Abstract

Will the climate become more sensitive to greenhouse gas forcing as it becomes warmer? Several climate model experiments with instantaneous quadrupling of the atmospheric CO2 content point in that direction.

In such experiments, effective climate sensitivity is obtained by extrapolating the global surface temperature response to a new climate equilibrium having zero radiative imbalance at the top of the atmosphere. Many models show that the projection of climate sensitivity increase considerably after about 20 years. The reasons behind are discussed -- and as often is the case -- the Arctic appears to play a role.