6.3 Climate Feedbacks
Climate feedbacks amplify or dampen the initial response to forcing. Understanding feedbacks is crucial for predicting climate sensitivity.
Major Feedbacks
Water Vapor (+)
Warmer air holds more H₂O → more greenhouse effect. Strongest positive feedback.
Ice-Albedo (+)
Warming melts ice → lower albedo → more absorption → more warming.
Cloud (uncertain)
Complex: low clouds cool (reflect), high clouds warm (trap IR). Net effect uncertain.
Planck (-)
Warmer Earth radiates more → negative feedback that limits warming.
Climate Sensitivity
$$\Delta T = \frac{\Delta F}{\lambda} = \frac{\Delta F}{\lambda_0(1-f)}$$
ECS (2×CO₂): likely 2.5-4°C (IPCC AR6)