Valerie Trouet taking a pencil-thin core from an old Bosnian pine (Pinus heldreichii) growing on Mount Olympus in Greece. Photo: Greg King

The jet stream of the Atlantic has power over the weather for a significant part of the Northern Hemisphere, but how greatly it varies over long time frames has been an unanswered question.

Now, a new analysis of ancient tree rings in the British Isles has determined that the Jet stream has a huge effect on the climate of the entirety of Europe – and it’s been more variable over the last half century, they conclude in their paper in Nature Communications.

The tree rings date back to 1725. Over that time, the Jet’s directional swings had serious ripple effects on entire continents, but especially Europe, they report. The dendrochronological data show that when it is directed farther north, the Isles and western Europe have heat waves, while southeastern Europe has massive rains and flooding.

When it tilts southward, the opposite is true, they report.

“We find that the position of the North Atlantic Jet in summer has been a strong driver of climate extremes in Europe for the last 300 years," said Valerie Trouet, an associate professor of dendrochronology at the University of Arizona Laboratory of Tree-Ring Research. "Since 1960 we get more years when the jet is in an extreme position.”

Trouet first got the idea for the incisive look into the Jet stream while visiting her family in Belgium during the wet summer of 2012. While there was a surplus of rain in western and northern Europe at the time, news accounts showed the opposite was true in the northeastern Mediterranean.