development is stopped in the subtinal matte of succession due to burning, cutting or grazing and flooding is called subclimax or preclimax community (d) Postclimax: The community in which a strip of vegetation of higher life form is found within a climax is called post climax community. Its example is forest strip along a stream in grassland.
Daubenmire (1968) criticized this theory, proposing that climate is the sole control of climax communities. According to Daubenmire, believing in the Monoclimax theory meant admitting that all factors other than climate are secondary in nature. What is the alternative? It is the possibility that all environmental factors are equally important, and accordingly, many climax communities can exist.
b) Polyclimax theory
Tansley proposed this in 1939. This theory suggests just that according to a controlling influence by each environmental factor, which becomes dominant purely as a matter of chance, there can be several climax communities. According to this, there is a particular climax community for a region called climactic-climax community (Tansley, 1920., 1929., 1939). However, other factors can prevent the community from reaching this stage. For example, consider a community that has been affected by a road construction project. This area has an overriding influence enforced by humans; therefore, it cannot reach its climactic-climax. One of the earlier seral stages may be stabilized in such a situation and forms a “pre-climax” or a “sere-climax”.
It is also possible that an entirely new community can be established, that is vastly different from the expected climactic-climax. Since the overriding influence was of humans, the climax is known as anthropogenic climax. Different climaxes, based on different factors having an overriding influence have been proposed. During succession the floristic convergence is only partial. There may be more than one type of stable endpoint. These alternative stable endpoints are controlled by local factors such as topographic position or soil type, consequently, called topographic climax, edaphic climax, fire climax among others as opposed to “climatic climax”. In contrast, Clements regarded these as “sub climaxes.” Tansley’s Polyclimax theory is: (a) an equilibrium model (b) less deterministic than Monoclimax theory. According to this theory a number of different climax communities are present in climatic or geographical region. Thus proclimax, disclimax, preclimax, and postclimax communities are all climax communities. They are all self-reproducing communities. They can maintain themselves or an indefinite period of time. This theory does not rule out climax communities. But it gives other stages of communities as full status of climax communities. Thus these are not regarded as in minor communities
c) Climax-Pattern Hypothesis
Whittaker (1951) proposed this concept that was entirely new. According to him, the climax community was controlled by all environmental factors equally. Therefore, no one climax is established in isolation. A series of climax communities are established, parallel to each other depending on the changing environmental gradients. According to this theory the structure, composition and other characters of the climax communities are determined by the total environment of the ecosystem. It is not determined by a single factor. A Climax community is composed of a number communities.
To that end, the authors in this review paper agree with the Polyclimax theory as far as saying that many different factors can influence the occurrence of the climax community and its composition. There will also be some factors more dominant than others in a given area. However, it is also important to understand that communities never occur in isolation. There is always a gradual change from one community to another. Therefore, in a given region with changing communities, the environmental factors will also change accordingly. This will alsohave an impact on the resulting community composition. Different community structures based on different environmental parameters can occur parallel to each other as these conditions gradually change from one to another.
For example, a community of trees at a particular elevation will gradually change into another community composition as the elevation changes. Along with this change in elevation, temperature and soil conditions will also change. Different permutations and combinations arise with just these three factors (3×3=9), resulting in the possibility that any number of climax communities out of the possible 9 can occur in that area simultaneously.
Foundational Studies on Ecological Succession and Climax Communities
Early sources of the concept of climax include and the American work of Cowles (1899, 1901) and Clements (1916). Ecologists seek to capture with concepts the meaning of vegetation change Whittaker (1974). The idea that this change could be described and understood was a major development in the history of ecology, that may be traced back to Kerner (1863 in Whittaker,1974), Hult (1885, 1887 in Whittaker,1974), Warming (1891, 1896 in Whittaker,1974), Lüdi (1921, 1930 in Whittaker,1974), Cain (1939) and Whittaker (1951). In counterbalance to the idea of vegetation change it was natural to recognize the condition of relative vegetational stability that came to be known as “climax”.
Ecological Succession in Context
When the planet first formed, there was no soil. Hot magma and cold water make hard rocks, as seen by newly formed islands. Primary ecological succession is the process of small organisms and erosion breaking down these rocks into soil. Soil is then the foundation for higher forms of plant life (He, 2008); these higher forms can produce food for animals, which can then populate the area as well. Eventually, a barren landscape of rocks will progress through primary ecological succession to become a climax community.
Morin and Thuiller (2009) assert that, after years and years, the soil layer increases in thickness and harbors many nutrients and beneficial bacteria that are required to support advanced plant life. Further, if this primary ecosystem is disturbed and wiped out, secondary succession can take place, and small plants will come back first. After they create a solid layer of vegetation, larger plants will be able to take root and become established. At first, small shrubs and trees will dominate. As the trees grow, they will begin to block the light from most of the ground, which will change the structure of the species below the canopy. Eventually, the ecosystem will arrive at a climax community, which may or may not be the similar to the original community. It all depends on which species colonize the area, and which seeds are able to germinate and thrive.
Cyclic ecological succession happens within established communities and is merely a changing of the structure of the ecosystem on a cyclical basis (Deluca et al., 2009); some plants thrive at certain times of the year, and lay dormant the rest. Other organism, like cicadas, lay dormant for many years and emerge all at once, drastically changing the ecosystem.
Bryant et al. (1998) posit that, while ecological succession is a term coined by botanists, it also applies heavily to animal a population that goes through a disruption. For instance, a coral reef; the coral reef as an ecosystem did not just happen into existence, but like many plant communities had to be formed over time through ecological succession. The primary ecological succession in a coral reef is the colonizing of rocks by small coral polyps. These polyps will grow and divide many times to create coral colonies. The shapes and shelter of the coral colonies eventually attract small fish and crustaceans that live in an around the coral. Smaller fish are food for larger fish, and eventually a fully functioning coral reef exists. The principles of ecological succession, while developed in context to plants, exist in all established ecosystems.
Temperate deciduous forests are among the major biomes on earth and provide important ecological, economic, and social services to society (FAO 2012); most temperate deciduous forests in the eastern U.S. experienced heavy exploitation in the 19th and early 20th centuries and some of these were completely deforested while others are now recovering. These recovering forests are in intermediate stages of development and are undergoing rapid succession changes as a result of growth, competition, dispersal, and establishment (Shifley et al., 2012). Most temperate forests in U.S. are recovering from heavy exploitation and are in intermediate succession stages where partial tree harvest is the primary disturbance. Changes in regional forest composition in response to climate change are often predicted for plant functional types using biophysical process models. These models usually simplify the simulation of succession and harvest and may not consider important species-specific demographic processes driving forests changes.
According to Schumacher and Bugmann (2006), by use of the forest landscape modeling approach to project changes in density and basal area of 23 tree species due to succession, harvest, and four climate scenarios from 2000 to 2300; on average, succession, harvest, and climate change explained 78%, 17%, and 1% of the variation in species importance values at 2050, respectively, but their contribution changed to 46%, 26%, and 20% by 2300.
Climate change led to substantial increases in the importance of red maple and southern species e.g. yellow-poplar and decreases in northern species e.g. sugar maple and most of widely distributed species e.g. the white oak (Schuler, 2004); harvest interacted with climate change and accelerated changes in some species like the increase in southern red oak and decrease in American beech, while ameliorated the changes for others such as increasing red maple and decreasing white ash. Succession was the primary driver of forest composition change over the next 300 years by this model. The effects of harvest on composition were more important than climate change in the short term but climate change became more important than harvest in the long term (Brandt et al., 2014).
According to Iverson et al. (2008), the results show that it is important to model species-specific responses when predicting changes in forest composition and structure in response to succession, harvest, and climate change. As large-scale industry timber harvest moved from temperate deciduous forests to other less explored forest biomes, fine spatial scale (<10 ha) non-industrial timber harvest, mostly in the form of partial harvest of large trees of preferred species, becomes the primary anthropogenic disturbance (Shifley et al., 2012). These disturbances can change forest composition and structure and alter succession trajectories (Deluca et al., 2009). Furthermore, climate change may affect species establishment and mortality and alter forest composition in the region (Morin and Thuiller, 2009).
Predictions of forest change at regional scales (>100 million ha) often rely on niche and biophysical process models (Morin and Thuiller, 2009). Niche models (also called bioclimatic envelope models) relate observed species’ distributions to environmental predictors using a variety of statistical methods and have been extensively used to predict the potential impacts of climate change on tree species distributions (Guisan and Thuiller, 2005, Boulangeat et al., 2012). Recent advances in niche models include dispersal functions to predict species range shifts accounting for the effects of seed source, habitat fragmentation, and dispersal distance (Iverson et al., 2008, Meier et al., 2012). Biophysical process models, on the other hand, predict stock (e.g., biomass) and fluxes (e.g., aboveground net primary production) of plant functional types by incorporating leaf photosynthesis, carbohydrate allocation, and nutrient and water cycling (Morin et al., 2008, Medvigy et al., 2009). Despite the recognized importance of succession and harvest, both niche and process models usually use coarse spatial resolutions (e.g., 10–20 km) in regional scale predictions and consequently succession and disturbances (e.g., harvest and fire) are either simplified or ignored (Neilson et al., 2005, Purves and Pacala, 2008, Iverson et al., 2011, McMahon et al., 2011). Therefore, we still lack an understanding of the relative importance of succession, disturbance, and climate change in determining future forest composition changes.
Forest landscape models are explicitly designed to incorporate site-scale succession and landscape-scale disturbance to simulate forest change at landscape scales (He and Mladenoff, 1999). They have been recently used to examine the relative importance of succession, disturbance, and climate change in affecting forest change (e.g., biomass) at landscape scales (e.g., 104–107 ha). For example, Scheller and Mladenoff (2005) used the LANDIS II forest landscape model in northern Wisconsin and found that tree harvest and wind were as important as the effects of climate change alone in influencing the magnitude of forest composition change and the direction of tree species richness change.
Schumacher and Bugmann (2006) used the LANDCLIM forest landscape model in the Swiss Alps and projected that climate change would cause extensive forest cover changes beginning in the coming decades, fire was likely as important as climate, and harvest was less important compared with the direct effects of climate change. Gustafson et al. (2010) used the LANDIS II model in south-central Siberia and found that biomass was more strongly affected by timber harvest and insect outbreaks than by the direct effects of climate.
Wang et al. (2014) posit that studies investigating the relative importance of these endogenous and exogenous processes at regional scales and spanning short- to long-time frames have rarely been done; this is mainly because forest landscape models were unable to operate at sufficiently large geographic extents with a resolution fine enough to represent site- and landscape-scale processes. Maximum simulation capacity (number of pixels) of forest landscape models was in the range of 106 ~ 107 cells (He, 2008).
Recent advances in the LANDIS PRO forest landscape model have expanded the simulation capacity to 108 cells at 90–270 m resolution (Wang et al., 2014); the simulation capacity of LANDIS PRO makes it possible to predict forest change for a large temperate deciduous forest region under alternative climate scenarios while mechanistically simulating site- and landscape-scale processes. The future forest composition and structure can be assessed based on projected density, basal area, importance values, and biomass of tree species down to the raster cell level.
Climate change is degrading current habitats and will likely create novel habitats as species with good dispersal mechanisms redistribute themselves to track a shifting climate envelope (IPCC (2007); climate change is impacting and changing the species composition of natural habitats, but the refugia where these natural habitats occur nevertheless represent our best option for long-term biodiversity conservation. Existing natural communities are defined by unique arrays of environmental characteristics and the suite of species that interact within them. Rare species are often indicators of specialized or unique habitats. Even if some species are lost from special habitats, and some migrate in or out, the unique set of environmental characteristics will remain to provide the basis for a rich palette of opportunities for species in the future. Rare species and special habitats should be a priority for conservation action. Successful adaptation strategies for fish and wildlife will require understanding and reducing the combined effects of both climate-related and non-climate stressors. The cumulative effects of habitat loss and alteration, pollution, invasive species, and pathogens in addition to climate change may prove to be a deadly combination for many species. Ecological succession is one of the major observations on any Nature Trail. It is possible to observe both the on-going process of succession and the consequences of past succession events at almost any point along the trail. The rise and the decline of numerous species within our various communities illustrate both of the types of motive forces of succession: the impact of an established species to change a site’s environmental conditions, and the impact of large external forces to suddenly alter the environmental nature of a site. Both of these forces necessarily select for new species to become ascendant and possibly dominant within the ecosystem.
Some specific examples of ecological succession observable in tropical and temperate regions include:
- The growth of hardwood trees (including ash, poplar and oak) within the red pine planting area in tropical and temperate forests. The consequence of this hardwood tree growth is the increased shading and subsequent mortality of the sun loving red pines by the shade tolerant hardwood seedlings. The shaded forest floor condition generated by the pines prohibits the growth of sun-loving pine seedlings and allows the growth of the hardwoods. The consequence of the growth of the hardwoods is the decline and senescence of the pine forest.
- The raspberry thickets growing in the sun lit forest sections beneath the gaps in the canopy generated by wind-thrown trees in temperate forests. Raspberry plants require sunlight to grow and thrive. Beneath the dense shade canopy particularly of the red pines but also beneath the dense stands of oaks, there is not sufficient sunlight for the raspberry’s survival. Whenever there is a tree fall the raspberry canes have proliferated into dense thickets. Within these raspberry thickets, are dense growths of hardwood seedlings. The raspberry plants are generating a protected “nursery” for these seedlings and are preventing any major browser of tree seedlings from eating and destroying the young trees. By providing these trees a shaded haven in which to grow the raspberry plants are setting up the future tree canopy which will extensively shade the future forest floor and consequently prevent the future growth of more raspberry plants.
- The Succession “Garden” plot. This plot was established in April, 2000. The initial plant community that was established within the boundaries of this plot was made up of those species that could tolerate the periodic mowing that “controlled” this “grass” ecosystem. Soon, though, other plant species became established as a consequence of the removal of the stress of mowing. Over time, the increased shading of the soil surface and the increased moisture retention of the undisturbed soil-litter interface allowed an even greater diversity of plants to grow and thrive in the Succession Garden. Eventually, taller, woody plants became established which shaded out the sun-loving weed community. In the coming years we expect tree seedlings to grow up within the Succession Garden and slowly establish a new section of the forest.
Concept maps are graphical tools for organizing and representing knowledge. They include concepts, usually enclosed in circles or boxes of some type or without circles or boxes; and relationships between concepts indicated by a connecting line or arrow line linking two concepts. A concept is perceived as regularity in events or objects or records of events or objects, designated by a label. The label for most concepts is a word, although sometimes symbols such as + or %, and sometimes phrases more than one word are used. Propositions are statements about some object or event in the universe, either naturally occurring or constructed. Propositions contain two or more concepts connected using linking words or phrases to form a meaningful statement. Sometimes these are called semantic units, or units of meaning.Figure1 shows the Concept Map as contemplated in this review paper; the Concept Map shows the multidimensional inter-connectedness of the different related concepts and sub-concepts in ecological succession, climax communities and climate change.
Figure 1: Multidimensional Inter-connectedness of the different related concepts and sub-concepts in ecological succession.
Sources: Nyongesa and Matonyei, 2019
Ecological succession is a force of nature. Ecosystems, because of the internal species dynamics and external forces, environmental drivers including climate change are in a constant process of change and re-structuring. To appreciate how ecological succession affects humans and also to begin to appreciate the incredible time and monetary cost of ecological succession, one only has to visualize a freshly tilled garden plot. Clearing the land for the garden and preparing the soil for planting represents a major external event that radically re-structures and disrupts a previously stabilized ecosystem. The disturbed ecosystem will immediately begin a process of ecological succession. Plant species adapted to the sunny conditions and the broken soil will rapidly invade the site and will become quickly and densely established. These invading plants are called “weeds”. “Weeds” have very important ecological roles and functions, but weeds also compete with the garden plants for nutrients, water and physical space. If left unattended, a garden will quickly become a weed patch in which the weakly competitive garden plants are choked out and destroyed by the robustly productive weeds, most of which could be invasive species, resistant to herbicides or domestically poisonous, and with unknown economic value. A gardener’s only course of action is to spend a great deal of time and energy weeding the garden. This energy input is directly proportional to the “energy” inherent in the force of ecological succession. If you extrapolate this very small scale scenario to all of the agricultural fields and systems on Earth and visualize all of the activities of all of the farmers and gardeners who are growing our foods, and the natural forest ecosystem managers, you begin to get an idea of the immense cost in terms of time, fuel, herbicides and pesticides that humans pay every growing season because of the force of ecological succession. The natural forest ecosystem managers have to put in more time, knowledge and skills of Adaptive Resource Management in wake of global climate change.
I sincerely thank Professor Shem O. Wandiga, Professor Dan Olago and Professor Nicholas Oguge for having been my mentors and supervised my Doctoral research at the Institute of Climate Change and Adaptation (ICCA), University of Nairobi. They demonstrated profound knowledge about the complexities and dynamics encapsulate in the study of Global Climate Change. I wish to thank my co-author for the input.
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Whittaker, H. R. (1974). Climax Concepts and Recognition. Vegetation Dynamics pp 137-154 Posted on August 26, 2019Edit “An Overview of Impacts of Climate Change on Mountain Biota and Dependant Livelihoods: A Global Perspective with a Focus on Tropical Mountains”
An Overview of Impacts of Climate Change on Mountain Biota and Dependant Livelihoods: A Global Perspective with a Focus on Tropical Mountains
Kennedy W. Nyongesa1, Daniel O. Olago2, Nicholas O. Oguge2, Shem O. Wandiga2
1 Institute for Climate Change and Adaptation (ICCA), University of Nairobi 2 Institute for Climate Change and Adaptation (ICCA), University of Nairobi Corresponding Author Email: firstname.lastname@example.org
Mountains exhibit biological richness, their diversity of life zones and habitats leads to unique flora and fauna and to the exceptional cultural diversity of mountain people, making mountains especially important sites for conservation efforts and projects. Recent research shows that climate change will be more pronounced in high-elevation mountain ranges, which are warming faster than adjacent lowlands, and that the pace of climate zone shifts will be higher in such regions than in lowlands. This implies that mountain biota is particularly vulnerable to climate change. Mountain biodiversity provides ecosystem goods and services directly used by humans, including high elevation medicinal plants, mountain crops, timber and other montane forest products; it ensures a steady flow of clean water, provides an unpolluted and healthy environment for residents, and offers attractive landscapes for Eco-tourism. The benefits and the services provided by mountain biodiversity are huge, in economic, political and social terms hence the costs of losing the services provided by mountain vegetation are huge – both in ecological and economic terms. Mountain biodiversity also ensures the basis for the production of healthy food needed for expanding markets worldwide. Traditional indigenous communities often use and manage biodiversity in mountain-protected areas, and could be more threatened than biodiversity itself; thus, human interaction with regional species and climatic drivers has shaped mountain biodiversity for centuries. Local people should be encouraged towards stewardship of both their natural and cultural heritage. Participation of mountain communities at all stages is crucial in the sustainable management and use of biodiversity. This theoretical review paper gives an exposé of climate change related threats to the survival of mountain biodiversity and the human livelihoods that depend on it. In this paper, a conclusion is drawn and a conclusive working model in the context of Adaptive Resource Management is illustrated and discussed.
Key Words: Biodiversity, Climate Change, Impacts,Indicator Species, Livelihoods, Mountains
Biodiversity underpins the functioning of ecosystems on which humanity depends for food, water, health and other diversified facets of human livelihoods (Sinclair, 2003). The impacts of climate change on biodiversity can be observed around the world (Dawson et al., 2011; Cahill et al., 2012; CBD, 2009). Biota refers to the animal and plant life of a particular region, habitat, ecosystem or geological period.
The ecology of hoofed big-game species known as ungulates, in the northern Rocky Mountains of the United States of America, is strongly influenced by climate (Lawton & Gaston, 2001). Climate change impacts on summer precipitation, winter snow pack, and the timing of spring green-up, all of which control animal physiology, demography, diet, habitat selection and predator prey interactions. However, the degree of response to these impacts from animals such as elk, moose, mule deer, and pronghorn antelope is uncertain. Thus, impacts of climate change can not only directly impact ungulate species, but also the ability of managers to promote conservation through tourism; a direct hit on the economies of many states (Parmesan & Yohe 2003).
Not all species are affected by climate change equally due to the complex interaction of species within the ecosystem (Shilla, 2014). Species differ in size, genetic makeup and physiological requirements and functions that all together inform the behavior, life cycles, habits, habitats, diet, reproduction, geographical distribution and their response to environmental stressors including climate change stressors such as high temperatures and droughts (Tylianakis et al., 2008).
The overall vulnerability of species or ecological communities to climate change can be determined by assessing the relationship between three primary components: exposure, sensitivity, and adaptive capacity (Mawdsley et al., 2009). Exposure is the degree or magnitude of stress placed upon a species or habitat due to changing climate conditions or increased climate variability (IUFRO, 2009). This could be measured in relationship to direct climate effects like drought and heat stress. Exposure can also be assessed relative to indirect factors such as natural or man-made barriers to distribution and land-use changes in response to climate change. Sensitivity is the degree to which a species or habitat will be affected by or is responsive to climate change and variability (Hulme, 2005). For any given species, the level of sensitivity could relate to dispersal ability, physical habitat specificity, or temperature and precipitation requirements (Vie et al., 2009; Mawdsley and Lamb, 2013). Adaptive capacity is the potential or capability of a species or habitat to adjust to climate change as a means to moderate potential damages, take advantage of opportunities, or to cope with consequences (Hulme, 2005). Generally, the higher the adaptive capacity of an organism or wildlife habitat to the potential impacts of the threat, the lower the overall vulnerability (Glick et al., 2011).
Cernea and Schmidt-Soltau (2003) posit that there is already undeniable evidence that animals and plants are affected by climate change in both their distribution and behavior. Unless greenhouse gas emissions are severely reduced, climate change could cause a quarter of terrestrial animals, birdlife and plants to become extinct (IPCC, 2007). Climate change directly erodes natural capital, and thus the resource base for human enterprise (ACCESS/IUCN, 2014).
Impacts of Climate Change in Tropical Mountains on Human Communities
Mountains represent unique areas for the detection of climatic change and the assessment of climate-related impacts (Beniston, 2003; IMD, 2006).This view is supported by recent research on climate change in tropical mountain ecosystems and its implications on the mountain communities (ACCESS/IUCN 2014). Recent research shows that climate change will be more pronounced in high-elevation mountain ranges, which are warming faster than adjacent lowlands (World Bank, 2008; Macchi, 2011), and that the pace of climate zone shifts will be higher in such regions than in lowlands (Mahlstein et al., 2013). The mountain ecosystems in Africa appear to be undergoing significant observed changes that are likely due to complex climate-land interactions and climate change (IPCC, 2007). Research suggests that at least some of the world’s forested ecosystems may already be experiencing climate change impacts and raise concern that forests may become increasingly vulnerable to higher tree mortality rates and die-off in response to future warming and drought, even in environments that are not normally considered water limited (Allen et al., 2010; Sharma et al., 2010a).Warming and drying trends on Mt. Kilimanjaro have increased fire impacts, which have caused a 400-m downward contraction of closed (cloud) forest, now replaced by an open, dry alpine system (Hemp, 2005).
The tropical African climate is also favorable to most major vector-borne diseases, including: malaria, schistosomiasis, onchocerciasis, trypanosomiasis, filariasis, leishmaniasis, plague, Rift Valley fever, yellow fever and tick-borne haemorrhagic fevers (Githeko et al., 2000). The African continent has a high diversity of vector species complexes that have the potential to redistribute themselves to new climate-driven habitats leading to new disease patterns (ACCESS/IUCN, 2014); this relates not only to human health, but also to the health of all other groups or classes of living organisms, both in the animal and plant kingdoms (Nyongesa,Omuya and Sitati, 2016. There is growing scientific evidence that many mountain regions have become increasingly disaster-prone in recent decades (Sharma et al., 2010b), and are more frequently affected than other environments by destructive natural processes including earthquakes, volcanic eruptions, dam bursts or glacial lake outbursts, as well as avalanches and landslides (Kaltenborn, et al., 2010)).
Considerable loss of woodlands and forest cover due to deforestation and cultivation, particularly on steep concave slopes of the Mt. Elgon National Park in Uganda, has induced a series of shallow and deep landslides in the area during rainfall events (Mugagga et al., 2012). Globally, climate change is very likely to increase the pressure exerted by non-seismic hazards: casualties and damage due to hazards in mountain regions will increase irrespective of global warming, especially where populations are growing and infrastructure is developed at exposed locations (ACCESS/IUCN, 2014).
Vulnerability of Mountain Biodiversity and Human Livelihoods to Climate Change
Körner et al. (2010) observe that mountain vegetation secures watersheds from slope failure such as erosion, mudflows and avalanches. Mountain freshwater supplies, which are crucial for all downstream areas, greatly depend on stable and intact vegetation in catchments (Hamilton and McMillan, 2004); a highly structured, diverse ground cover with different root systems is probably the best insurance for slope stability and for securing railway lines, roads and settlements worth billions of dollars.
Hamilton and McMillan (2004) posit that the ongoing socio-economic changes cause a dramatic reduction in traditional land care and overexploitation of easily accessible terrain. In many regions of the world traditional mountain landscapes disappear, and with these the associated wild and domesticated species and breeds. Hamilton (2006) posits that from a development perspective, where poverty alleviation and improvement of livelihoods are core concerns, efforts thus need to be undertaken to preserve biological diversity as an important asset of mountain people. These are often characterized by a multitude of distinct societies and cultures that belong to the most disadvantaged and vulnerable rural communities to be found on earth (Baron et al., 2009). Traditional indigenous communities often use and manage biodiversity in mountain-protected areas, and may be even more threatened than biodiversity itself (Hamilton and McMillan, 2004); thus, human interaction with regional species and climatic drivers has shaped mountain biodiversity for centuries.
According to Hamilton and McMillan (2004), sub-tropical and tropical mountains offer striking examples of intensification of human pressure on montane areas, e.g. in African mountains, humans have traditionally settled in uplands, where the climate is mild and the environment relatively disease-free compared to the arid or very humid lowlands. However, more recently, increasing population pressure has led to unsustainable land practices and land use detrimental to biodiversity (Molg et al, .2012). Land use effects can be more dramatic than natural disasters or climatic change (Noroozi et al., 2008; Nyongesa et al,.2016).
Climate-Change Vulnerabilities of Africa’s Large Mammals
The threat of climate change has become an overwhelming concern in the field of wildlife conservation; projected changes in the world’s ecosystems are already being observed (Hulme et al., 2001). IPCC (2007) reports that these world’s ecosystem changes are occurring faster than expected in Africa, particularly in southern Africa. The numbers of mammal species in the national parks in sub-Saharan Africa could decline by 24% to 40% (IPCC, 2014). One study predicts that 66% of animal species in South Africa’s Kruger National Park could go extinct due to extreme droughts (Erasmus et al., 2002). A study in Namibia showed a positive correlation between the richness of large wildlife species and income from ecotourism and trophy hunting (Naidoo et al., 2011).
The vulnerability of a species to climate change is a factor of the extent of change to which it will be exposed, its sensitivity to the altered conditions and its ability to adapt (Glick et al., 2011); the adaptive capacity, or resilience, of a species depends upon its ability to tolerate and/or adjust to climate change. Reviews of climate change vulnerabilities for the African large mammals indicate that there are several key areas of vulnerability shared by many of these species (Hulme et al., 2001). Chief among these is the need for surface water. Many of the species are water-dependent, and many must drink daily. Some large mammals such as the African elephant and hippopotamus have enormous water requirements that can best be met by large bodies of water such as lakes and rivers (Naidoo et al., 2011). Heat stress is another common vulnerability shared across many of the African large mammal species (Maloiy et al., 2008). The lack of habitat connectivity has been mentioned as a contributing element to climate vulnerability in many of the African mega fauna species (Gaylard et al., 2009). Figure 1 shows the conceptual framework as contemplated in this paper. The framework exhibits the systems approach-transdisplinary display of the interdependence of concepts.
Figure 1: The Systems Approach-Transdisplinary display of the Interdependence of Concepts
Source: Nyongesa et al, 2019
The conceptual framework in this study depicts a concept map that shows the integration, interrelation, interaction and interdependence of climate change, vulnerability of indicator species to climate change impacts, the three complexities of transdisciplinarity, climate change scenarios on indicator species and policies and strategies to support adaptation mechanisms.
Indicator Species and Keystone Species in Ecosystems
The use of organisms to indicate the state of, and changes to the environment has numerous tried and tested applications (Lawton and Gaston, 2001). Amphibians are highly diverse in the Bale Mountains of Ethiopia and have been used as indicator species to climate change (Körner, 2004).The alpine and nival belts represent the only life zones on the globe that occur at all latitudes, although at different altitudes, which makes them very attractive for global comparisons of biodiversity and climate change effects (CBD, 2009). An ecosystem is a local or regional grouping of biotic and abiotic components functioning together (CBD, 2009). Ecologists have contributed concepts such as the balance of nature, the stability-diversity hypothesis, and chaos theories, some of which are undergoing revision as the science of ecology continues to develop (Tylianakis et al., 2008). According to Shilla(2014) indicator species are those that reveal evidence for, or the impacts of, environmental change. On the other hand keystone species refers to a species whose presence or absence determines the stability or instability of an ecosystem (Sinclair, 2003).
Studies have shown that losses of keystone species and indicator species in an ecosystem have had considerable impacts on the ecosystems, thus protecting these species against anthropogenic activities is imperative (Shilla, 2014); carnivores are considered as keystone species. Migratory bogong moths are a keystone species in the snowy mountains of Australia, as they are an important food source for a number of animals (Spehn et al., 2010); however, earlier snowmelt due to climate change is not being matched by earlier moth arrival, resulting in serious consequences for the endangered pygmy-possum.
The effects of climate change on plants shall affect all the food chain and food web dynamics in the mountain ecosystems because plants are the biological primary producers (Noroozi et al., 2008). Climate change impact models have suggested serious biodiversity losses, and have indicated that plants in mountain regions may be among those most affected (Körner and Spehn, 2002). Further, climate and land use often interact in ways that influence biodiversity, implying that these factors cannot be considered in isolation (ACCESS/IUCN, 2014) for example, land use may modify climatic impacts on species distributions by altering dispersal routes. Where land use creates barriers to dispersal for native species and facilitates dispersal for invasive species; climate change in human-dominated landscapes is likely to select for invasive species and against many native species (Sinclair, 2003). The responses of ecological systems to global climate change reflect the organisms that are within them (Barthlott et al., 2007); it is the responses of individual organisms that begin the cascade of ecological processes that manifest as changes in system properties, some of which feedback to influence climate and land use.
Impacts of Climate Change on Mountain Plant Species
According to Pohl et al. (2009), the world’s high mountain regions harbour a large number of highly specialized plant species that are governed by low-temperature conditions; climate warming may force many of these species towards ever higher elevations and finally to mountain-top extinction. Long term observation sites, therefore, are a crucial prerequisite for assessing the impacts of climate change in high mountain regions (Körner and Spehn, 2002). Large, slowly reproducing organisms such as the large mammals with small populations would be expected to be on the losing side (Barthlott et al., 2007). Not surprisingly, plant species in higher elevations that belong to a generalist group of weeds have an advantage (Noroozi et al., 2008).
Mutke and Barthlott (2005) observe that some late successional plant species, however, are so resilient that they have hardly been affected by climatic change. Others may escape problems by making use of the diverse mosaics of high elevation microhabitats (Körner et al., 2010). Usually, a temperature increase of 1–2°C exerts little short term change on alpine vegetation, due to the substantial natural inertia of high elevation plant species (Pohl et al., 2009); more pronounced warming is likely to bring substantial changes. Because each species responds individually, new assemblages are expected, rather than a migration of established communities. Changes in plant communities also imply changes in animal habitats (Noroozi et al., 2008). Especially for large mammal species with a narrow geographic and climatic range, the risk of extinction increases with climate warming (Vie et al., 2009).
Noroozi et al. (2008) observe that in the timeframe of climatic warming, the evolution of new taxa is very unlikely. New adapted communities usually assemble by replacement of species by other species migrating into the community from lower elevations. When neither acclimation nor behavioral changes match the new demands, migration becomes inevitable, and in cases, where migration is not possible, species will disappear, at least locally. Körner et al. (2010) posit that species with a higher risk of vulnerability given the rapidity of climate change include: large territorial animals, late successional plant species (K-strategists), species with small restricted populations, and species confined to summits or the plains. Barthlott et al. (2007) emphasize that species with a lower risk of vulnerability to climate change include: small highly mobile organisms, ruderal plant species (r-strategists), widespread species with large populations and mid-slope species
Adaptive Management and Land Use Changes in view of Climate Change
Adaptive Management (AM), also known as Adaptive Resource Management (ARM), is a structured, iterative process of robust decision making in the face of uncertainty, with an aim to reducing uncertainty over time via system monitoring (Habron, 2003); in this way, decision making simultaneously meets one or more resource management objectives and, either passively or actively, accrues information needed to improve future management. Adaptive management is a tool which should be used not only to change a system, but also to learn about the system (Stankey et al., 2005). Bunnell et al. (2007) posit that because adaptive management is based on a learning process, it improves long-term management outcomes; the challenge in using the adaptive management approach lies in finding the correct balance between gaining knowledge to improve management in the face of relentless global climate change.
In fact, one-third (32%) of all protected areas, regardless of status and size, is in mountains, including 88 World Heritage Natural Sites, and 40% of all UNESCO Man and Biosphere Reserves(MAB) (Körner, 2009). The total number of mountain protected areas is 21,400 km2, on a total area of 5,996,075 km2 (World Bank, 2008). Climate change will definitely increase risk since expected increases of heavy rainfall, heat waves, and glacier melt will amplify hazards in many mountains worldwide, and in areas where they have not been known in the past (Hamilton and McMillan, 2004). In a study in eastern Uganda covering part of Mount Elgon, it was observed that over 90% of the households have attempted changing their farming operations in response to climate variability and extremes (Kansiime, 2012).
Desk top studies indicate that land use planning strategies are an important part of Adaptive Resource Management (ARM) in response to mitigating, adapting and preparing for climate change (Wolf and Moser, 2011); in many ways, land use planning is a valuable tool for responding to the effects of climate change due to its broad scope of application and relative flexibility as a mechanism for controlling land use and development. However, there can also be numerous challenges and barriers in applying land use planning instruments to address climate change issues and in considering climate change projections when formulating and applying land use planning measures (Habron, 2003). According to Körner et al. (2010), global climate change is often perceived as human-induced modifications in climate, indeed human activities have undeniably altered the atmosphere, and probably the climate as well.
At the same time, most of the world’s forests have also been extensively modified by human use of the land (Habron, 2003); thus, climate and land use are two prongs of human-induced global change and the organisms within forests mediate the effect of these forces on forests. Consideration of climate, land use and biodiversity is key to understanding forests ecosystems response to global climate change (Körner et al., 2010).
Indigenous Ecological Knowledge (IEK) about peoples’ environment including weather and climate suggests not only that knowledge passed down through generations is still used today but that it can complement scientific knowledge and potentially help to adapt to faster changes than would be associated with variability alone (Wolf and Moser, 2011). In the Himalayas, for example, it has been noted that there is very little literature on the impacts or the response of the communities, yet there is a wealth of information in the form of local knowledge of the indigenous communities based on their observations, perceptions and experiences over the years that can be effectively utilized to complement scientific data to improve climate change mitigation and adaptation strategies (Ingty and Bawa, 2012).
Indigenous Ecological Knowledge (IEK) could be used to design sustainable conservation strategies while complementing scientific data. The changing climate has made the existing conservation approaches to become increasingly unreliable partly because of the lag in adoption of Adaptive Resource Management (ARM) approaches by managers. Figure 2 shows the Conclusive Working Model as envisaged in this paper.
Figure 2: The Inter-link between Mountain Biota,Global Climate Change Impacts,Dependant Human Livelihoods and the resultant Development Activities
Source: Nyongesa et al, 2019
The Conclusive Working Model in this paper illustrates that there is a feedback relationship between mountain biota and dependent human livelihoods together with the resultant development activities. The biota and the ecosystems in which they are habituated provide ecological services to the mountain people, which enable them to make development activities. For peoples’ livelihoods to be sustainable they have to be involved in the conservation of the biota at all stages especially with the help of Indigenous Ecological Knowledge (IEK) complementing Scientific Data to have the resultant Adaptive Resource Management (ARM). Climate change has impacts on both the mountain biota and human livelihoods, hence for effective resilience and adaptation mountain biota and dependent human livelihoods must have mutual facilitation for each other.
I thank my supervisors who took me through my Doctorate research work and for their unequivocal mentorship. These are Prof. Shem O. Wandiga,Prof.Daniel O. Olago andProf. Nicholas O. Oguge who also co-authored this work.
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By Kennedy W. Nyongesa
“Global warming…doesn’t that have something to do with the ozone?” Well, no. Environmental issues are not all the same. It’s common for people to confuse climate change and ozone depletion, but they are separate issues – although they are indirectly connected in some interesting ways.
Ozone, which is made of three oxygen atoms stuck together (instead of two, which is what normal oxygen gas is made of), is vital to life on Earth. It forms a layer in the stratosphere, the second layer up in the atmosphere, that is very good at absorbing ultraviolet (UV) radiation from the Sun. UV radiation severely damages organisms if enough of it reaches the surface. The 3% or less that gets through the ozone already gives us sunburns and skin cancer, so you can imagine what the situation would be like if the ozone layer wasn’t there at all.
In the middle of the 20th century, synthetic gases known as chlorofluorocarbons (CFCs) became popular for use in refrigerators and aerosol products, among other applications. They were non-toxic, and did not react easily with other substances, so they were used widely. However, their chemical stability allowed them to last long enough to drift into the stratosphere after they were emitted.
Once in the stratosphere, the CFCs were exposed to UV radiation, which was able to break them down. Free chlorine atoms (Cl) were liberated, a substance that is very reactive indeed. In fact, Cl acts as a catalyst in the decomposition of ozone, allowing two ozone molecules to become three oxygen molecules, losing their UV absorbing power in the process. Since catalysts are not used up in a reaction, the same Cl radical can continue to destroy ozone until it reacts with something else in the atmosphere and is removed.
Over the poles, the stratosphere is cold enough for polar stratospheric clouds (PSCs) to form. These PSCs provided optimum conditions for the most reactive chlorine gas of all to form: ClO (chlorine monoxide). Now there wasn’t just a catalytic cycle of free Cl radicals depleting the ozone, there was also a cycle of ClO. It turns out that Antarctica was more favourable for ozone depletion than the Arctic, both because its temperatures were lower and because its system of wind currents prevented the ozone-depleting substances from drifting out of the area.
Before long, there was a hole in the ozone layer over Antarctica (due to the PSCs), and concentrations were declining in other locations too (due to the basic Cl reactions). The issue became a frontier for scientific research, and scientists Crutzen, Rowland, and Molina won the 1995 Nobel Prize in Chemistry for their work with atmospheric ozone.
In 1987, politicians worldwide decided to ban CFCs under the Montreal Protocol. This movement was largely successful, and the use of CFCs has become nearly negligible, especially in developed nations. They have been replaced with gases that safely decompose before they reach the stratosphere, so they don’t interfere with ozone. The regulations are working: the ozone hole in Antarctica has stabilized, and global stratospheric ozone concentrations have been on the rise since 1993.
In contrast, climate change is a product of greenhouse gases such as carbon dioxide. Unlike CFCs, most of them are not synthetic, and they are released from the burning of fossil fuels (coal, oil, and natural gas), not specific products such as refrigerators. Rather than destroying a natural process, like CFCs do, they strengthen one to the point of harm: the greenhouse effect. This phenomenon, which traps heat in the atmosphere, is absolutely vital, as the Earth would be too cold to support life without it. Increasing the concentrations of greenhouse gases with fossil fuels becomes too much of a good thing, though, as the greenhouse effect traps more heat, warming the planet up.
Just a few degrees Celsius of warming can cause major problems, as agricultural zones, wind and ocean currents, and precipitation patterns shift. The sea level rises, submerging coastal cities. Many species go extinct, as the climate changes faster than they can adapt. Basically, the definition of “normal” in which our civilization has developed and thrived is changing, and we can’t count on that stability any more.
Unlike the Montreal Protocol, efforts to reduce greenhouse gas emissions have more or less failed. Fossil fuels permeate every part of our lives, and until we shift the economy to run on clean energy instead, convincing governments to commit to reductions will be difficult at best. It remains to be seen whether or not we can successfully address this problem, like we did with ozone depletion.
Although these two issues are separate, they have some interesting connections. For example, PSCs form in cold areas of the stratosphere. That’s why the ozone hole is over Antarctica, and not somewhere else. Unfortunately, global warming is, paradoxically, cooling the stratosphere, as a stronger greenhouse effect means that less heat reaches the stratosphere. Therefore, as climate change progresses, it will make it easier for the ozone depletion reactions to occur, even though there are fewer CFCs.
Additionally, CFCs are very strong greenhouse gases, but their use has drastically reduced so their radiative effects are of lesser concern to us. However, some of their replacements, HFCs, are greenhouse gases of similar strength. They don’t deplete the ozone, but, per molecule, they can be thousands of times stronger than carbon dioxide at trapping heat. Currently, their atmospheric concentrations are low enough that they contribute far less forcing than carbon dioxide, but it wouldn’t take a large increase in HFCs to put us in a bad situation, simply because they are so potent.
Finally, these two issues are similar in that ozone depletion provides a smaller-scale analogue for the kinds of political and economic changes we will have to make to address climate change:
- Unintended chemical side effects of our economy posed a serious threat to all species, including our own.
- Industry representatives and free-market fundamentalists fought tooth and nail against conclusive scientific findings, and the public became bewildered in a sea of misinformation.
- Governments worked together to find sensible alternatives and more or less solved the problem.
By Kennedy W. Nyongesa
Ozone affects climate, and climate affects ozone. Temperature, humidity, winds, and the presence of other chemicals in the atmosphere influence ozone formation, and the presence of ozone, in turn, affects those atmospheric constituents.
Interactions between ozone and climate have been subjects of discussion ever since the early 1970s when scientists first suggested that human-produced chemicals could destroy our ozone shield in the upper atmosphere. The discussion intensified in 1985 when atmospheric scientists discovered an ozone “hole” in the upper atmosphere (stratosphere) over Antarctica. Today, some scientists are predicting the stratospheric ozone layer will recover to 1980 ozone levels by the year 2050. These scientists say we can expect recovery by that time because most nations have been abiding by international agreements to phase out production of ozone-depleting chemicals such as chlorofluorocarbons (CFCs) and halons. But the atmosphere continues to surprise us, and some atmospheric scientists recently demonstrated a new spin on the ozone recovery story that may change its ending. Well before the expected stratospheric ozone layer recovery date of 2050, ozone’s effects on climate may become the main driver of ozone loss in the stratosphere. As a result, ozone recovery may not be complete until 2060 or 2070.
Ozone’s impact on climate consists primarily of changes in temperature. The more ozone in a given parcel of air, the more heat it retains. Ozone generates heat in the stratosphere, both by absorbing the sun’s ultraviolet radiation and by absorbing upwelling infrared radiation from the lower atmosphere (troposphere). Consequently, decreased ozone in the stratosphere results in lower temperatures. Observations show that over recent decades, the mid to upper stratosphere (from 30 to 50 km above the Earth’s surface) has cooled by 1° to 6° C (2° to 11° F). This stratospheric cooling has taken place at the same time that greenhouse gas amounts in the lower atmosphere (troposphere) have risen. The two phenomena may be linked.
Says Dr. Drew Shindell of the NASA Goddard Institute for Space Studies (GISS), “I’ve long been aware that chemistry and climate influence one another strongly. I started to ask how cold the stratosphere might get because of increasing amounts of greenhouse gases. I was wondering whether or not the cooling in the stratosphere would be rapid enough that more ozone depletion would take place than we had previously calculated. Would the cooling be so fast that even more ozone depletion would occur before the impact of international agreements to limit ozone had time to take effect?” This would create a possible feedback loop. The more ozone destruction in the stratosphere, the colder it would get just because there was less ozone. And the colder it would get, the more ozone depletion would occur.
The deepest ozone losses over both the Arctic and the Antarctic result from special conditions that occur in the winter and early spring. As winter arrives, a vortex of winds develops around the pole and isolates the polar stratosphere. When temperatures drop below -78°C (-109°F), thin clouds form of ice, nitric acid, and sulphuric acid mixtures. Chemical reactions on the surfaces of ice crystals in the clouds release active forms of CFCs. Ozone depletion begins, and the ozone “hole” appears. In spring, temperatures begin to rise, the ice evaporates, and the ozone layer starts to recover.Hello world!
Reflections on a Possible Delay
The concept that stratospheric cooling due to ozone loss may lead to a delay in recovery of the ozone layer has fallen on fertile ground. Scientists running different kinds of global models are finding similar results. “That gives us confidence,” says Dr. Venkatachalam Ramaswamy, at NOAA’s Geophysical Fluid Dynamic Laboratory. “We’re confident in our assessment, because the models can help us to understand the observed ozone and temperature changes on a global scale.”
Stratospheric cooling may have been taking place over recent decades for a number of reasons. One reason may be that the presence of ozone itself generates heat, and ozone depletion cools the stratosphere. Another contributing factor to the cooling may be that rising amounts of greenhouse gases in the lower atmosphere (troposphere) are retaining heat that would normally warm the stratosphere. However, scientists hold varying degrees of conviction about the nature of the link between tropospheric warming and stratospheric cooling. “The warming of the troposphere and its potential influence upon the stratospheric circulation is an important consideration,” points out Ramaswamy, “though the quantitative linkages are uncertain. It is possible that they may be interdependent only in a tenuous manner.”
“The problem is that we haven’t had adequate data,” Ramaswamy continues. “Observations have been primarily limited to only a very few locations in the stratosphere. We have only 20 years of full global coverage from satellites. Of course radiosonde goes back 40 years but that is not global coverage.”
Jim Hansen, of NASA’s Goddard Institute for Space Studies, agrees with Ramaswamy on the need for data. “Climate forcing by ozone is uncertain because ozone change as a function of altitude is not well measured. Especially at the tropopause (where the troposphere meets the stratosphere), we don’t know enough. The climate system is highly sensitive, especially to changes in the tropopause region. We need exact temperatures and ozone profiles at different altitudes and around the globe.” Hansen and others look forward to the launch of NASA’s Aura satellite in 2004. A vital part of NASA’s Earth Observing System, Aura will observe the composition, chemistry and dynamics of the Earth’s upper and lower atmosphere, including temperatures and ozone amounts. “What Aura will give us is quite exciting. There will be a suite of instruments measuring in regions not well measured before,” says Hansen.
In spite of large uncertainties that remain, scientists express a sense of accomplishment with their achievements so far. “I think one of the successes has to be the fact that we can now explain the observed temperature trends in the stratosphere reasonably well, states Ramaswamy. “There is actually a very strong indication that the observed changes in radiative and chemical species are responsible for globe-wide cooling of the stratosphere.”
The Variable Arctic
Although many global scale models agree with each other and with observations on the future of ozone recovery, most regional scale models do not agree. Atmospheric models show that the cooling influence of ozone depletion accounts very well for observed cooling winter-time temperature trends in the Antarctic, but not in the Arctic.
Differences among regions make predictions about complex atmospheric chemistry problematic. The Arctic and Antarctic regions, where low stratospheric ozone amounts are of great concern, differ in significant ways. The complex topography of the high latitude Northern Hemisphere, with its distribution of land masses and oceans, makes the Arctic atmosphere more dynamic and variable.
The Antarctic is colder than the Arctic. Antarctic winds form a relatively stable vortex for long periods of time, and the vortex allows temperatures of the air trapped within it to get extremely low. Shindell explains, “In the south, air masses just sit over the pole and get colder.”
Such stability makes the Antarctic somewhat more predictable than the Arctic. Shindell says, “It’s so variable in the Arctic that we have to have better data to figure out what we should believe and what we can have confidence in for the future.”
These coastal mountains in southeast Alaska are representative of the rugged terrain of the Northern Hemisphere’s high latitudes. High mountains and the contrast between large continental landmasses and open ocean in the Northern Hemisphere disturb the air over the Arctic, preventing the formation of a stable circulation pattern. In part, it is the lack of a stable “polar vortex” that prevents the Arctic from experiencing the extremely cold temperatures and dramatic ozone loss seen above Antarctica. In spite of this, large ozone losses occurred in the Arctic during the last several years. (Photograph courtesy NOAA Photo Library)
Although dramatic ozone depletion did not occur in the Arctic in the 1980s when it occurred in the Antarctic, times are changing. Very large ozone losses have occurred in the Arctic recently, especially in the late 1990s. Ozone chemistry is very sensitive to temperature changes. Since temperatures in the Arctic stratosphere often come within a few degrees of the threshold for forming polar stratospheric clouds, further cooling of the stratosphere could cause these clouds to form more frequently and increase the severity of ozone losses.
The Arctic may be changing in another way that differs from the Antarctic. With stratospheric cooling, the differences in temperature between the stratosphere and the troposphere are increasing. Differences in temperature creates winds, so stratospheric wind speeds have been increasing. (The Antarctic isn’t affected by increasing greenhouse gases like the Arctic is because it’s colder, and the polar wind circulation over the Antarctic is already very strong.)
Shindell says that from both observations and models, he has found increasing wind speeds not only at high altitudes but also near the surface. “That’s a large effect on climate,” he points out. “Changes in stratospheric ozone and winds affect the flow of energy at altitudes just below, which then affect the next lower altitudes, and so on all the way to the ground. That would be the most intriguing aspect of all this, though it’s still controversial.”
Ozone and Climate at the Surface
Interactions between ozone and climate naturally occur not only in the stratosphere, but also at the Earth’s surface (troposphere). There are known chemical and physical aspects of ozone formation we can watch carefully as climate changes. Ozone forms in the troposphere by the action of sunlight on certain chemicals (photochemistry). Chemicals participating in ozone formation include two groups of compounds: nitrogen oxides (NOx) and volatile organic compounds (VOCs). In general, an increase in temperature accelerates photochemical reaction rates. Scientists find a strong correlation between higher ozone levels and warmer days. With higher temperatures, we can expect a larger number of “bad ozone” days, when exercising regularly outdoors harms the lungs. However, ozone levels do not always increase with increases in temperature, such as when the ratio of VOCs to NOx is low.
As the troposphere warms on a global scale, we can expect changes in ozone air quality. Generally speaking, warming temperatures will modify some but not all of the complex chemical reactions involved in ozone production in the troposphere (such as those involving methane). Because of the short-lived nature of these chemical constituents and variations across space and time, the uncertainty is too large to make predictions. Scientists can only speculate about specific kinds of change, about the direction of change in a particular location, or about the magnitude of change in ozone amounts that they can attribute to climate.
Some speculation involves VOC emissions from natural biological processes. Certain kinds of plants such as oak, citrus, cottonwood, and almost all fast-growing agriforest species emit significant quantities of VOCs. Higher temperatures of a warming climate encourage more plant growth, and therefore higher levels of VOCs in areas where VOC-emitting plants grow abundantly. Soil microbes also produce NOx. Soil microbial activity may also increase with warmer temperatures, leading to an increase in NOx emissions and a consequent increase in ozone amounts.
A warming climate can lead to more water vapor in the lower atmosphere, which would tend to produce more ozone. But cloud cover can also diminish chemical reaction rates because of reduced sunlight and therefore lower rates of ozone formation. Monitoring and analyzing such interactions is the best way we can improve our predictive capabilities. (Photograph courtesy Jeannie Allen, NASA GSFC/SSAI)
Another impact of climate on ozone pollution in the troposphere arises from the probability that higher temperatures will lead to greater demand for air conditioning and greater demand for electricity in summer. Most of our electric power plants emit NOx. As energy demand and production rises, we can expect amounts of NOx emissions to increase, and consequently levels of ozone pollution to rise as well.
Water vapor is also involved in climate change. A warmer atmosphere holds more water vapor, and more water vapor increases the potential for greater ozone formation. But more cloud cover, especially in the morning hours, could diminish reaction rates and thus lower rates of ozone formation.
Understanding the interactions between ozone and climate change, and predicting the consequences of change requires enormous computing power, reliable observations, and robust diagnostic abilities. The science community’s capabilities have evolved rapidly over the last decades, yet some fundamental mechanisms at work in the atmosphere are still not clear. The success of future research depends on an integrated strategy, with more interactions between scientists’ observations and mathematical models. Search for:
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