Nature Climate Change on June 29 published groundbreaking new research that quantifies the degree to which a warming Arctic climate and the loss of sea ice is weakening air-sea heat transfer and ocean currents, including the Gulf Stream, that keep western Europe warmer than it would otherwise be.
Led by University of Toronto Mississauga (UTM) atmospheric physicist Prof. G.W.K. Moore, an international research team determined that the loss of Arctic sea ice is reducing the exchange of heat between air and sea and hence flows of cold, dense ocean water south to the Equator, a process known as oceanic convection. Near the equator, the waters in these deep ocean currents rise and are warmed. They then flow north, fueling the Gulf Stream and Atlantic Meridional Overturning Circulation (AMOC) currents.
Reductions in these flows portend a much colder Western Europe, as well as other potentially profound changes. “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,” Moore stated.
A weaker Gulf Stream and colder Europe?
Moore and colleagues in the U.K., Norway and the U.S. carried out the first study that measures changes in the exchange of heat between ocean and atmosphere in the Greenland and Iceland Seas where the cold Arctic Ocean waters that fuel the Gulf Stream and AMOC originate. Analyzing data from 1958-2014 they determined that climate warming is driving loss of Arctic sea ice, which, in turn, is reducing air-sea heat exchange and the flow of cold, dense waters that fuel the Gulf Stream and AMOC.
Data from the Greenland and Iceland Sea waters the climate scientists studied are from the areas where the maximum amount of heat is exchanged between the ocean and the atmosphere. It's typically cold enough to increase the density of ocean waters there enough so that they sink to great depths. The largest of these areas is at the fringes of sea ice.
These areas of maximum air-sea heat exchange have been shrinking in recent years as Arctic sea ice retreats. That has resulted in less heat being exchanged, which holds the potential to weaken oceanic convection.
“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.”
Image credits: 1) NASA; 2) "Decreasing intensity of open-ocean convection in the Greenland and Iceland seas"
G. W. K. Moore, K. Våge, R. S. Pickart & I. A. Renfrew; Nature Climate Change