Map view of Europe.
January 31, 2016

Europe’s summer weather is the hottest seen in two millennia

It looks like investing in European sunscreen might be a smart business move, as a new study has found that the continent’s summer temperatures over the last three decades have been the highest ever seen in the past 2,100 years.

The study, which can be found in Environmental Research Letters, drew this conclusion after examining historical evidence along with evidence found in the rings of trees. All the trees had been alive for at least 700 years, and dated anywhere between 500 BCE and modern times. They also spanned the continent; researchers collected data from from Spain, France, Switzerland, Austria, Romania, Finland, and Sweden.

The international team of 45 scientists from 13 countries discovered that, over the course of the last two millennia or so, temperatures have varied widely. During Roman times until the third century CE, summers were generally warm. For three hundred years after that, things were generally cooler—followed by a warmer medieval period. Then, the Little Ice Age followed, bringing temperatures down during the 14th to 19th centuries.

Modern increases in temperature

The most recent time periods, though, have been marked by continuous and unusual temperature increases that mark a sharp contrast to past climate shifts. The past 30 years in particular have shown a significant increase in temperature from decades before, totaling 2.34 degrees Fahrenheit (1.3 degrees Celsius)—which not only lies well outside the natural temperature variation, but included more heat waves than before.

“Our primary findings indicate that the 1st and 10th centuries CE could have experienced European mean summer temperatures slightly but not statistically significantly (5% level) warmer than those of the 20th century,” wrote the authors in the paper. “However, summer temperatures during the last 30 years (1986–2015) have been anomalously high and we find no evidence of any period in the last 2000 years being as warm.”

Moreover, their evidence suggests that temperature fluctuations between warm and cool periods over the past two millennia were bigger than we thought, meaning that the models we currently use to understand climate across the centuries may be underestimating temperature changes throughout history. In particular, the models may predict fewer heat waves than what we've seen. But this knowledge may be the key to solving this issue.

“We now have a detailed picture of how summer temperatures have changed over Europe for more than two thousand years,” said the coordinator of the study, Professor Jürg Luterbacher from the University of Giessen in Germany, in a statement, “and we can use that to test the climate models that are used to predict the impacts of future global warming.”

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