Penalties, Taxes, Storms, and the Jet Stream

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A A few years ago, Valerie Trouet, a tree scientist from Belgium, began to notice something strange. While his summer vacation was marred by cold rainy days, countries like Greece and Italy in the Eastern Mediterranean appeared to be struggling with drought and unusual heat. The opposite also appeared to be true—the hot, dry summer in Belgium and the British Isles was matched by the cool, wet weather of southeastern Europe. Trouet began to wonder if the jet stream, that narrow stream of air that circles the earth, had anything to do with it.

Jet streams are strong groups of air in the upper atmosphere that form at different latitudes at the boundaries of the world’s air currents. The strongest currents are around the polar regions, where warm air meets cold air from the Arctic and Antarctic regions. In the north, the position and shape of the jet stream is determined by the strength of the high and low weather systems that occur seasonally in the European continent. Most of the time, the jet stream flows in a relatively straight line, maintaining cold pressure systems in the north and warm pressure systems in the south. But in some years, the structure can waver or rise into waves, forcing colder and wetter conditions in the southeastern Mediterranean and pushing warmer weather to the northwest. (There is a similar tension between Southern California and the Pacific Northwest.)

Epidemics spread rapidly during unseasonably warm summers.

While researching, Trouet learned that several climate models suggest that this northern continental jet stream is shrinking with ongoing climate change, a process that can increase the frequency of simultaneous extreme weather conditions in different parts of the continent, including heat waves, droughts. , floods, and wildfires. If the models are correct, such extreme conditions could cause repeated crop failures in many parts of the continent at once. But many of these climate models rely on data collected after the 1980s, when satellite-based observations became widely available.

In order to gain a better long-term understanding of the jet stream and climate, Trouet decided to collaborate with historians and climate scientists. In a recent edition for Naturehe and his team developed a model of jet stream variability that extends the record by 700 years. By studying tree rings, Trouet and a team of paleoclimate experts proposed a change in the climate of summer from 1300 to 2004 AD They examined historical records to see how these weather conditions were reflected in records of storms, plagues and harvests. back to the Middle Ages. The researchers believe that their findings suggest a link between jet stream anomalies and seemingly unrelated events such as wildfires in Greece and Turkey, the spread of the plague in Ireland, and the increase in wine taxes in Medieval Hungary.

“It was a constant treasure hunt,” says co-author Ellie Broadman, an arborist and climate scientist who works at the Western California Ecological Research Institute.

To reconstruct the historical patterns of the jet stream, Trouet and his colleagues relied on trees from three regions: the Scottish Highlands in the northwest, the mountains of Europe, and the Bosnian pine growing in the south -east of the Mediterranean. The tree cores were studied for their “recent wood density,” which appears as a dark line separating the tree rings. The color, shape, and chemical composition of this dark region depends on the summer climate. Years of severe drought and heat waves result in dark and irregular lines. “We also looked at fire scars, where you can count on how many years there has been a wildfire,” says Broadman.

With the help of historians, Broadman and his colleagues were able to uncover information about the frequency of plagues, storms, and fluctuations in crop prices within their areas of interest. south-east and north-west Europe. Each time, they chased after watching at the same time. “It was either a passive response or an expected response for everything we looked at,” Broadman says.

In Britain in the Middle Ages, they found that epidemics spread rapidly when the summer, according to their models, was unusually warm, when fleas and people were on the move. In those same years, a fall in grape harvests and high wine prices were reported in the Balkans, possibly due to cold temperatures. Historical grain price reports from the Netherlands, Belgium and the British Isles for barley and wheat also suggest that crop failure rates were high during the years when the lines were restored. trees to indicate unusually cool weather.

“While there’s no very satisfying way to go back in time and say, ‘I know for sure that these things are related in some way,'” Broadman says, “I hope a huge number , a variety of completely different records. completely different times and types of documents,” that cement relationships. “It seems too much to be a coincidence.”

Currently, climate scientists disagree on whether the jet stream will decrease or reverse with continued climate change. “There are mixed opinions,” says Rachel White, a professor of atmospheric science at the University of British Columbia, who was not involved in the study. Much remains to be discovered about what drives the water jet, White says.

However, Trouet and his colleagues say their results suggest that we need to consider changes in the jet stream when considering the risks associated with climate change. future, including global food security. Seven hundred years of data is worth considering.

Artist: Oana Liviu / Shutterstock

• Elena Kazamia

  Written by November 21, 2024

  Elena Kazamia is a science writer from Greece. He holds a master’s degree in conservation from University College London and a Ph.D. in plant sciences from the University of Cambridge in the UK

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