Recent advances on the dynamical representation and our understanding of the warmer-than-present last interglacial climate

The Last Interglacial (LIG, ~129-116 thousand years Before Present, hereafter ka) represents an ideal case study to understand the climate mechanisms at play under a warmer-than-present climate. However a spatio-temporal representation of the LIG climatic changes remains difficult to obtain, mainly because aligning paleoclimatic records from various archives (i.e. polar ice cores, marine sediments, speleothems) from around the globe is challenging. Here we summarize recent studies that highlight how the coupling of a synthesis of surface air and sea temperature records (above polar ice sheets and from the North Atlantic and Southern Ocean respectively) associated with harmonized chronologies and of appropriate climate model experiments improved our spatio-temporal representation of the LIG high-latitude climate evolution, and our understanding of the mechanisms at play, especially at the beginning of the LIG. In particular, we describe commonly-used record alignment strategies for marine sediment cores and we show that age discrepancies larger than 4 ka can exist between the timescales inferred from the different approaches. Providing harmonized chronologies when comparing multiple records is thus essential and we propose a new high latitude LIG data synthesis based on coherent record time scales together with associated time slices at 130, 125, 120 and 115 ka of surface temperature anomalies relative to present-day. The results provide the first robust evidence for asynchronous surface temperature evolutions at the LIG onset across the world and also enable one to identify important missing processes in state-of-the-art model climate simulations to reproduce the early LIG climate evolution. Our integrated model-data approach shows that a freshwater input into the North Atlantic (due to the Northern Hemisphere ice sheet early melting) needs to be accounted for in addition to the orbital and greenhouse gas concentration forcing in climate simulations, to explain the evolution of the early LIG climate.

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