Thursday, December 01, 2016

Climate record reveals cruelty of an unusually cold decade in 15th century

What was the climate of the Europe's Low Countries -- modern-day Belgium, northern France, Luxembourg and the Netherlands -- during the 15th century? That's what historian Chantal Camenisch was trying to find out when she happened upon evidence of cruel cold spell.

"I realized that there was something extraordinary going on regarding the climate during the 1430s," Camenisch, a postdoctoral researcher at the University of Bern in Switzerland, said in a news release.

She found historical records of icy wine, frozen rivers and lakes, unusually late frosts and ruined crops. Winters went long, often into April, while summers were moderate and brief. Seed stocks were damaged, growing seasons shortened.

"For the people, it meant that they were suffering from hunger, they were sick and many of them died," said Camenisch.

Camenisch recruited a team of researchers for further analysis. Evidence from tree rings, ice cores and lake sediments corroborated the historical record -- the 1430s were unusually cold.

"The reconstructions show that the climatic conditions during the 1430s were very special," said Kathrin Keller, a climate modeler at the Oeschger Centre for Climate Change Research in Bern. "With its very cold winters and normal to warm summers, this decade is a one of a kind in the 400 years of data we were investigating, from 1300 to 1700 CE."

The researchers don't yet have an explanation for the decade-long cold spell.

"Was the anomalous climate forced by external influences, such as volcanism or changes in solar activity, or was it simply the random result of natural variability inherent to the climate system?" Keller asked.

In their paper on the period -- published this week in the journal Climate of the Past -- researchers revealed the different ways communities responded to the difficult climate.

"Famine and epidemics led to an increase of the mortality rate," the authors wrote. "In the context of the crisis, minorities were blamed for harsh climatic conditions, rising food prices, famine and plague."

Larger, more diverse cities responded more constructively, but scientists say the episode is reminder of the necessity for preparedness. Though it's possible a similar period of cold could settle upon a normally temperate region, extreme heat and drought are more likely risks.

"Compared to the 15th century we live in a distinctly warmer world," Keller said. "As a consequence, we are affected by climate extremes in a different way -- cold extremes are less cold, hot extremes are even hotter."

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