Example
Thaw can expose previously frozen organic matter to decomposition.
The catch
The resulting emissions depend on local conditions and timescales.
Related terms
Afforestation, Biodiversity, Blue carbon, Carbon sink, Carbon stock, Deforestation
In more depth
Permafrost, explained.
Permafrost thaw is a climate feedback that people cannot switch off directly, because the only lever is the warming that drives it. Frozen soils across the Arctic and high mountains store more carbon than the atmosphere currently holds. As they thaw, microbes release CO₂ where the ground drains and methane where it stays waterlogged.
IPCC AR6 expects the release to build over decades and centuries, a factor the carbon budget estimates must allow for. The same assessment rates it very unlikely that methane hydrates locked in deep permafrost and under the seabed will cause a sudden, detectable surge this century. The local effects are already visible, as thaw collapses ground into lakes and sinkholes and buckles the roads, pipelines and buildings above it. Treat permafrost emissions as a reason to cut emissions sooner, since each increment of warming thaws more ground.