Thawing Permafrost

By the 2040's, "for several decades the warming climate in the north will have been thawing the permafrost, the previously frozen soils that exist below the tundra and forests of much of Alaska, Northern Canada and Russia. It is a trend that is much harder to detect or to predict than the retreat of the sea ice, yet it is potentially far more hazardous... Within a few years, the entire north - an area that accounts for a quarter of the land surface in the northern hemisphere - could become a mud bath as the ice that held the soil together disappears. There would be massive landslides and vast floods as millions of cubic meters of newly fluid soils seek lower ground... But the key consequence of the thaw would affect everyone on earth. For thousands of years, the permafrost has locked in an estimated 1,400 gigatonnes of carbon - four times more carbon than humankind has emitted in the last 200 years, and twice as much as there is in the atmosphere. The thaw would release this carbon, gradually, over many years, turning on a gas tap of methane and carbon dioxide that would probably never be able to turn off."

David Attenborough. A Life on Our Planet. 2020. p114-115.