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Philos Trans A Math Phys Eng Sci. 2018 May 13;376(2119). pii: 20160449. doi: 10.1098/rsta.2016.0449.

The utility of the historical record for assessing the transient climate response to cumulative emissions.

Author information

1
College of Engineering, Mathematical and Physical Sciences, University of Exeter, Exeter, UK richard.millar@ouce.ox.ac.uk.
2
Environmental Change Institute, University of Oxford, Oxford, UK.
3
College of Engineering, Mathematical and Physical Sciences, University of Exeter, Exeter, UK.

Abstract

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 (TCRE) 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 have a higher effective TCRE range when compared like-for-like with the observations over the historical period, 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 theme issue 'The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels'.

KEYWORDS:

Paris Agreement; carbon budgets; carbon cycle; climate change

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