Permafrost is a major presence in northern landscapes and is also found in high mountain regions and ice-free parts of Antarctica. Deep permafrost formations probably represent the oldest ice on the planet. Where present, permafrost alters the water table, shapes the regional geomorphology, and creates significant challenges for infrastructure. Some of the highest rates of coastal erosion in the world are found in ice-rich sediments on the Arctic coast, where sea level rise and diminished sea ice are exposing the coast to increased ocean swell. Other aspects of permafrost interaction in the climate system include its potentially significant role in the global carbon cycle through long-term storage of organic carbon, which, if melted, decomposes to release methane and CO2 to the atmosphere. I discuss this further in chapter 8.

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