Global warming under old and new scenarios using IPCC climate sensitivity range estimates

Abstract

Climate projections for the fourth assessment report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) were based on scenarios from the Special Report on Emissions Scenarios (SRES) and simulations of the third phase of the Coupled Model Intercomparison Project (CMIP3). Since then, a new set of four scenarios (the representative concentration pathways or RCPs) was designed. Climate projections in the IPCC fifth assessment report (AR5) will be based on the fifth phase of the Coupled Model Intercomparison Project (CMIP5), which incorporates the latest versions of climate models and focuses on RCPs. This implies that by AR5 both models and scenarios will have changed, making a comparison with earlier literature challenging. To facilitate this comparison, we provide probabilistic climate projections of both SRES scenarios and RCPs in a single consistent framework. These estimates are based on a model set-up that probabilistically takes into account the overall consensus understanding of climate sensitivity uncertainty, synthesizes the understanding of climate system and carbon-cycle behaviour, and is at the same time constrained by the observed historical warming. © 2012 Macmillan Publishers Limited. All rights reserved.