Study tracks links between melting ice cap, Atlantic Ocean currents
FRISCO — The retreat of sea ice caused by global warming could lead to colder weather for parts of northwestern Europe, Canadian researchers said after studying changing ocean dynamics in the North Atlantic.
The new research reinforces previous findings that the shrinking Arctic ice cap is likely to change the delicate balance between the cold and dense water pouring out of the Arctic and the warm waters of the subtropical Atlantic, according to professor G.W.K. Moore, of the University of Toronto Mississauga.
“A warm western Europe requires a cold North Atlantic Ocean, and the warming that the North Atlantic is now experiencing has the potential to result in a cooling over western Europe,” said Moore.
The retreating sea ice may alter the oceanic convection process that keeps the conveyor belt of warm water flowing toward Europe. If oceanic convection decreases, the Gulf Stream may weaken, thereby reducing the warming of the atmosphere, in comparison to today, he said.
The research, published in Nature Climate Change, looked closely at changes the air-sea heat exchange in the region brought about by global warming, and to consider its possible impact on oceanic circulation, including the climatologically important Atlantic Meridional Overturning Circulation.
Previous studies have focused on the changing salinity of the northern seas and its effects on ocean circulation.
Moore and his fellow researchers based their findings on wintertime data from 1958 to 2014 that was provided by the European Centre for Medium-Range Weather Forecasts and model simulations.
Traditionally, the Gulf Stream moves warm water north toward western Europe, where it loses heat and moisture to the atmosphere, acting to moderate the climate in this region. The resulting colder, denser water sinks and returns south at a great depth eventually rising to the surface in the tropics, where the cycle, known as the Atlantic Meridional Ocean Circulation, begins all over again.
The Iceland and Greenland Seas are among the only places worldwide where conditions are right and this heat exchange is able to change the ocean’s density enough to cause the surface waters to sink. The largest air-sea heat exchange in these seas occurs at the edge of the sea ice.
In recent years, the sea ice has retreated, changing the area of maximum heat exchange. As a result, there has been a reduction in the heat exchange over the locations where sinking occurs in the ocean. This has the potential to weaken oceanic convection in the Greenland and Iceland Seas.
“The heat exchange is weaker … it’s like turning the stove down 20 percent,” says Moore. “We believe the weakening will continue and eventually cause changes in the Atlantic Meridional Overturning Circulation and the Gulf Stream, which can impact the climate of Europe.”
The paper’s other authors are Kjetil V?ge from the University of Bergen, Robert Pickart from Woods Hole Oceanographic Institution and Ian Renfrew from the University of East Anglia.