How warm was the last interglacial? New model–data comparisons

Abstract

A Community Climate System Model, Version 3 (CCSM3) simulation for 125 ka during the Last Interglacial (LIG) is compared to two recent proxy reconstructions to evaluate surface temperature changes from modern times. The dominant forcing change from modern, the orbital forcing, modified the incoming solar insolation at the top of the atmosphere, resulting in large positive anomalies in boreal summer. Greenhouse gas concentrations are similar to those of the pre-industrial (PI) Holocene. CCSM3 simulates an enhanced seasonal cycle over the Northern Hemisphere continents with warming most developed during boreal summer. In addition, year-round warming over the North Atlantic is associated with a seasonal memory of sea ice retreat in CCSM3, which extends the effects of positive summer insolation anomalies on the high-latitude oceans to winter months. The simulated Arctic terrestrial annual warming, though, is much less than the observational evidence, suggesting either missing feedbacks in the simulation and/or interpretation of the proxies. Over Antarctica, CCSM3 cannot reproduce the large LIG warming recorded by the Antarctic ice cores, even with simulations designed to consider observed evidence of early LIG warmth in Southern Ocean and Antarctica records and the possible disintegration of the West Antarctic Ice Sheet. Comparisons with a HadCM3 simulation indicate that sea ice is important for understanding model polar responses. Overall, the models simulate little global annual surface temperature change, while the proxy reconstructions suggest a global annual warming at LIG (as compared to the PI Holocene) of approximately 1 ° C, though with possible spatial sampling biases. The CCSM3 SRES B1 (low scenario) future projections suggest high-latitude warmth similar to that reconstructed for the LIG may be exceeded before the end of this century.

The last interglacial climate: comparing direct and indirect impacts of insolation changes

“…While these patterns agree qualitatively with proxy reconstructions, the models generally underestimate the magnitude of the changes Masson-Delmotte et al 2013;Lunt et al 2013;Otto-Bliesner et al 2013). Several models have the strongest warming occurring in the North Atlantic region as a consequence of retreating sea ice and changes in the ocean circulation (Fischer and Jungclaus 2010;Lunt et al 2013;Nikolova et al 2013;Otto-Bliesner et al 2013).…”

“…The latest IPCC report estimates a multi-model annual mean surface warming of 0.0 ± 0.5 K (Masson-Delmotte et al 2013), while Lunt et al (2013) find warming in the Arctic and cooling in the African and Indian monsoon regions as the only robust annual mean results in their intercomparison of 14 models. Seasonally, the models consistently simulate warming over Northern Hemisphere continents during summer (June-July-August; JJA) and global cooling (except in the Arctic) during winter (December-January-February, DJF) (Lunt et al 2013;Nikolova et al 2013;Otto-Bliesner et al 2013;Langebroek and Nisancioglu 2014). While these patterns agree qualitatively with proxy reconstructions, the models generally underestimate the magnitude of the changes Masson-Delmotte et al 2013;Lunt et al 2013;Otto-Bliesner et al 2013).…”

“…Seasonally, the models consistently simulate warming over Northern Hemisphere continents during summer (June-July-August; JJA) and global cooling (except in the Arctic) during winter (December-January-February, DJF) (Lunt et al 2013;Nikolova et al 2013;Otto-Bliesner et al 2013;Langebroek and Nisancioglu 2014). While these patterns agree qualitatively with proxy reconstructions, the models generally underestimate the magnitude of the changes Masson-Delmotte et al 2013;Lunt et al 2013;Otto-Bliesner et al 2013). Several models have the strongest warming occurring in the North Atlantic region as a consequence of retreating sea ice and changes in the ocean circulation (Fischer and Jungclaus 2010;Lunt et al 2013;Nikolova et al 2013;Otto-Bliesner et al 2013).…”

“…Clark and Huybers 2009). The availability of paleoclimate information furthermore means that climate model simulations of the last interglacial are an opportunity to evaluate model performance outside of near-present day conditions, potentially leading to improved projections of future warming (OttoBliesner et al 2006;Braconnot et al 2012;Otto-Bliesner et al 2013). …”

“…Transient simulations usually rely on earth system models of intermediate complexity , while general circulation models (GCMs) primarily are employed for equilibrium, snapshot simulations (Fischer and Jungclaus 2010;Govin et al 2012;Lunt et al 2013;Nikolova et al 2013;Otto-Bliesner et al 2013;Langebroek and Nisancioglu 2014). Recent model assessments find very low global annual mean warming during LIG, contrasting the proxy reconstruction estimate of 1-2 K warming (Masson-Delmotte et al 2013;Otto-Bliesner et al 2013). The latest IPCC report estimates a multi-model annual mean surface warming of 0.0 ± 0.5 K (Masson-Delmotte et al 2013), while Lunt et al (2013) find warming in the Arctic and cooling in the African and Indian monsoon regions as the only robust annual mean results in their intercomparison of 14 models.…”