Permafrost
Ground that remains frozen year-round, containing large carbon stores vulnerable to thawing with climate warming.
Real World
In Yakutsk, Siberia — the world's coldest city — buildings are sinking and cracking as permafrost thaw destabilises foundations, forcing Russia to spend billions on infrastructure repairs.
Exam Focus
Link permafrost thaw to positive feedback explicitly — state that released methane causes further warming, which causes further thaw.
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