Scientists studying the jet stream over Europe discovered that it has contributed to the extreme weather seen across the continent in the last 50 years.

Jet streams are rivers of wind, 5 to 9 miles up, in the high atmosphere. They’re caused by solar radiation heating rising air, which is then deflected sideways by Earth’s rotation.

They can move up to 275 miles an hour and are strong enough to push weather around and carry moisture, dust, or volcanic ash across oceans.

There are four jet streams on Earth: a polar and subtropical jet in both the Northern and Southern Hemispheres. And their paths can fluctuate.

When they drift toward the pole, they pull warmer air with them, causing hot summers and droughts in the middle of continents and rain in the subtropics.

When they drift toward the equator, they pull cold air from the pole, causing harsher winters in the midcontinent.

Scientists in Europe studied tree rings in the UK and the Mediterranean to analyze patterns of temperature and rain.

They found that, since 1960, the northern polar jet had drifted more frequently than in any period in the last 300 years, bringing droughts to the south and floods to the west in some years, and the opposite the next.

Climatologists theorize that a generally warming planet may be influencing the path of the jet stream. But most scientists agree that we really don’t know the cause.

It’s one more of those big mysteries blowing around, right here on Earth.