The melting of the Greenland ice sheet is causing more extreme heat in Europe, contributing to the major heatwaves experienced there so far this year. The surge of cold meltwater into the North Atlantic is altering ocean temperatures and shifting the jet stream to favour heatwaves in western Europe and the Mediterranean, a study undergoing peer review has found. As Greenland ice loss accelerates, Europe may suffer more frequent and intense heatwaves than climate models currently predict.
This newly discovered “atmospheric bridge” played a major role in the unprecedented heatwaves this summer, according to Marilena Oltmanns at the UK’s National Oceanography Centre, who is one of the study’s authors. Drought and heat push Europe’s power grid to breaking point “Europe heats up faster. This is because of the jet stream shift,” she says.
In the future we will think this [year’s heatwave] was not a heatwave; this was nice.” The steady rise in global temperature has increased heatwaves. But it’s still debated whether changes in prevailing weather patterns are also contributing. In the past 30 years, high-pressure ridges – large areas of elevated air pressure that look like a ridge or upside-down U on weather maps – have been forming more frequently over Europe, the study finds, leading to sunny skies and extreme heat.
These ridges are caused by waviness in the jet stream, the band of strong winds that circles the northern hemisphere. When the more or less straight-flowing jet stream meanders northward around western Europe, it allows warm air from the central Atlantic and Sahara desert to pour into the ridge that’s been created. Years with extensive high-pressure ridges over Europe have resulted in heatwaves like the one that killed 70,000 people in 2003.
The researchers say the formation of the ridges can be traced back to Greenland through a cascade of climate events. In the summer before years of extensive ridging, an average of 81 billion tonnes more meltwater rushes off the ice sheet, they found. The cold meltwater lowers sea surface temperatures as it spreads through the North Atlantic in the autumn and winter.
Its freshness inhibits mixing with saltier, warmer deep layers, further cooling the surface. These pulses of meltwater cooling come on top of the “cold blob,” a long-term decline in ocean temperatures in the North Atlantic that some scientists blame on the weakening of the Atlantic Meridional Overturning Circulation (AMOC) system of currents. Together, they create a sharp temperature front between the cold waters and the warmer surface waters further south in the Atlantic.
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