Seminar

Abstract

With the development of coupled climate-carbon cycle models new insights into the response of the Earth system to anthropogenic CO2 emissions are emerging. I will present results of climate-carbon cycle experiments with models of intermediate and higher complexity showing that: (1) the global mean temperature response to a pulse of CO2 is approximately constant on timescales of decades to centuries, and declines only slowly thereafter; (2) for a given amount of cumulative CO2 emissions, the stabilization temperature is independent of the timing of those emissions; and (3) the persistent warming from past emissions is proportional to cumulative CO2 emissions. These findings have important implications for climate policy, as they suggest an international framework aimed at avoiding "dangerous anthropogenic interference" based on cumulative CO2 emissions targets. We estimate that in order to stabilize global mean temperature increase at 2C above preindustrial levels with a probability of at least 0.66, cumulative CO2 emissions form 2001 to 2500 must not exceed a median estimate of 590 PgC (range, 200 to 950 PgC). Furthermore, the longevity of the anthropogenic CO2 perturbation challenges the feasibility (without geo-engineering) of pronounced CO2 concentration overshoot scenarios, which have been proposed as a cost-effective strategy for climate stabilization.