ABSTRACT
The impacts of climate change are often popularized in terms of photogenic species such as coral and polar bears. The expected effects on natural systems, however, extend well beyond the best-known images. If business-as-usual emissions continue, the most likely late-21st-century temperature increase is more than 4°C (with a one-in-ten chance of exceeding 7°C; see Chapter 1). With 2 to 3°C of warming, AR4 projected that 20 to 30 percent of plant and animal species are likely to be at high risk of extinction and that substantial changes in the structure and functioning of terrestrial and aquatic ecosystems are very likely. With 1.7°C warming, all coral reefs will be bleached, and by 2.5°C they will be extinct; at 2.8°C there is high risk of extinction for polar bears and other Arctic mammals. At 4°C of warming, AR4 projects major extinctions around the world (IPCC 2007a, Working Group II, Chapter 4).
