What does permafrost mean?
Permafrost is ground that remains at or below zero degrees Celsius for at least two consecutive years.
How the process forms and its main drivers
The surface active layer thaws in summer and freezes in winter, while ice, sediment and organic matter may lie below. Permafrost is not pure ice.
Evidence, applications and limits
Thaw can cause subsidence, landslides and infrastructure damage. Decomposition can release carbon dioxide and methane, contributing to climate feedback. Local outcomes vary with climate, geology, topography and human influence, so they require long-term measurements.
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