What is the climate sensitivity to a doubling of CO2?

The equilibrium climate sensitivity (ECS) — the global mean surface warming from a sustained doubling of CO2 — is estimated to lie in the range ~2-5°C, but the upper tail is hard to rule out and the lower tail has been narrowed only slowly.

Cloud feedbacks are the dominant source of uncertainty. Resolution matters for projections of future warming and the design of climate policy.