It’s remarkable how often “medieval” is used as an all-purpose insult in public discussion and popular culture. But it’s a special curse word in climate studies because the notion of an unprecedented late-20th-century crisis depends in significant part on downplaying the extent and even existence of temperature variations and warm intervals in previous centuries. Michael Mann’s “hockey stick” graph tried to get rid of the well-known “Medieval Warm Period” entirely and Al Gore sneered at it. Less drastic attacks depicted it as a local European phenomenon. But a new study confirms what common sense long suggested: like other warmings (and coolings including the Little Ice Age) it was, indeed, global. Better blame human deforestation or something because the dang thing just won’t go away.
We’ve long known there was a Medieval Warm Period for various reasons including the famous Viking voyages of exploration and settlement in places like Iceland and Greenland. Also from records of what was grown and where and when. But it is true that the best records came from the place that actually had the Middle Ages, namely Western Europe. So it’s important to get data from elsewhere. And now people are.
The latest study in that vein is the work of Sebastian Lüning and Fritz Vahrenholt, whose The Cold Sun argued for a powerful solar influence on climate fluctuations, along with Mariusz Gałkab of the Department of Geobotany and Plant Ecology at the University of Lodz. And it looks at the continent as far from Europe as you can get, Antarctica, and finds warming between 1000 and 1200.
It also finds cooling. It finds the complex picture climate presents to anyone not a zealot. In short (this excerpt being from their abstract)
“A generally warm MCA [Medieval Climate Anomaly] compared to the subsequent Little Ice Age (LIA) was found for the Subantarctic Islands south of the Antarctic Convergence, the Antarctic Peninsula, Victoria Land and central West Antarctica. A somewhat less clear MCA warm signal was detected for the majority of East Antarctica. MCA cooling occurred in the Ross Ice Shelf region, and probably in the Weddell Sea and on Filchner-Ronne Ice Shelf. Spatial distribution of MCA cooling and warming follows modern dipole patterns, as reflected by areas of opposing temperature trends. Main drivers of the multi-centennial scale climate variability appear to be the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) which are linked to solar activity changes by nonlinear dynamics.”
So there’s that wretched sun again, as well as those terrible Middle Ages.
As Pierre Gosselin comments, “With the publication of this paper, the Medieval Climate Anomaly (MCA) has now been confirmed on all four continents of the southern hemisphere.” As he also notes, it’s complicated. “While the largest part of the southern hemisphere apparently experienced a warm phase during the MCA, there were also isolated areas that cooled down.” But acknowledgement of complexity is not cause for mental paralysis. Climate is not simple. But it does fluctuate broadly. And there was a Medieval Warm Period and it happened just about everywhere.