Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
doi:10.5194/cp-2017-17
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
21 Feb 2017
Review status
This discussion paper is under review for the journal Climate of the Past (CP).
Atmospheric circulation and hydroclimate impacts of alternative warming scenarios for the Eocene
Henrik Carlson and Rodrigo Caballero Department of Meteorology, Stockholm University
Abstract. Recent work in modelling the warm climates of the Early Eocene shows that it is possible to obtain a reasonable global match between model surface temperature and proxy reconstructions, but only by using extremely high atmospheric CO2 concentrations or more modest CO2 levels complemented by a reduction in global cloud albedo. Understanding the mix of radiative forcing that gave rise to Eocene warmth has important implications for constraining Earth's climate sensitivity, but progress in this direction is hampered by the lack of direct proxy constraints on cloud properties. Here, we explore the potential for distinguishing among different radiative forcing scenarios via their impact on regional climate changes. We do this by comparing climate model simulations of two end-member scenarios: one in which the climate is warmed entirely by CO2, and another in which it is warmed entirely by reduced cloud albedo (which we refer to as the low CO2-thin clouds or LCTC scenario) . The two simulations have almost identical global-mean surface temperature and equator-to-pole temperature difference, but the LCTC scenario has ~ 11 % greater global-mean precipitation. The LCTC simulation also has cooler midlatitude continents and warmer oceans than the high-CO2 scenario, and a tropical climate which is significantly more El Niño-like. We discuss the potential implications of these regional changes for terrestrial hydroclimate and vegetation.

Citation: Carlson, H. and Caballero, R.: Atmospheric circulation and hydroclimate impacts of alternative warming scenarios for the Eocene, Clim. Past Discuss., doi:10.5194/cp-2017-17, in review, 2017.
Henrik Carlson and Rodrigo Caballero
Henrik Carlson and Rodrigo Caballero
Henrik Carlson and Rodrigo Caballero

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Short summary
Climate models are able to simulate the surface temperature of the Early Eocene as reconstructed from paleoclimatology data, but only by using extremely high CO2 concentrations or clouds that are more transparent to solar radiation. We explore the potential for distinguishing among these two forcing agents via their impact on regional climate. Better constraining the radiative forcing that led to Eocene warmth has important implications for understanding Earth’s climate sensitivity.
Climate models are able to simulate the surface temperature of the Early Eocene as reconstructed...
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