Methodology:

Locations for each observation are provided. Whilst the exact timing of the peak Arctic Last Interglacial warmth (represented by these observations) has not yet been definitively determined, and is reasonable to assume that these measurements are approximately synchronous across the Arctic during the Last Interglacial, it is not clear that the peak warmth occurs at the same time for the whole of the Northern Hemisphere.

For consistency with modelled data presented by Guarino et al 2020 , temperature anomalies computed against present day conditions (i.e. 1961-1990 baseline) were corrected to take into account a 0.4 K of global warming between preindustrial (1850) and present day (1961-1990) conditions, thus the quoted values values differ slightly (+0.4 K) from the original datasets so that they represent temperature anomalies relative to the preindustrial era.

This is dataset is a compilation. Please refer to original paper for data lineage and methodology.

CAPE Last Interglacial Project Members. Last Interglacial Arctic warmth confirms polar amplification of climate change, Quaternary Science Reviews, Volume 25, Issues 13-14, 2006, Pages 1383-1400, ISSN 0277-3791, https://doi.org/10.1016/j.quascirev.2006.01.033.

IPCC. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. [Stocker, T.F. and Qin, D and Plattner, G and Tignor, M and Allen, S.K. and Boschung, J and Nauels, A and Xia, Y and Bex, V and Midgley, P.M (eds.)]. Tech. Rep. 5, Intergovernmental Panel on Climate Change, Cambridge, United Kingdom and New York, NY, USA (2013).

Kaspar, F., Kuhl, N., Cubasch, U., and Litt, T. (2005), A model-data comparison of European temperatures in the Eemian interglacial, Geophys. Res. Lett., 32, L11703, doi:10.1029/2005GL022456.

Data quality:

Most of the site temperatures are presented with one standard deviation estimates of uncertainty. However for 9 sites, the standard deviation of the temperature data was not available, a standard deviation of +-0.5 K was used to account for this missing uncertainty: this is the smallest standard deviation found in any proxy record across all sites, and is thus as a conservative estimation of the uncertainty associated to proxy data. See Guarino et al 2020 for further information.