A Concept Map of Impacts of Climate Change on Ecological Succession and Climax Communities:

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: kennyongesa@yahoo.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 equallyTherefore, 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.

Literature Review

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.

Theoretical Analysis

Some specific examples of ecological succession observable in tropical and temperate regions include:

  1. 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.
  2. 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.
  3. 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 Map

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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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: kennyongesa@yahoo.com


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).

Literature Review

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.

Theoretical Analysis

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 and Prof. Nicholas O. Oguge  who also co-authored this work.


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Ozone Depletion and Climate Change

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:

  1. Unintended chemical side effects of our economy posed a serious threat to all species, including our own.
  2. Industry representatives and free-market fundamentalists fought tooth and nail against conclusive scientific findings, and the public became bewildered in a sea of misinformation.
  3. Governments worked together to find sensible alternatives and more or less solved the problem.

We’ve already seen the first two events happen with climate change. Will we see more.

The Science of Ozone and Climate Change

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.