Supplementary Information and Figures from The utility of the historical record for assessing the transient climate response to cumulative emissions

2018-02-12T09:38:09Z (GMT) by Richard J. Millar Pierre Friedlingstein
The historical observational record offers a way to constrain the relationship between cumulative carbon dioxide emissions and global mean warming. We use a standard detection and attribution technique, along with observational uncertainties to estimate the all-forcing or ‘effective’ transient climate response to cumulative emissions (TCREs) from the observational record. Accounting for observational uncertainty and uncertainty in historical non-CO2 radiative forcing gives a best-estimate from the historical record of 1.84°C/TtC (1.43–2.37°C/TtC 5–95‰ uncertainty) for the effective TCRE and 1.31°C/TtC (0.88–2.60°C/TtC 5–95‰ uncertainty) for the CO2-only TCRE. While the best-estimate TCRE lies in the lower half of the IPCC likely range, the high upper bound is associated with the not-ruled-out possibility of a strongly negative aerosol forcing. Earth System Models typically have a higher effective TCRE range when compared like-for-like with the observations over the historical integrations, associated in part with a slight underestimate of diagnosed cumulative emissions relative to the observational best-estimate, a larger ensemble mean-simulated CO2-induced warming and rapid post-2000 non-CO2 warming in some ensemble members.This article is part of the themed issue ‘The Paris Agreement: Understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels'.