What Is Permafrost?

Permafrost underlies vast areas of Siberia, northern Canada, Alaska, Greenland, and the Tibetan Plateau — about 23 million square kilometres. It can extend hundreds of metres deep; the deepest known permafrost in Siberia reaches about 1,500 metres. An "active layer" above the permafrost thaws each summer (typically 0.3-2 metres) and refreezes in winter. Permafrost contains an estimated 1,500 gigatonnes of organic carbon — nearly twice the amount currently in the atmosphere as CO2. As global temperatures rise, permafrost is thawing at accelerating rates, releasing methane and CO2, creating a dangerous positive feedback loop. Thawing permafrost also destabilises infrastructure: buildings, roads, and pipelines in Arctic regions are subsiding and cracking as their frozen foundations soften. Ancient viruses, bacteria, and even intact woolly mammoth specimens have been found preserved in permafrost.