Working Group II: Impacts, Adaptation and Vulnerability

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Recent estimates indicate that 25% of the world's mammals and 12% of birds are at significant risk of global extinction. Climate change is only one of a long list of pressures on wildlife. Other pressures include exploitation of animals, pollution and other biochemical poisonings, extreme climatic events, wildlife diseases, collisions with towers and other structures, anthropogenic barriers to dispersal, and war and other civil conflicts. Alone or in combination, these pressures will greatly increase species' vulnerabilities to rarity and extinction (high confidence). Habitat conversion and degradation affect nearly 89% of all threatened birds and 83% of all threatened mammals. About one-fifth of threatened mammals in Australia and the Americas and the world's birds are affected by introduced species.

Impacts, Adaptations, and Vulnerabilities
  • Many animals already may be responding to local climatic changes. The types of changes already observed include poleward and elevational movement of ranges, changes in animal abundance, changes in body size, and shifts in the timing of events, such as earlier breeding in spring. Possible climatically associated shifts in animal ranges and densities have been noted on many continents and within each major taxonomic group of animals (see Table 5-3).
  • Laboratory and field studies have demonstrated that climate plays a strong role in limiting species' ranges (high confidence). Even though only a small fraction of all species have been monitored long enough to detect significant trends, changes exhibited over the past few decades in the bulk of these species are consistent with local warming and expected physiological responses (medium confidence). However, possible specific changes in wildlife from climate change can be projected only with low confidence for most species because of many possible contributing factors, such as habitat destruction and introduction of exotic species. Some species clearly are responding to global change (see Section 5.4.3), and many more changes probably have gone undetected. Researchers are in the process of coupling these discernible changes with various biological theories regarding climate and species spatial and temporal patterns; through this process, we expect that reliable general projections can be and in fact are being made.
  • Protecting threatened and endangered species requires measures that, in general, reverse the trend toward rarity. Without management, rapid climate change—in conjunction with other pressures—is likely to cause many species that currently are classified as critically endangered to become extinct and several labeled endangered or vulnerable to become much rarer, and thereby closer to extinction, in the 21st century (high confidence).
  • Concern over species becoming rare or extinct is warranted because of the goods and services provided by ecosystems and the species themselves. Most of the goods and services provided by wildlife (e.g., pollination, natural pest control) are derived from their roles within systems. Other valuable services are provided by species contributing to ecosystem stability or to ecosystem health and productivity. The recreational value (e.g., sport hunting, wildlife viewing) of species is large in market and nonmarket terms. Species loss also could impact the cultural and religious practices of indigenous peoples around the world. Losses of species can lead to changes in the structure and function of affected ecosystems and loss of revenue and aesthetics. Understanding the role each species plays in ecosystem services is necessary to understand the risks and possible surprises associated with species loss. Without this information, the probability of surprises associated with species loss is high (medium confidence).
  • Humans may need to adapt not only in terms of wildlife conservation but also to replace lost ecological services normally provided by wildlife. It may be necessary to develop adaptations to losses to natural pest control, pollination, and seed dispersal. Although replacing providers of these services sometimes may be possible, the alternatives may be costly. Finding replacements for other services, such as contributions to nutrient cycling and ecosystem stability/ biodiversity, are much harder to imagine. In many cases, such as the values of wildlife associated with subsistence hunting and cultural and religious ceremonies, any attempt at replacement may represent a net loss. In many countries, climate change impacts, such as reductions in wildlife populations, may have the greatest impact on the lowest income groups—those with the least ability to adapt if hunting opportunities decline.

Most rangelands in the world have been affected by human activity, and many are degraded in some way. Desertification tends to be associated with land degradation in rangelands; however, desertification combines many land degradation processes and can be exacerbated by climate change. Many of the rangelands of the world are affected by ENSO events and are sensitive to the frequency of these events, resulting in changes in productivity of these systems.

Impacts, Adaptations, and Vulnerabilities
  • Based on observations and modeling studies, the effects of elevated CO2 and climate change could result in increased plant productivity and thus an increase in soil carbon sequestration in many rangelands. However, some of the gains in productivity would be offset by increases in temperatures and by human management activities (medium confidence).
  • Modeling studies and observations suggest that plant production, species distribution, disturbance regimes (e.g., frequencies of fires, insect/pest outbreaks), grassland boundaries, and nonintensive animal production would be affected by potential changes in climate and land use. The impacts of climate change are likely to be minor compared to those of land degradation (high confidence).
  • Irrigation in semi-arid climates is a major cause of secondary salinization. Elevated CO2 may reduce the impacts of secondary salinization, although experimental work shows that any increase in temperature may negate these benefits and may even exacerbate problems of secondary salinity (medium confidence).
  • In many parts of the world that are dominated by rangelands, lack of infrastructure and investment in resource management limits available options for adaptation and makes these areas more sensitive and vulnerable to the impacts of climate change (high confidence). Some adaptation options (e.g., integrated land management) could be implemented irrespective of technology and infrastructure. Other adaptation options could be implemented through active involvement of communities in the management of rangelands.

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