2. The ecological impacts of climate change


Climate Change and Biodiversity Conservation



That human­induced climatic change does indeed pose a major threat to biodiversity has been known for more than a decade. Several wide­ranging reviews published during that time have tried to take stock of the range of potential impacts across the globe. WWF is working to develop a strong scientific basis for understanding the potential impacts on wildlife and ecosystems. A first step is to identify those biomes and ecosystems that may be most sensitive to climate change. Most vulnerable will be those habitats where the first impacts are likely to occur, where the most serious adverse effects may arise, or where the least adaptive capacity exists. Table 1 gives an overview of these "front line" ecosystems and some of the climatic variables that influence them.



Table1. Most sensitive ecosystem types and climatic variables most likely to influence them


Biome, ecosystem, or landscape type

Key climate variables

Mangroves

Relative rate of sea-level rise
Storm frequency and severity


Coral Reefs

Relative rate of sea-level rise
Storm frequency and severity
Sea-surface temperature


Coastal marshes

Relative rate of sea-level rise
Storm frequency and severity


Tropical Montane Forest

Cloud cover and sunlight hours
Hurricane frequency and severity
Drought frequency and annual rainfall distribution


Raised peat bogs

Mean summer temperature
Mean annual precipation


Alpine/Mountains

Mean annual temperature
Snow fall and melt
Growing season length


Boreal forest

Mean annual temperature
Fire frequency and severity
Storm frequency and severity
Growing season length


Arctic

Mean annual temperature
Season length
Precipitation
Timing and extent of ice melt


Low-lying islands

Relative sea-level rise
Storm frequency and severity


Arid and semi-arid areas

Precipitation patterns
Minimum winter temperatures





For some ecosystems, such as coral reefs and tropical forests, climate change is presently a low­level threat in comparison with current environmental pressures and degradation. In coming decades, as habitats decline and become more fragmented, and their communities less diverse, there is every likelihood that the rate of climate change will increase. As natural systems lose their resilience, the threat of climatic impacts will become more acute, and act as a cumulative stressor in addition to pre­existing problems. Much of today's discussion about climate change centres on predicting what could happen to today's ecosystems over the course of a few years or decades. However, an even longer­term view is required if biological diversity is to be protected for generations to come.


Most ecological impact studies have suffered from four central problems:



  • Lack of reliable regional climate change scenarios and information about changes in weather variability and seasonality

  • Lack of long­term ecological data sets


  • Major gaps in current scientific understanding of community and population ecology

  • The difficulty of differentiating climate change impacts from other stress­related environmental degradation.



These barriers to knowledge are typical of those confronting scientists in dealing with any complex set of problems. The difference in the case of climate change is that policy­makers urgently require some indication of the probability of damage to ecosystems in order to guide their actions in planning to reduce future levels of pollution. At the "Earth Summit" of 1992 in Rio de Janeiro more than 150 countries signed the UNFCCC and committed themselves to meeting its objectives. The wording of the convention specifically rules out lack of scientific certainty as a reason for inaction. Indeed, conservation biologists have long­known that uncertainty as to how ecosystems react to environmental pressures dictates the adoption of the the most conservative and broad­ranging protection strategies. It is simpler to plan conservation when the threats are clearly defined and easily predictable. Climate change impacts at the level of individual ecosystems are still highly unpredictable, and therefore present the kind of danger that requires increased conservation commitment. In the case of climate change, the most effective strategy to protect biodiversity will be a parallel approach which seeks both to reduce greenhouse gas emissions, and to increase the resilience of natural ecosystems through better management and protection.




Degraded natural ecosystems will be more vulnerable to climate change



Scientists, therefore, must endeavour to provide the best available information to policy­makers and help provide them also with some of the tools to analyse its policy implications. One of the tools they require is a methodology for assessing the meaning of the phrase used in Article 2 of the convention which outlines the major objective of controlling greenhouse gas emissions in order to allow "ecosystems to adapt naturally" to change. This begs the question how much climate change is too much?




The climate is likely to change so fast that many species will be unable to adapt in time



Some scientists have suggested that a total increase in global annual average temperature of 2°C, or a rate of change of 0.1°C a decade should be set as targets under the convention in order to protect nature. But even these targets (which would be substantially exceeded under current emissions projections) could not prevent significant damage to many ecosystems. For most species, any change in average climatic conditions will have some, often negative, impact. If ecosystem protection is a genuine objective of the Climate Convention, then climate change targets should aim to cap warming at no more than 1°C and at a rate of less than 0.01°C a decade (see also `Temperate and boreal forests' on page 12). Any greater change will undoubtedly have severe negative impacts and cause irreversible alterations in our planet's natural habitats.


It is difficult to define natural adaptation. Instances of change need to be related directly to human activity. Generalized trends over geological time can be relatively easily identified in this way. For example, the changes in distribution of various tree species between glaciations can be linked to natural, long­term variations in the Earth's climate. The creation of Britain's wildwood by the spread, over thousands of years, of birch, then oak, alder, and other tree species into moorland and tundra after the last glaciation was natural adaptation to natural climate change. However, the deforestation that destroyed approximately half of the climax vegetation between 4000 BC and 500 BC was largely caused by human development and agriculture. Species have evolved to cope with natural climate changes in the absence of human interference. It is doubtful that in a world under pressure from human development and agriculture they will be so successful in adapting to rates of climate change that will be at least an order of magnitude faster than at any time in the last 10,000 years and possibly the last 100,000 years.




Back to the previous page

Copyright 1996, The World Wide Fund For Nature