permafrost

The name internationally used for permanently frozen ground. It arises from the fusion of the English words permanent (permanent) and frost (frost, ice). It is the layer of soil - of earth, rock, or a mixture of both, as well as organic matter -, of variable thickness, in which the water it contains is fully or partially frozen throughout the year. Permafrost exists in those cold places on Earth where summer warming fails to fully thaw the ice contained in the soil. Normally, below the surface layer affected by the annual freeze-thaw cycle there is an underlying layer of permanently frozen ground. The rise in temperatures experienced in recent decades at high latitudes of the northern hemisphere (where global warming is manifesting itself most strongly) is causing the seasonal melting of ice in the soil to reach ever greater depths. This circumstance entails the release into the atmosphere of large quantities of methane and CO₂.