Impacts of Climate Change on Agro-Ecosystems and Food Security in Africa. A Review.

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 

This paper was presented at the 11th Egerton University Conference and Peer- reviewed, corrected and recommended for publication : Dates: 29 – 31 March, 2017 “Knowledge and Innovation for Social and Economic Development. ”


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.

Literature Review

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
1997 2003 2008 1997 2003 2008
small farms 13 10 15 5 10 10
medium farms 10 25 30 10 10 10
large farms and plantations 5 15 35 0 15 35
traditional brokers/wholesalers 70 45 10 70 40 10
imports 2 5 10 15 25 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).

Theoretical Analysis

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, Kitale National Polytechnic, Department of Mathematics and Applied Science :Corresponding


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.


Historical Overview

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:

  1. Direct impacts

Health and safety consequences of heat waves, floods, extreme weather events, increased concentrations of air pollutants.

  1. 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).

  1. 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.

  1. 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.

  1. 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
  2. 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.

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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