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Observational Constraints on the Effective Climate Sensitivity from the Historical PeriodThe observed warming in the atmosphere and ocean can be used to estimate the climate sensitivity linked to present-day feedbacks, which is referred to as the effective climate sensitivity (Shist). However, such an estimate is affected by uncertainty in the radiative forcing, particularly aerosols, over the historical period. Here, we make use of detection and attribution techniques to derive the surface air temperature and ocean warming that can be attributed directly to greenhouse gas increases. These serve as inputs to a simple energy budget to infer the likelihood of Shist in response to observed greenhouse gases increases over two time periods (1862–2012 and 1955–2012). The benefit of using greenhouse gas attributable quantities is that they are not subject to uncertainties in the aerosol forcing (other than uncertainty in the attribution to greenhouse gas versus aerosol forcing not captured by the multi-model aerosol response pattern). The resulting effective climate sensitivity estimate, Shist, ranges from 1.3 °Cto 3.1 °C(5%–95% range) over the full instrumental period (1862–2012) for our best estimate, and gets slightly wider when considering further uncertainties. This estimate increases to 1.7 °C–4.6 °C if using the shorter period (1955–2012).We also evaluate the climate model simulated surface air temperature and ocean heat content increase in response to greenhouse gas forcing over the same periods, and compare them with the observationally-constrained values.We find that that the ocean warming simulated in greenhouse gas only simulations in models considered here is consistent with that attributed to greenhouse gas increases from observations, while one model simulates more greenhouse gas-induced surface air warming than observed. However, other models with sensitivity outside our range show greenhouse gas warming that is consistent with that attributed in observations, emphasising that feedbacks during the historical period may differ from the feedbacks at CO2 doubling and from those at true equilibrium.
Document ID
20200002154
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Tokarska, Katarzyna B
(University of Edinburgh Edinburgh, Scotland, United Kingdom)
Hegerl, Gabriele C.
(University of Edinburgh Edinburgh, Scotland, United Kingdom)
Schurer, Andrew P.
(University of Edinburgh Edinburgh, Scotland, United Kingdom)
Forster, Piers M.
(University of Leeds Leeds, United Kingdom)
Marvel, Kate
(Columbia University New York, NY, United States)
Date Acquired
April 2, 2020
Publication Date
March 5, 2020
Publication Information
Publication: Environmental Research Letters
Publisher: IOP Science
Volume: 15
Issue: 3
e-ISSN: 1748-9326
Subject Category
Meteorology And Climatology
Report/Patent Number
GSFC-E-DAA-TN78972
Funding Number(s)
CONTRACT_GRANT: 80NSSC17M0057
Distribution Limits
Public
Copyright
Use by or on behalf of the US Gov. Permitted.
Technical Review
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