Divine, D., Isaksson, E., Martma, T., Meijer, H.A.J., Moore, J., Pohjola, V., van de Wal, R.S.W. and Godtliebsen, F. 2011. Thousand years of winter surface air temperature variations in Svalbard and northern Norway reconstructed from ice-core data. Polar Research 30: 10.3402/polar.v30i0.7379.
Working with ice cores extracted from Svalbard at Lomonosovfonna in 1997 and at Holtedahlfonna in 2005, Divine et al. used the δ18O data derived from them to reconstruct a 1200-year winter (DecJanFeb) surface air temperature history for nearby Longyearbyen (78.25°N, 15.47°E) by calibrating (scaling) the δ18O data to corresponding historically-observed temperatures (since 1911) at that location. And as may be seen from the figure below, the 11-year running-mean peak winter temperature of the Medieval Warm Period was approximately 9°C greater than the end-of-record 11-year running-mean peak winter temperature.
Figure 1. Reconstructed winter surface air temperature (SAT) for Longyearbyen. Adapted from Divine et al. (2011).