This dataset comprises summary statistics regarding historical and projected Southern Hemisphere total sea ice area (SIA) and 21st century global temperature change (dTAS), evaluated from the multi-model ensembles contributing to CMIP5 and CMIP6 (Coupled Model Intercomparison Project phases 5 and 6). The metrics are evaluated for two climatological periods (1979-2014 and 2081-2100) from a number of CMIP experiments; historical, and ScenarioMIP or RCP runs. These metrics were calculated to calculate projections of future Antarctic sea ice loss, and drivers of ensemble spread in this variable, for Holmes et al. (2022) "Antarctic sea ice projections constrained by historical ice cover and future global temperature change". Funding was provided by the British Antarctic Survey Polar Science for Planet Earth Programme and under NERC large grant NE/N01829X/1

The dataset contains chronological and biomarker compound and brGDGT (branched Glyceryl Dialkyl Glyceryl Tetraether) mean summer temperature (MSAT) data for the last c. 6,000 years from sediments extracted from Fan Lake on Annenkov Island (near South Georgia) and Yanou Lake, King George Island, South Shetland Islands. Temperature was reconstructed using the Pearson et al. (2011) global calibration and the Foster et al. (2016) Antarctic calibration. For the latter, we studied 32 lakes from Antarctica, the sub-Antarctic Islands and Southern Chile to: 1) quantify their GDGT composition and investigate the environmental controls on GDGT composition; and 2) develop a GDGT-temperature calibration model for inferring past temperatures from Antarctic and sub-Antarctic lakes. The downcore temperature reconstruction data produced using the new Antarctic brGDGT-temperature calibration were tested on Fan Lake and Yanou Lake to provide a proof of concept for the new calibration model in the Southern Hemisphere. This study is an output of the British Antarctic Survey (BAS) Natural Environment Research Council (NERC) funded Science Program, and was funded by NERC Studentship NE/J500173/1 to LF (BAS and Newcastle University) with additional support from: the European Commission under the 7th Framework Programme through the Action - IMCONet (FP7 IRSES, action No.319718 and the ESF-funded IMCOAST project AP6 to SJR, both coordinated by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Germany). Additional funding from the Natural Environmental Research Council (NERC-CASS), and the German Research Foundation (DFG project no. BR 775/25-1). Logistic support from the NERC-British Antarctic Survey (BAS), HMS Endurance and 892 Naval Air Squadron, the Alfred Wegner Institute (AWI) and the Instituto Antartico Argentino (IAA).