It would be possible to predict the heat already in winter. At the core of the weather phenomenon is a cold patch of meltwater in the North Atlantic.
North sea ice in the polar region is shrinking as the climate warms. It won’t be long before the sea waves freely in late summer and autumn, when the ice area is at its smallest.
New research according to this, it happens ten years earlier than expected. The first ice-free day would fall in the current or the following decade.
Melting is also affecting Europe’s weather, another new study in the journal Weather and Climate Dynamics shows.
Climate scientist at the University of Colorado, USA Marilena Oltmans namely with his colleagues noticed the connection between melting and the continent’s hot summers.
To the mechanism associated with the so-called cold patch, which is an exceptionally cooling sea area located in the North Atlantic.
The patch is apparently created when the low-salt meltwater from both the Greenland ice sheet and the sea ice falls on top of the heavier salty water and the layers do not mix.
In this way, the heat cannot rise from deeper and the surface waters become colder than usual in autumn and winter.
Researchers estimated the extent of melting by measuring water salinity in different regions of the North Atlantic.
The measurements showed that the amount of meltwater varied widely in different winters, which indicated the melting during the previous summer. The more abundant meltwaters also strengthened the cold patch.
The patch affects European weather by increasing storms in the North Atlantic. Namely, the storms get their strength from the border zone between the cold area and the warm water further south.
Researchers noticed in their decades-long measurements that during strong patches the boundary to the southern waters was steeper. The westerly winds were stronger and the winters more stormy.
The strong westerly winds push the extension of the Gulf Stream, i.e. the North Atlantic Sea Current, further north around the British Isles.
As the change continues into the summer, the warm flow forms a barrier to the jet stream in the upper atmosphere. As a result of the fight, a zone of hot and dry air is parked in Europe.
Weather statistics provide support for the mechanism described by the researchers.
To test for its hypothesis, the group analyzed the ten hottest and ten coldest summers in Europe since 1980. It turned out that the hottest summers were preceded by abundant meltwater, while the coldest ones were not.
“If we had known this mechanism before, we could have predicted these summers in advance,” Oltmans says In an interview with the science magazine Nature.
He believes that the research opens up the possibility of predicting already in winter whether Europe will have a scorching hot summer.
Arctic melting has so far been linked to the exact opposite risk of heat, namely the cooling of Europe.
The melting waters are expected to slow down the North Atlantic circulation, which brings warm water from the south. The movement is maintained by the fact that the water, which has become heavier due to cooling in the north, sinks down and new water comes in from the south.
The melt waters slow down the sinking of the water, causing the current to slow down. This, in turn, can lead to a cooling of Europe, when the warm flow from the south slows down.