Europe's 10 hottest and driest summers in the past 40 years have all come after a particularly large amount of fresh water was released from the Greenland ice sheet, meaning southern Europe will experience an especially hot summer this year. Maybe you are doing it.

They say this link occurs because the excess meltwater triggers a series of amplifying feedbacks that affect the strength and position of the atmospheric jet stream over Europe. Marilena Ortmans At the UK National Marine Centre.

“2018 and 2022 were the most recent examples,” she says. 2022 saw extreme heat and numerous bushfires across Europe, with high temperatures reaching 40°C (104°F) in parts of the UK for the first time.

These feedback effects, on top of the underlying warming trend from fossil fuel emissions, mean Europe will become even hotter and drier in coming decades as the melting of the Greenland ice sheet accelerates. Then Mr. Ortmans says:

“This is on top of the warming that is already happening due to increases in greenhouse gases,” she says.

Hotter heat waves and drier droughts are expected as the planet warms, but in some regions, such as Europe, recent heat waves and droughts have been even more extreme than climate modeling projects. Several studies have linked these extreme events to changes in the strength and position of the Arctic jet stream. The Arctic jet stream is a band of upper-level winds whose location and strength have a significant impact on weather.

But it's not clear what causes these changes, Ortmans says. Now, she and her colleagues are analyzing weather observations from the past 40 years, and the results show that extreme weather is ultimately the result of a period of increased ice melt in Greenland. It is said that there is.

“Observational statistical associations are very powerful,” she says.

The excess meltwater leads to a shallow layer of freshwater that extends south of the North Atlantic Ocean. This layer does not easily mix with the warm, salty ocean water below, causing the ocean surface to be colder than normal in winter.

This makes the gradient between this colder water and warmer water further south even more extreme, strengthening the weather front aloft. As a result, wind patterns strengthen, pushing warm water flowing northward, the North Atlantic Current, further north than usual. This further amplifies the temperature gradient.

“The front that forms between an area of ​​cold fresh water and an area of ​​warm ocean water is the main source of energy for storms,” ​​she says.

In a 2020 study, Ortmans suggested: This process leads to an increase in storms. during one winter.

Now, Oltmans' team suggests that these winter changes have lasting effects into the following summer. “Two years after the freshwater anomaly occurred, we are still seeing significant signs,” she says.

The researchers found that stronger temperature gradients lead to stronger jet streams across Europe, making the weather in southern Europe even hotter and drier. Then, as the unusually cold water recedes, the jet stream moves north, bringing hot, dry weather to northern Europe.

“We have discussed the individual links in this feedback chain before,” Ortmans says. “What we did in this study is bring these links together.”

Computer models miss this chain of feedback because they don't include factors such as large fluctuations in meltwater from year to year, she says.

“The association between Atlantic freshwater anomalies and subsequent European summer weather proposed in this study is interesting and relevant to current scientific research on long-term predictions of summer weather, especially “If that relationship holds true for future summers,” he says. adam scaife He works on long-term forecasts at the UK Met Office.

“I think this study is somewhat convincing,” he says. Fei Luo At the Singapore Climate Research Center. But when it comes to predicting summer weather, looking at the previous year's snowmelt isn't as helpful as looking at winter weather conditions, Luo said.

But Oltmans is confident enough to predict that Europe will experience more heatwaves and droughts in the coming years as Greenland's ice melts further in the summer of 2023. “I think southern Europe will experience strong heat anomalies this summer,” she says.

These are likely to become even more powerful in 2025, after which they will begin to impact Northern Europe. “We expect Northern Europe to experience another strong heatwave and drought, not this year, but in the next few years.”