Arctic ice melt could change Europe's climate

Posted: 7 April 2011

A massive, growing pool of icy meltwater in the Arctic Ocean is a wild card in future climate scenarios, with the potential to change European weather and marine life.

Estimated in 2009 at more than 7,500 cubic km - twice the volume of Africa's Lake Victoria - and growing, the water could flush quickly into the Atlantic with unpredictable effect when prevailing atmospheric patterns shift, as occurred most recently in the 1960s and 1990s.

The situation is one of many disquieting findings captured by project CLAMER, a collaboration of 17 institutes in 10 European countries to gather together the results of EU funded research into climate change and Europe's oceans and near-shore waters, and the Baltic and Black Seas.

The full synthesis will be presented at an international conference at the Royal Flemish Academy of Belgium, Brussels, in September.

Ocean currents

Oceanographer Laura de Steur of the Royal Netherlands Institute for Sea Research says a mostly clockwise wind pattern for the past 12 years in the Arctic has contained a pool of relatively fresh water from unusually high river discharge and melting sea ice. This is now contained largely in an area known as the Beaufort Gyre.

When the general atmospheric circulation pattern does shift, the fresh, cold water is expected to enter the North Atlantic, with unpredictable impact on an ocean current system important to both European weather and marine food chain. Signs of such an atmospheric shift appeared in 2009 but the episode was too short to cause a major flush.

Arctic Ocean sea ice breaking up in March. Photo © James Hannigan/UCAR

Says Dr. de Steur: "The volume of water discharged into the Arctic Ocean, largely from Canadian and Siberian rivers, is higher than usual due to warmer temperatures in the north causing ice to melt. Sea ice is also melting quickly - another new record low for ocean area covered was documented this past January by the National Snow and Ice Data Center...

"In addition, sea ice that is thinner is more mobile and could exit the Arctic faster. In the worst case, these Arctic outflow surges can significantly change the densities of marine surface waters in the extreme North Atlantic. What happens then is hard to predict."

Disaster film

The scenario echoes the premise of a controversial 2004 disaster film, "The Day After Tomorrow," which depicted catastrophic climate disruption worldwide, dismissed by Dr. de Steur as Hollywood absurdity.

"Ice ages occur on geological time scales of tens of thousands of years," she says. "However, large regional changes could be in store if the ocean circulation changes."

Many scientists are concerned about the future of the ocean circulation system that carries heat north to moderate the European climate.

Essentially, as warm water flows from the tropics to the North Atlantic, it cools and increases in salinity, making it heavier. At the north end of the current, near southern Greenland, these currents are cooled strongly by the atmosphere. This cold, dense oxygenated water sinks and cascades like poured cream south along the sea floor. Further south, it warms and rises, lifting nutrients essential to the marine food chain in the process, then flows north again.

It amounts to a giant "conveyor" known as the Atlantic Thermohaline Circulation, or THC.

Abrupt change

The hypothesis is that additional ice melting throughout the Arctic region would dilute northern saltwater and alter its density, causing the conveyor to slow.

According to Detlef Quadfasel of the Hamburg University's climate centre, changes in the THC could be abrupt, occurring over a decade or two, but more gradual change is expected. Most climate models predict a 20 per cent weakening of the current by the end of this century.

Scientists note that rising atmospheric temperature related to the build-up of greenhouse gases might at least temporarily counteract the cooling effect on Europe if North Atlantic underwater currents slow. However, the western edge of Europe, particularly the United Kingdom and Scandinavia, could cool substantially nonetheless.

Some 20 institutes from nine European countries, coordinated by the Institution of Oceanography at the University of Hamburg, are now cooperating in extensive studies of the THC.