Impact of Global Mean Sea level for LIG and present day climates: an intercomparison of ESMs

The Earth is experiencing an unprecedented fast climate global warming. The global mean seal level (GMSL) rise, resulting from the different SSPs scenarios leads to an increase from 0.5 to 1 m for the end of this century and about 10 m for the 23rd century.

To investigate whether this GMSL rise may act as a climate forcing by itself, an appropriate framework is the last. Indeed, the GMSL was 2 to 6m higher than today, due to a different configuration of the Greeenland and West Antarctica ice sheet. Nevertheless, most simulations of this period (127ka BP)  only account for orbital parameters and greenhouse gases (CO₂, CH₄, and N₂O) changes.

A first publication (Z. Zhang et al. Nat. Geosciences 2023), using the NORESM F1 model, demonstrated that, accounting for this GMSL rise superimposed with the insolation and greenhouse gas forcing factors helps to solve the mismatch pointed out when comparing pmip4 simulations results and SST reconstructions derived from different proxies.  Nevertheless, it was necessary to confirm this important finding with another ESM.

Therefore, we performed, using the same protocol than Zhang et al.  2023, LIG simulations With IPSL CM6 ESM. Both models were involved in PMIP4 LIG intercomparison (Otto-Bliesner  CP 2021) and show good agreement with other ESMs and reasonable agreement with data. A robust feature emerging from this intercomparison was that all models depicted an overestimation of SST for the Southern Hemisphere.

New results within IPSL CM6 demonstrate first that, indeed, GMSL is an important forcing factor for LIG.  In other words, the GMSL rise is not only a consequence of the warming but is also an important driver of this warming.  A second important result is that the spatial pattern of SST response to GMSL is model dependent.  Specifically, the AMOC decrease is enhanced in IPSL model and a difference in bathymetry of Bering strait in both models led to opposite response over Artic Ocean.

Considering the impact of GMSL for LIG depicted by both models, we also did a comparison of GMSL impact for the present interglacial period. We will also present results obtained with IPSL CM6 when using GMSL rise corresponding to 1.25 m that could be reached at the end of this century or 5 to 10m, that could be reached at the end of the 23^rd century.