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MISU seminar | Diego Jiménez-de-la-Cuesta

Emergent constraints on Earth's transient- and equilibrium response to doubled CO2 by post-1970s global warming

by Diego Jiménez-de-la-Cuesta
Max Planck Institute for Meteorology, Germany


Time: 11 December 2018, 11h15–12h15
Venue: Rossbysalen C609, Arrhenius Laboratory, 6th floor

Abstract
Future global surface warming is determined by both greenhouse gas emission pathways and Earth's transient- (TCR) and equilibrium (ECS) climate response to doubled atmospheric CO2. Energy-balance inference from the instrumental record typically yield best estimates of TCR around 1.3 K and ECS of 1.5–2.0 K: both of which are at the lower end of that in contemporary climate models. Uncertainty in such inference arises primarily from the poorly known aerosol-induced cooling since early industrialisation.

Further, ECS may be underestimated due to temporary cooling induced by evolving sea surface temperature (SST) patterns. Here we present an emergent constraint based on post-1970s warming derived from a multi-model ensemble, taking advantage of the period's weakly-varying aerosol cooling, to obtain a TCR of 1.67 K (1.17–2.16, 5th-95th percentile) and an ECS of 2.83 K (1.72–4.12). A 20 percent increase in TCR relative to energy-balance inference is explained by the neglect of upper-ocean energy storage in past studies, and further, out-of-range TCR would require steep changes in post-1970s aerosol cooling which now appear implausible. High-end ECS values could be supported if SST pattern-effects are larger than that in climate models, a possibility for which there is some recent evidence, thereby in turn making low-end ECS even less likely.

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