Last interglacial temperature evolution – a model inter-comparison

Abstract

Abstract. There is a growing number of proxy-based reconstructions detailing the climatic changes that occurred during the last interglacial period (LIG). This period is of special interest, because large parts of the globe were characterized by a warmer-than-present-day climate, making this period an interesting test bed for climate models in light of projected global warming. However, mainly because synchronizing the different palaeoclimatic records is difficult, there is no consensus on a global picture of LIG temperature changes. Here we present the first model inter-comparison of transient simulations covering the LIG period. By comparing the different simulations, we aim at investigating the common signal in the LIG temperature evolution, investigating the main driving forces behind it and at listing the climate feedbacks which cause the most apparent inter-model differences. The model inter-comparison shows a robust Northern Hemisphere July temperature evolution characterized by a maximum between 130–125 ka BP with temperatures 0.3 to 5.3 K above present day. A Southern Hemisphere July temperature maximum, −1.3 to 2.5 K at around 128 ka BP, is only found when changes in the greenhouse gas concentrations are included. The robustness of simulated January temperatures is large in the Southern Hemisphere and the mid-latitudes of the Northern Hemisphere. For these regions maximum January temperature anomalies of respectively −1 to 1.2 K and −0.8 to 2.1 K are simulated for the period after 121 ka BP. In both hemispheres these temperature maxima are in line with the maximum in local summer insolation. In a number of specific regions, a common temperature evolution is not found amongst the models. We show that this is related to feedbacks within the climate system which largely determine the simulated LIG temperature evolution in these regions. Firstly, in the Arctic region, changes in the summer sea-ice cover control the evolution of LIG winter temperatures. Secondly, for the Atlantic region, the Southern Ocean and the North Pacific, possible changes in the characteristics of the Atlantic meridional overturning circulation are crucial. Thirdly, the presence of remnant continental ice from the preceding glacial has shown to be important when determining the timing of maximum LIG warmth in the Northern Hemisphere. Finally, the results reveal that changes in the monsoon regime exert a strong control on the evolution of LIG temperatures over parts of Africa and India. By listing these inter-model differences, we provide a starting point for future proxy-data studies and the sensitivity experiments needed to constrain the climate simulations and to further enhance our understanding of the temperature evolution of the LIG period.

Impact of meltwater on high-latitude early Last Interglacial climate

“…Although previous modelling studies (e.g. Bakker et al, 2013;Holden et al, 2010;Loutre et al, 2014;Sanchez-Goni et al, 2012) have looked at the impact of freshwater forcing on early LIG climate, they did not link the response with the data reconstructions in the highlatitude regions of the Northern and Southern Hemispheres and did not attribute this to a bipolar seesaw mechanism. As such, we perform the first rigorous model-data comparison approach to examine the impact and sensitivity of freshwater forcing on the high-latitude climate of the early LIG to test whether the hypothesis of a bipolar mechanism is feasible in the framework of a comprehensive fully coupled climate model to explain the difference in peak warmth conditions between hemispheres at 130 ka.…”

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

“…The dataset consists of several time slices; including 125 ka employed here. While being based on a smaller number of records, it benefits from having a coherent temporal (Govin et al 2012;Bakker et al 2013), and as highlighted by Bakker and Renssen (2014) the 'synchronous warming' assumption behind the previous data compilations contributes to model-data mismatch. Thus, we have preferred the Capron et al (2014) dataset for model-data comparison due to the consistent dating; despite the more limited spatial coverage.…”

“…We focus on 125 ka, when high northern latitude temperatures are near peak LIG warming (NEEM community members 2013; Bakker et al 2013) and the sea level stabilizing (Masson-Delmotte et al 2013;Kopp et al 2013) indicating that ice sheet retreat and related freshwater flux into the ocean is diminishing. In line with the PMIP3 125 ka experiment, the simulation is only forced by insolation changes and changes in the atmospheric gas composition, while the ice sheets and vegetation are kept unchanged.…”

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

“…AOGCMs though have not been able to produce the warming indicated by the East Antarctic ice cores when forced by orbital forcing changes only [17,18]. Transient simulations for the LIG with intermediate complexity models [19] suggest that Arctic warming peaked early in the interglaciation because obliquity peaked earlier than precession [20], while meltwater forcing introduced to the North Atlantic can generate an early Antarctic warming [17].…”