5. Ecosystem limits


Climate Change and Biodiversity Conservation



Human civilizations and the natural ecosystems that we know today have evolved to be well adapted to the current climate, which has been relatively stable during the last 7,000 years. Thus we can be confident that dangerous interference with the climate system would be prevented only if greenhouse gas concentrations could be returned to pre­industrial levels (i.e. 280 parts per million of CO2, 700 parts per billion of CH4, 270 parts per billion of nitrous oxide (N2O), zero parts per trillion of CFCs, HFCs, and PFCs). As stabilization of greenhouse gas concentrations at these levels does not appear to be feasible during at least the next century, the risk of adverse impacts from climatic change cannot be completely avoided. Furthermore, the risks of severe negative impacts and undesirable synergistic effects will grow if concentrations are allowed to increase further.


Scientists have begun to identify several key principles that can be used in assessing potential ecosystem vulnerability to climate change. For example, it can be said with some certainty that:



  • The faster the rate of climatic change, the higher the probability of substantial disruption of ecosystem structure and function, and surprise within natural ecosystems, and the greater the risk of serious ecosystem degradation.

  • Ecosystems will not react wholesale in response to climate change. Rather, each species will respond differently. Existing species associations will break up and new communities of plants and animals will take their place.

  • Ecosystem response to climate change will depend largely on competition between species to maintain themselves in new geographic areas or under changing conditions. In many cases, species such as pests, parasites, and opportunists will benefit.

  • Ecosystems already stressed by human activities will be more vulnerable to climatic threats and among the first to show the effects of climate change. However, the multiple factors affecting these ecosystems will complicate the identification of strictly climatic effects.

  • Species' adaptive abilities depend not only on genetic variability but also on dispersal and migration capacity. Ecosystem resilience and genetic variability within populations are being reduced through habitat fragmentation. They will be further reduced by pressures resulting from human­induced climate change.

  • For many ecosystems, increases in the frequency and severity of extreme weather events such as drought, storms, and floods, and changes in their geographic distribution, will lead to some of the most serious impacts. Changes in seasonal precipitation patterns and weather variability will also be critical. These changes are likely under any climate change scenario.




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