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.
In introducing the purpose for their study, the authors write that "the recent rapid climate and environmental changes in the Arctic, for instance, sea-ice retreat (e.g., Comiso et al., 2008) and ice-sheet melting (e.g., van den Broeke et al., 2009), require a focus on long-term variability in this area in order to view these recent changes in the long-term context," which is truly essential if one desires to know just how unusual, unnatural or unprecedented the recent warming of the Arctic has been.
What was done
Working with ice cores extracted from Svalbard at Lomonosovfonna in 1997 (Isaksson et al., 2001) and at Holtedahlfonna in 2005 (Sjorgren et al., 2007), Divine et al. used the δ18O data derived from them to reconstruct 1200-year winter (DecJanFeb) surface air temperature histories for nearby Longyearbyen (78.25°N, 15.47°E) and farther-afield Vardo (70.54°N, 30.61°E, in northern Norway), by calibrating (scaling) the δ18O data to corresponding historically-observed temperatures at the two locations, which for Longyearbyen were first collected in 1911 and for Vardo have been extended back to 1840 as a result of the work of Polyakov et al. (2003).
What was learned
The winter surface air temperature reconstructions, which are depicted in the figure below, begin at the peak warmth of the Medieval Warm Period at approximately AD 800, and they decline fairly steadily to the coldest period of the Little Ice Age at approximately AD 1830, after which they rise into the 1930s, decline, and then rise again, to terminate just slightly lower than their 1930s' peaks near the end of the 1990s.
As may readily be determined from Divine et al.'s results, 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 at Longyearbyen, while it was about 3.3°C warmer at Vardo.
What it means
Not only is there nothing unusual, unnatural or unprecedented about the most recent surface air temperatures at Longyearbyen and Vardo, it is pretty clear that it was significantly warmer at both locations during the peak warmth of the Medieval Warm Period, when there was way less CO2 in the atmosphere than there is today. And this observation suggests - as do many others from all around the world (see our Medieval Warm Period Project) - that anthropogenic CO2 emissions are not the great threat to humanity and the biosphere that climate alarmists claim them to be, for something in the environment appears to be effectively counteracting whatever "greenhouse effect" they may produce.
Comiso, J.C., Parkinson, C.L., Gersten, R. and Stock, L. 2008. Accelerated decline in the Arctic sea ice cover. Geophysical Research Letters 35: 10.1029/2007GL031972.
Isaksson, E., Pohjola, V., Jauhiainen, T., Moore, J., Pinglot, J.-F., Vaikmae, R., van de Wal, R.S.W., Hagen, J.-O., Ivask, J., Karlof, L. , Martma, T., Meijer, H.A.J., Mulvaney, R., Thomassen, M.P.A. and van den Broeke, M. 2001. A new ice core record from Lomonosovfonna, Svalbard: viewing the data between 1920-1997 in relation to present climate and environmental conditions. Journal of Glaciology 47: 335-345.
Sjogren, B., Brandt, O., Nuth, C., Isaksson, E., Pohjola, V.A., Kohler, J. and van de Wal, R.S.W. 2007. Determination of firn density in ice cores using image analysis. Journal of Glaciology 53: 413-419.
van den Broeke, M., Bamber, J., Ettema, J., Rignot, E., Schrama, E., van de Berg, W.J., van Meijgaard, E., Velicogna, I. and Wouters, B. 2009. Partitioning recent Greenland mass loss. Science 326: 984-986.Reviewed 1 August 2012