Permafrost

Permafrost, perennially frozen ground that maintains a temperature at or below the freezing point for at least two years. Vast tracts of permafrost lie across Alaska, Canada, northern Europe and Asia, and Antarctica. About 80 percent of Alaska’s land area contains permafrost. Greenland is almost totally covered with permafrost. Pockets of permafrost are found as far south as the 50th parallel in Canada and the 45th parallel in Siberia. Permafrost can extend to depths of more than 500 m (1,600 ft). Clues to the age of the permafrost of the Northern Hemisphere lie in the numerous discoveries of mammoth remains embedded in frozen ground. Mammoths became extinct about 10,000 to 15,000 years ago, coincident with the end of the most recent ice age. Some scientists, however, think that much of today’s permafrost may have formed as long as 120,000 years ago.

Permafrost contains vast amounts of organic matter. Some scientists estimate that the world’s permafrost may store as much as 450 billion metric tons of carbon. Because it contains so much carbon, scientists are concerned that melting permafrost could contribute to global warming and climate change. When permafrost melts, the carbon contained within it oxidizes and becomes carbon dioxide, a greenhouse gas that absorbs heat radiated from Earth’s surface, trapping heat in the lower atmosphere. Permafrost melting may also release methane, a greenhouse gas that absorbs 20 times as much heat radiation as carbon dioxide.

In August 2005 two scientists reported that permafrost in a vast area in western Siberia was beginning to melt. The area was identified as the world’s largest frozen peat bog, totaling about 1 million sq km (about 386,000 sq mi), or about the size of France and Germany combined. Scientists estimated that the area could store as much as 70 billion metric tons of methane, representing nearly 25 percent of all the methane stored in the world’s land surface. Scientists were especially concerned about the possible implications of permafrost melting because existing computer models that warn of climate change and global warming do not take into account the melting of permafrost. As a result temperature increases predicted by those models could be too low. Scientists are also fearful that melting permafrost could represent a tipping point—that is, a natural change capable of accelerating global warming regardless of cutbacks in industrial or human-made greenhouse gas emissions.