A Modeling Perspective on the Lingering Glacial Sea Surface Temperature Conundrum

The strong cooling during the Last Glacial Maximum (LGM, 21 ka BP) provides a rigorous test of climate models' ability to simulate past and future climate changes. We force an atmospheric general circulation model with two recent global LGM sea surface temperature (SST) reconstructions, one suggesting a weak and the other a more pronounced cooling, and compare the simulated land surface temperatures (LSTs) to reconstructed data. Our results do not confirm either SST reconstruction. The cold SST data set leads to good agreement between simulated and observed LSTs at low latitudes, but is systematically too cold at mid‐latitudes. The opposite is true for the warm SST data set. Differences between the simulated LSTs are caused by varying land surface albedos, which is lower for the warmer SST reconstruction. The inconsistency between reconstructed and simulated climate points to a potentially significant bias in the proxy reconstructions and/or the climate sensitivity of current climate models. Plain Language Summary The global temperatures during the Last Glacial Maximum at around 21 ka BP were much lower than at present, mainly caused by large ice sheets covering large parts of North America and Europe as well as a strong reduction in atmospheric greenhouse gas concentration. A quantification of the land and sea surface cooling is necessary to understand the response of the climate system to such forcing, providing a constraint of models for future climate changes. However, recent sea surface temperature (SST) data sets still show discrepancies in the suggested cooling due to different reconstruction methods. We use both a comparably warm and a rather cold SST data set for our model simulations and compare the results to recent land surface temperature (LST) reconstructions in order to assess which SST data set leads to a higher accordance. The results are ambiguous. The warmer SST data set results in too warm simulated LST at low latitudes, but a good accordance at mid‐latitudes. On the other hand, the colder SST data set yields a good accordance for low latitudes, but simulates too cold LST at mid‐latitudes. This model‐data inconsistency demands a critical reexamination of both proxy data and models. Key Points Last Glacial Maximum (LGM) experiments indicate that both warmer and colder sea surface temperature (SSTs) are inconsistent with glacial land surface temperature (LST) reconstructions A higher reconstruction data coverage is needed for low‐elevatio