Climate feedback loops are processes by which an initial change in the climate system produces effects that either amplify (positive feedback) or dampen (negative feedback) the original change. Positive feedbacks are the primary mechanism by which moderate initial warming could produce catastrophic outcomes — they are why the relationship between emissions and consequences is nonlinear.
Major positive feedbacks include: ice-albedo feedback (warming melts ice, which is reflective; the exposed dark ocean or land absorbs more heat, producing more warming and more melting); water vapor feedback (warmer air holds more water vapor, which is itself a greenhouse gas, amplifying the initial warming); permafrost carbon feedback (warming thaws permafrost containing vast quantities of organic carbon, which decomposes and releases CO₂ and methane, producing more warming); and forest dieback feedback (drought and heat stress kill forests, which release stored carbon and can no longer absorb CO₂, converting carbon sinks into carbon sources).
These feedbacks interact. Permafrost thaw releases methane, which intensifies warming, which accelerates ice loss, which changes albedo, which intensifies warming further. The concern is that beyond certain tipping points, these feedbacks become self-sustaining — continuing even if human emissions were to stop entirely. This is the mechanism behind the most severe climate projections and the basis for arguments that the window for meaningful mitigation may already be closing.