Background
The authors write that "over the past 50 years, the Antarctic Peninsula warmed ~2°C," and that resultant rapid breakups "have destroyed several small, thin ice shelves fringing the Antarctic Peninsula (i.e., Cook and Vaughan, 2009, and references therein)." Climate alarmists make much of this phenomenal warming and its destructive impact on the peninsula's ice; but before we get too excited about what's happening there, we have to ask ourselves, as the authors do: "Is the recent warming of the Antarctic Peninsula unique in the Holocene?"

What was done
"In order to put current ice recession in context," as they describe it, Hall et al. "examined organic-rich sediments exposed by recent retreat of the Marr Ice Piedmont on western Anvers Island near Norsel Point," where glaciers "have been undergoing considerable retreat in response to the well-documented warming." There, they "obtained moss and reworked marine shells from natural sections within 26 meters of the present ice front," as well as "both peat and reworked shells from sediments exposed in a tunnel beneath the residual ice mass," several samples of which were radiocarbon-dated and the results converted to calendar years.

What was learned
The three U.S. scientists report that "peat from the overrun sediments dates between 707 ± 36 and 967 ± 47 cal. yr B.P.," leading them to conclude that "ice was at or behind its present position at ca. 700-970 cal. yr B.P. and during at least two earlier times, represented by the dates of shells, in the mid-to-late Holocene."

What it means
In language pure and simple, Hall et al. say their findings mean that "the present state of reduced ice on the western Antarctic Peninsula is not unprecedented," which leads them to pose another important question: "How widespread is the event at 700-970 cal. yr B.P.?"

In answering their own query, the researchers respond that (1) "Khim et al. (2002) noted a pronounced high-productivity (warm) event between 500 and 1000 cal. yr B.P. in magnetic susceptibility records from Bransfield Basin," that (2) "dates of moss adjacent to the present ice front in the South Shetland Islands (Hall, 2007) indicate that ice there was no more extensive between ca. 650 and 825 cal. yr B.P. than it is now," that (3) "evidence for reduced ice extent at 700-970 cal. yr B.P. is consistent with tree-ring data from New Zealand that show a pronounced peak in summer temperatures (Cook et al., 2002)," that (4) "New Zealand glaciers were retracted at the same time (Schaefer et al., 2009)," and that (5) their most recent findings "are compatible with a record of glacier fluctuations from southern South America, the continental landmass closest to Antarctica (Strelin et al., 2008)."

In light of these several observations, it would appear that much of the southern portion of the planet likely experienced a period of significantly enhanced warmth that falls within the broad timeframe of earth's global Medieval Warm Period, as may be seen from a quick glance at the Interactive Map and Time Domain Plot of our Medieval Warm Period Project, which truly impressive interval of warmth occurred when there was far less CO2 and methane in the atmosphere than there is today.

References
Cook, A.J. and Vaughan, D. 2009. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere Discussions 3: 579-630.

Cook, E., Palmer, J. and D'Arrigo, R. 2002. Evidence for a "Medieval Warm Period" in a 1100-year tree-ring reconstruction of past austral summer temperatures in New Zealand. Geophysical Research Letters 29: 10.1029/2001GL014580.

Hall, B. 2007. Late-Holocene advance of the Collins Ice Cap, King George Island, South Shetland Islands. The Holocene 17: 1253-1258.

Khim, B-K., Yoon, H.I., Kang, C.Y. and Bahk, J.J. 2002. Unstable climate oscillations during the Late Holocene in the Eastern Bransfield Basin, Antarctic Peninsula. Quaternary Research 58: 234-245.

Schaefer, J., Denton, G., Kaplan, M., Putnam, A., Finkel, R., Barrell, D.J.A., Andersen, B.G., Schwartz, R., Mackintosh, A., Chinn, T. and Schluchter, C. 2009. High-frequency Holocene glacier fluctuations in New Zealand differ from the northern signature. Science 324: 622-625.

Strelin, J., Casassa, G., Rosqvist, G. and Holmlund, P. 2008. Holocene glaciations in the Ema Glacier valley, Monte Sarmiento Massif, Tierra del Fuego. Palaeogeography, Palaeoclimatology, Palaeoecology 260: 299-314.