The last interglacial (Eemian) climate simulated by LOVECLIM and CCSM3

Abstract

This paper presents a detailed analysis of the climate of the last interglacial simulated by two climate models of different complexities, CCSM3 (Community Climate System Model 3) and LOVECLIM (LOch-Vecode-Ecbilt-CLio-agIsm Model). The simulated surface temperature, hydrological cycle, vegetation and ENSO variability during the last interglacial are analyzed through the comparison with the simulated pre-industrial (PI) climate. In both models, the last interglacial period is characterized by a significant warming (cooling) over almost all the continents during boreal summer (winter) leading to a largely increased (reduced) seasonal contrast in the Northern (Southern) Hemisphere. This is mainly due to the much higher (lower) insolation received by the whole Earth in boreal summer (winter) during this interglacial. The Arctic is warmer than PI through the whole year, resulting from its much higher summer insolation, its remnant effect in the following fall-winter through the interactions between atmosphere, ocean and sea ice and feedbacks from sea ice and snow cover. Discrepancies exist in the sea-ice formation zones between the two models. Cooling is simulated by CCSM3 in the Greenland and Norwegian seas and near the shelves of Antarctica during DJF but not in LOVECLIM as a result of excessive sea-ice formation. Intensified African monsoon is responsible for the cooling during summer in northern Africa and on the Arabian Peninsula. Over India, the precipitation maximum is found further west, while in Africa the precipitation maximum migrates further north. Trees and grassland expand north in Sahel/Sahara, more clearly seen in LOVECLIM than in CCSM3 results. A mix of forest and grassland occupies continents and expands deep into the high northern latitudes. Desert areas reduce significantly in the Northern Hemisphere, but increase in northern Australia. The interannual SST variability of the tropical Pacific (El-Niño Southern Oscillation) of the last interglacial simulated by CCSM3 shows slightly larger variability and magnitude compared to the PI. However, the SST variability in our LOVECLIM simulations is particularly small due to the overestimated thermocline's depth

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

“…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).…”

“…Proxy records from the Arctic region indicate a general northward shift in the vegetation types: The Arctic and sub-Arctic tundra was replaced by boreal and deciduous forest which regionally extended to the coast of the Arctic Ocean (Lozhkin and Anderson 1995;Edwards et al 2003). Climate-vegetation models of varying complexity find the same tendency (Harrison et al 1995;Schurgers et al 2007;Nikolova et al 2013), along with an increased Arctic warming related to the expanded vegetation (Crucifix and Loutre 2002;Schurgers et al 2007). The increased warming can be explained by the albedo impact of the changed vegetation.…”

“…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).…”

“…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).…”

Views on grand research challenges for Quaternary geology, geomorphology and environments

“…New knowledge is needed globally on the state of glaciers, ice sheets, northern tree line, tropics, and subtropics and arid lands during past interglacial periods such as the Eemian, ca. 130 ka ago (Dahl-Jensen et al, 2013;Nikolova et al, 2013) and during a shorter warm period centered around 80 ka, when sea level appears to be near current levels (Dorale et al, 2010). Additional insights are critical for the non-analogous climate response of Southern Hemisphere glaciers, lakes, rivers, and eolian systems, particularly in areas influenced by monsoonal variability, which was potentially intensified by ice sheet-induced cooling of the Northern Hemisphere oceans (Kanner et al, 2012;Rhodes et al, 2015).…”