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The Little Ice Age in West Antarctica
Reference
Orsi, A.J., Cornuelle, B.D. and Severinghaus J.P. 2012. Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West Antarctic Ice Sheet (WAIS) Divide. Geophysical Research Letters 39: 10.1029/2012GL051260.

Background
The authors write that "the Northern Hemisphere experienced a widespread cooling from about 1400 to 1850 C.E., often referred to as the Little Ice Age (hereafter LIA)," which they describe as "the latest of a series of centennial scale oscillations in the climate," citing Wanner et al. (2011). However, they say "it is still unclear whether the Southern Hemisphere high latitudes had a temperature response synchronous to that of the Northern Hemisphere," noting that "changes in the solar forcing" - which many scientists believe were responsible for driving the sequential climatic progression from Roman Warm Period to Dark Ages Cold Period to Medieval Warm Period to Little Ice Age to Current Warm Period - "would call for hemispheric synchroneity."

What was done
Working at a 300-meter-deep air-filled hole that had been drilled on the West Antarctic Ice Sheet (WAIS) Divide (79°28'S, 112°05'W) in January 2005, Orsi et al. employed a single thermistor -- which had been calibrated at Scripps Institution of Oceanography against a secondary reference standard that led to a relative uncertainty over the range of their measurements of 0.0023°C - to measure vertical profiles of temperature in January of both 2008 and 2009, which allowed them to develop a history of surface temperature at that location over the last thousand years.

What was learned
The three researchers, all from the Scripps Institution of Oceanography, report determining that "the WAIS Divide was colder than the last 1000-year average from 1300 to 1800 C.E.," and they say that "the temperature in the time period 1400-1800 C.E." - which meshes well with the chronology of the LIA in the Northern Hemisphere - "was on average 0.52 0.28°C colder than the last 100-year average."

What it means
Orsi et al. feel confident in stating that their result "is consistent with the idea that the LIA was a global event, probably caused by a change in solar and volcanic forcing, and was not simply a seesaw-type redistribution of heat between the hemispheres as would be predicted by some ocean-circulation hypotheses."

Reference
Wanner, H., Solomina, O., Grosjean, M., Ritz, S. and Jetel, M. 2011. Structure and origin of Holocene cold events. Quaternary Science Reviews 30: 21-22.

Reviewed 19 September 2012