…We propose three possible reasons why our study yields lower estimates of ECS2xC than previous work that also used LGM data. Firstly, the new reconstructions of LGM surface temperatures show less cooling than previous studies
…Tropical Atlantic SSTs between 20°S–20°N are estimated to be only 2.4 K colder during the LGM in the new reconstruction compared to 3 K used in (23), explaining most of the difference between their higher estimates of ECS2xC and TLGM (–5.9 K vs –3.5 K)
…The second reason is limited spatial data coverage
…Averaging over all grid points in our model leads to a higher global mean temperature (SST over ocean, SAT over land) change (–2.6 K) than using only grid points where paleo data are available (–2.2 K), suggesting that the existing dataset is still spatially biased towards low latitudes and/or oceans. Increased spatial coverage of climate reconstructions is therefore necessary in order to improve ECS2xC estimates.
…A third reason may be the neglect of dust radiative forcing in some previous LGM studies
…Our uncertainty analysis is not complete and does not explicitly consider uncertainties in radiative forcing due to ice sheet extent or different vegetation distributions. Our limited model ensemble does not scan the full parameter range, neglecting, for example, possible variations in shortwave radiation due to clouds. Non-linear cloud feedbacks in different complex models make the relation between LGM and 2CO2 derived climate sensitivity more ambiguous than apparent in our simplified model ensemble (27). More work, in which these and other uncertainties are considered, will be required for a more complete assessment…