Although large changes in climate are a natural part of Earth history, there is little doubt that human activities have caused observed patterns of global warming in the twentieth and twenty-first centuries. Global climate change has large implications for both humans and wildlife. Many threatened and endangered species, which already lead a precarious existence, are likely to suffer further declines. Global warming also threatens populations of species that were once relatively secure, and is likely to result in the endangerment of more species in the future.

A study of habitats comprising 20 percent of the earth's surface suggested that 15 to 37 percent of the world's species may be extinct by 2050 if recent warming trends continue ("Extinction Risk from Climate Change," Nature, no. 427, January 2004.) Summarizing his findings, ecologist Chris D. Thomas said, "The midrange estimate is that 24 percent of plants and animals will be committed to extinction...