From the latest NIPCC Report:
In a news & views item published in Nature Geoscience, van Ommen (2013) comments on the prior publications of Abram et al. (2013) and Steig et al. (2013), which, in his words, "add to the evidence that changes currently seen in Antarctica are unusual relative to the past 2000 years." And he says that "taken together, alongside other indicators of change, the message is becoming clearer: Antarctica is very likely to be showing a response to the warming climate of the planet," which he says may "reflect the effects of a combination of natural variability and the early impacts of rising greenhouse gas concentrations."
But are the findings of Abram et al. and Steig et al. truly unusual relative to the past 2000 years? In a word, no. And why? Because several scientific studies of Antarctic temperature reconstructions clearly suggest otherwise, as can readily be verified by perusing the brief one-sentence synopses listed below that pertain to a half-dozen journal articles on this subject.
1. Roberts et al. (2004) conducted a fossil diatom analysis of an 82-cm sediment core that was removed from the deepest part of one of the Windmill Islands of East Antarctica, finding a multi-centennial period of warmth (2000-1700 14C yr BP) that experienced summer temperatures they described as being "much higher than present summer temperatures."
2. Hall et al. (2006) found evidence of elephant seal presence at 14 different locations along Antarctica's Victoria Land Coast between 600 BC and AD1400, which they said is indicative of "warmer-than-present climate conditions."
3. Hall (2007) determined that the Collins Ice Cap margin on Fildes Peninsula (King George Island, South Shetland Islands) "is still more extensive than it was prior to ~650 cal. yr BP," which led her to conclude that the climate prior to that time may have been "as warm as or warmer than present."
4. Hall et al. (2010) examined organic-rich sediments exposed by the recent retreat of the Marr Ice Piedmont on western Anvers Island near Norsel Point, finding peat from the exposed sediments dated between 707 ± 36 and 967 ± 47 cal. yr B.P., which led them to conclude that "ice was at or behind its present position at ca. 700-970 cal. yr B.P.," meaning that temperatures during that period were as warm as or warmer than they are currently.
5. Bertler et al. (2011) studied deuterium (δD) data obtained from a 180-meter-long ice core that had been extracted from the ice divide of Victoria Lower Glacier in the northernmost McMurdo Dry Valleys, finding that "the McMurdo Dry Valleys were 0.35°C warmer during the Medieval Warm Period than during the Modern Era."
6. Lu et al. (2012), working with "a downcore δ18O record of natural ikaite hydration waters and crystals collected from the Antarctic Peninsula," found that the "most recent crystals suggest a warming relative to the Little Ice Age in the last century, possibly as part of the regional recent rapid warming," but they add that this latter event "is not yet as extreme in nature as the Medieval Warm Period."
So, no. There is nothing unusual, unnatural or unprecedented about the current level of warmth in and around Antarctica relative to the past 2000 years. And, therefore, there is no logical basis for accusing the historical increase in the air's CO2 concentration over the past 2000 years of having caused any unusual, unnatural or unprecedented warming of the globe, simply because there has been no such warming.
Abram, N., Mulvaney, R., Wolff, E.W., Triest, J., Kipfstuhl, S., Trusel, L.D., Vimeux, F., Fleet, L. and Arrowsmith, C. 2013. Acceleration of snow melt in an Antarctic Peninsula ice core during the twentieth century. Nature Geoscience 6: 404-411.
Bertler, N.A.N., Mayewski, P.A. and Carter, L. 2011. Cold conditions in Antarctica during the Little Ice Age - Implications for abrupt climate change mechanisms. Earth and Planetary Science Letters 308: 41-51.
Hall, B.L. 2007. Late-Holocene advance of the Collins Ice Cap, King George Island, South Shetland Islands. The Holocene 17: 1253-1258.
Hall, B.L., Hoelzel, A.R., Baroni, C., Denton, G.H., Le Boeuf, B.J., Overturf, B. and Topf, A.L. 2006. Holocene elephant seal distribution implies warmer-than-present climate in the Ross Sea. Proceedings of the National Academy of Sciences USA 103: 10,213-10,217.
Hall, B.L., Koffman, T. and Denton, G.H. 2010. Reduced ice extent on the western Antarctic Peninsula at 700-970 cal. yr B.P. Geology 38: 635-638.
Lu, Z., Rickaby, R.E.M., Kennedy, H., Kennedy, P., Pancost, R.D., Shaw, S., Lennie, A., Wellner, J. and Anderson, J.B. 2012. An ikaite record of late Holocene climate at the Antarctic Peninsula. Earth and Planetary Science Letters 325-326: 108-115.
Roberts, D., McMinn, A., Cremer, H., Gore, D.B. and Melles, M. 2004. The Holocene evolution and palaeosalinity history of Beall Lake, Windmill Islands (East Antarctica) using an expanded diatom-based weighted averaging model. Palaeogeography, Palaeoclimatology, Palaeoecology 208: 121-140.
Steig, E.J., Ding, Q., White, J.C.W., Kuettel, M., Rupper, S.B., Neumann, T.A., Neff, P.D., Gallant, A.J.E., Mayewski, P.A., Taylor, K.C., Hoffmann, G., Dixon, D.A., Schoenemann, S., Markle, B.M., Schneider, D.P., Fudge, T.J., Schauer, A.J., Teel, R.P., Vaughn, B., Burgener, L., Williams, J. and Korotkikh, E. 2013. Recent climate and ice-sheet changes in West Antarctica compared with the past 2000 years. Nature Geoscience 6: 372-375.