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"High Confidence" About Impacts
Working Group II's contribution to the IPCC's fourth assessment, issued on April 6, 2007, expressed "high confidence" that climate change is affecting natural and hydrological systems worldwide. (WGII Summary for Policymakers/SfP, page 8)
These documented impacts include:
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Enlargement and growing numbers of glacial lakes. (WGII SfP, page 8)
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Increased ground instability in permafrost regions and avalanches in mountains. (WGII SfP, page 8)
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Changes in some Arctic and Antarctic ecosystems, as well as predators high in the food chain. (WGII SfP, page 8)
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Increased run-off and spring flows in many glacier- and snow-fed rivers. (WGII SfP, page 8)
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Warming of lakes and rivers in many regions. (WGII SfP, page 8)
The authors expressed "very high confidence" in documented effects on terrestrial biological systems, such as:
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Earlier spring events such as leaf unfolding, bird migration and egg-laying. (WGII SfP, page 8)
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Shifts toward poles and higher altitudes in the ranges of plant and animal species. (WGII SfP, page 8)
Projections for North America
For North America, the authors expressed "very high confidence" in these projections:
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Cities that already have heat waves will experience "an increased number, intensity and duration" of such events, "with potential for adverse health impacts." (WGII SfP, page 15)
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Pest, disease and fire disturbances will have "increasing impacts on forests, with an extended period of high fire risk and large increases in area burned." (WGII SfP, page 14)
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Coastal areas "will be increasingly stressed by climate change impacts interacting with development and pollution." (WGII SfP, page 15)
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Growing coastal population and development will "Increase vulnerability to climate variability and future climate change, with losses projected to increase if the intensity of tropical storms increases." (WGII SfP, page 15)
Projections for Other Regions
These were among the working group's regional projections:
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Polar regions ("high confidence") — Reduced "thickness and extent of glaciers and ice sheets, and changes in natural ecosystems with detrimental effects on many organisms including migratory birds, mammals and higher predators." (WGII SfP, page 15)
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Africa ("high confidence") — "Increased water stress due to climate change," affecting 75 million to 250 million people by 2020; "severely compromised" agricultural production, "including access to food" in many countries. (WGII SfP, page 13)
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Asia ("high confidence") — Threats to coastal areas, especially high-population megadeltas, from increased sea flooding, and in some megadeltas, also from river flooding. (WGII SfP, page 13)
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Small islands ("very high confidence") — Special vulnerability "to the effects of climate change, sea-level rise and extreme events." (WGII SfP, page 15)
Mitigation and Adaptation
Statements about measures to reduce ("mitigate") man-made climate change, and measures to adapt to it, included these:
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Combined measures for adaptation and mitigation "can diminish the risks." (WGII SfP, page 20)
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Adaptation is "essential," especially for near-term impacts, because the strictest mitigation measures "cannot avoid further impacts of climate change in the next few decades." (WGII SfP, page 20)
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Without mitigation, long-term effects of climate change would be likely to "exceed the capacity of natural, managed and human systems to adapt." (WGII SfP, page 20)
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