Friday, February 8, 2013

“We can start calling it The Medieval Period again” – William D’Andrea


A paper recently published in the Journal “Geology”, has concluded that the summer temperatures on the Norwegian archipelago of Svalbard are now warmer than at any other time in the last 1,800 years – including the medieval warm period.

The naturally driven Medieval Warm Period, from about 950 to 1250 AD, has been a favourite time for people who deny evidence of anthropogenic climate change. The climate reconstruction from Svalbard casts new doubt on that era’s reach, and undercuts sceptics who argue that current warming is also natural. Since 1987, summers on Svalbard have been 2 degrees to 2.5 degrees C (3.6 to 4.5 degrees F) hotter than they were there during warmest parts of the Medieval Warm Period (D'Andrea, Vaillencourt et al. 2012).

The Svalbard Archipelago (77°–80°N) occupies an important location for studying patterns and causes of Arctic climate variability as it is situated between physically distinct ocean currents and air masses and along major conduits of oceanic and atmospheric heat transfer to the Arctic. As a result, climate modelling studies project that Svalbard will warm more than any other landmass by the end of the twenty-first century (Solomon et al., 2007) and hence its geographic location makes Svalbard important for understanding Northern Hemisphere climate dynamics.

The research was conducted through the analysis of unsaturated fat levels of algae buried in lake sediments. In colder water, algae make more unsaturated fats, or alkenones; in warmer water, they produce more saturated fats. Up until now, ice core data has been the main point of references for Arctic climate, but as ice cores are reliant on snowfall, they only represent cold season snowfall. Lake sediments, as in this study; with their record of summertime temperatures, can tell scientists how climate varied the rest of the year and provide a full, more detailed picture.

Very interesting indeed.

References:

D'Andrea, W. J., D. A. Vaillencourt, et al. (2012). "Mild Little Ice Age and unprecedented recent warmth in an 1800 year lake sediment record from Svalbard." Geology.

Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor,M., and Miller, H.L., eds., 2007, Climate change 2007: The physical science basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change: Cambridge, U.K., Cambridge University Press, 996 p

For access to the abstract go here (full text requires subscription):
http://geology.gsapubs.org/content/early/2012/09/18/G33365.1.abstract

Photo: Svalbard glacier, courtesy of William D’Andrea

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