What a show Hollywood could make of global warming, if only the West Antarctic Ice Sheet (which is roughly the size of Mexico) would disintegrate all at once, provoking an overnight rise in sea levels of perhaps 15 to 20 feet. Such an event would be catastrophic for many millions of people around the world who live in large coastal urban areas, from New York City to Shanghai. The rising oceans would inundate intensely farmed river deltas, such as the Nile and Ganges. In the real world, however, the melting of the West Antarctic Ice Sheet may take several centuries to unfold, and thus will not reach its climatic end until long after the last members of any present day audience will have left the theater. Ice turns to water one prosaic drop at a time.
Even though the melting of the world’s ice usually lacks Hollywood-style flair, the eventual result may be climate change on a scale that the Earth has not experienced since the days of the dinosaurs. Human-induced climate change may be ending the cycle of glaciation that has been the norm on Earth since the end of the age of the dinosaurs, about 65 million years ago. Viewed on a timescale of the last 540 million years, however, glacial cycles have been relatively rare events. For three-quarters of the last 540 million years, the Earth’s ice caps have been negligible or non-existent (Huber et al. 2000, xi).
As the twenty-first century opened, ice was melting around the world. The Arctic ice cap was thinning, and scientists were speculating over how many years will pass before a summer during which most of it melts. The Intergovernmental Panel on Climate Change’s models project that between one-third and one-half of existing mountain glacial mass could disappear over the next 100 years. Sometime during the present century, the last glacier may melt in Glacier National Park.
Many lakes and rivers in the Northern Hemisphere usually freeze about a week later and thaw out 10 days sooner than a century and a half ago, according to John J. Magnuson and colleagues. In some areas (such as the harbor of