Natural Sciences

Jet stream changes linked to more extreme weather events since the 1960’s.

There has been intense debate as to whether extreme weather events and the increased variability of the jet stream is connected to climate change and part of this debate has been due to the lack of historical data.

However, scientists from the University of Arizona and Swiss Federal Research (WSL), reconstructed historical changes in the position of the North Atlantic Jet Stream up to 290 years in the past, by studying data from ‘tree-rings’ in trees located in the British Isles and the North Eastern Mediterranean. The ‘latewood’, which forms towards the end of the annual growing season and the density of this wood, reflects August temperatures in any one year.

They analysed the late summer weather going back to 1725 and determined the historical positions of the jet stream between 1725 to 1978. For the period 1979 to 2015 they relied on meteorological observations.

They concluded that the position of the North Atlantic Jet Stream in summer is shown to be a strong driver of climatic extremes in Europe for the last 300 years according to V. Trouet, a lead researcher.

They also reported that the swings in position of the North Atlantic Jet Stream became more frequent in the second half of the 20th century and since the 1960’s there has been an unprecedented rise in the number of years when the North Atlantic Jet Stream has been in an extreme position. An extreme position is linked to extreme weather events.

In an extreme northerly position, the British Isles and Western Europe experience extreme summer temperatures and South Eastern Europe heavy rains and flooding; in an extreme southerly position, a reversal is experienced, with Western Europe experiencing heavy rains and flooding, South Eastern Europe extreme high temperatures, drought and wildfires.

These extreme events such as heat waves, drought and flooding are happening on top of increasing temperatures and global warming according to the authors of the research.

The team are hoping to reconstruct the path of the North Atlantic Jet Stream for up to 1000 years in the past by analysing older trees since found in the Balkans and in the United Kingdom.

This article was attributed and provided by PG International

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