Constraining Transient Climate Response Using the Historical Temperature Record

Abstract

Anthropogenic greenhouse gas emissions alter the planet's energy balance and cause heating of the surface and oceans. Estimates of the implications of continued emissions are necessary to assess the severity of the situation. The transient climate response (TCR) is a measure of the climate's response to a continued increase in CO2 concentration, and indicates how much the temperature will increase in the coming decades if emission continues. However, uncertainty in estimates are still large and projections of TCR vary significantly between climate models in the Coupled Model Intercomparison Project (CMIP5) ensemble.

A new method to constrain the likely range of TCR is developed on the basis of a simple energy balance model (EBM). From recent estimates of historical radiative forcing and the global instrumental temperature record, a probability density function (pdf) for TCR is calculated. A 5-95 % confidence interval is found, that suggests that models with the highest TCR values are inconsistent with the observed temperature record.