Climate model simulation reveals non-linear climate sensitivity under abrupt carbon dioxide forcing, indicating strong mediation by cloud and albedo feedbacks.
Effective climate sensitivity (E ff CS) is a key metric for quantifying climate change, yet its uncertainty remains large, primarily due to intermodel differences in cloud feedback. Here, we assess E ff CS and climate feedback to an abrupt doubling (2xCO2) and quadrupling (4xCO2) of CO 2 over 450 years in GFDL CM4.0. Both runs have comparable E ff CS estimates during the first 50 years (2xCO2: 2.99 K; 4xCO2: 3.25 K) with the 4xCO2 E ff CS estimate still slightly stronger for Years 51–150. Extending the analysis to 450 years increases the E ff CS estimate, but more so in 2xCO2 (5.8 K) than in 4xCO2 (4.79 K). In both runs, the E ff CS increases due to a weakening of the net feedback with warming, largely through shortwave cloud feedback increase. A weaker E ff CS during the slow response for 4xCO2 relative to 2xCO2 is associated with a weaker surface albedo feedback due to an earlier sea‐ice loss in both hemispheres.
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Shrestha et al. (2026) studied this question.
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