´Medieval Warm Period should simply be named Medieval Period´

There is climatology and there is paleoclimatology. And then there is something in between. You thought yesterday´s trip to the early Pleistocene was geologically speaking exactly that, a trip to yesterday? Well, in that case today we go only a single minute back in time, to the late Holocene – or Middle Ages to be more precise.

Medieval Warm Period
The Medieval Warm Period and the Little Ice Age compared to the current climate warming, based on one of the typical hockeystick temperature graphs. This one is derived from IPCC’s 4AR from 2007 – and it resembles for instance the (newer) BEST temperature graph. (For extra dramatic effects extrapolate the line to above right to include all the even-hotter years of the 21st century.)

As we have learned from previous studies of the Holocene climate, the current warming is exceptional not only for its speed and magnitude, but also because of its planetary spread (as the warming results from increased heat absorption in the entire troposphere).

Other notable Holocene climatic fluctuations were more down to redistributions of cold and warm air due to temporarily changing air pressure patterns, which can for instance be influenced by Grand Solar Minima of the solar cycle.

As some of these late Holocene climate changes have impacted inhabited areas of West Europe, their scale may have previously been overestimated. This goes for the Little Ice Age – and, according to a group of American researchers, also for the preceding Medieval Warm Period, which is dated somewhere between 950 and 1250 AD.

Based on a temperature study using lake sediment measurements of algae fat deposits* from Kongressvatnet lake on Svalbard, Spitsbergen climate scientists William D’Andrea of University of Massachusetts’ Department of Geosciences concludes the Medieval Warm Period that historians can stretch to Viking travels to Iceland and South Greenland, and wine production on the British Isles, was not a big fluctuation further north – Spitsbergen, on the European border of the Arctic Ocean.

[*) Did you know algae produce more unsaturated fats in colder water, and more saturated fats in relatively warm waters? Best you should know, it is why cold water fish are loaded with those heart-healthy omega 3 fatty acids.]

D’Andrea – lead author of a study published in Geology – even argues the Medieval Warm Period would better simply be called the ‘Medieval Period’.

Due to factors like the albedo feedback climate warming is most pronounced at high latitudes. In the High North medieval temperatures do not compare to recent hot summers. The researchers not only find the recent summers have been the hottest in a 1800 year temperature record – also that the actual temperature height difference between recent summers and those of the Middle Ages is compelling: the summers on Svalbard of the last 25 years (since 1987 that is) have been 2 to 2.5 degrees Celsius warmer than those of the Medieval Period.

What’s more, the researchers have also found additional evidence that the Little Ice Age (LIA), which, depending on source, started directly after the Medieval Warm Period, or lasted from about 1550 (to 1850) – was a local climatic fluctuation too, affecting mostly the regions that are under influence of the North Atlantic Oscillation (NAO), like West Europe, and parts of Atlantic North America.

The glaciers on Spitsbergen did reach their maximum Holocene extent during the Little Ice Age, but this was not because it was colder, but because the winters were wetter [which makes perfect sense to a meteorology freak – simply study the negative NAO blockade map that is typical for cold West European winters during the LIA, with high air pressure over Scandinavia – and you see Svalbard would have had dominant westerly winds, with an Atlantic influence, not cold, but wet].

© Rolf Schuttenhelm | www.bitsofscience.org

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