PNNL

Abstract

Estimates on 21st century global mean surface temperature increase have generally been based on scenarios that do not include climate policies. Newly developed multi-gas mitigation scenarios now allow the assessment of possible impacts of climate policies on projected warming ranges. By combing emission pathway results from multiple energy-economic models, we show that these mitigation scenarios result in a range of 21st century temperature increase of 0.5 to 4.2°C over 1990 levels as compared to 1.3-7.3 °C for the no-policy cases. About half the range is due to differences in the assumed stringency of the global climate policy and half is due to uncertainty in our understanding of the climate system, specifically, the carbon cycle and climate sensitivity. A minimum warming of about 0.5-2.7°C (avg. 1.3oC) remains for even the most stringent stabilization scenarios analyzed here - highlighting the need for both emission mitigation and adaptation policies.