Atlantic Conveyor current slow to impact Europe, North American weather

REMEMBER Day after Tomorrow? One of the movie’s key plot-points is happening: The Atlantic conveyor currents have dramatically slowed.

An ice age freezes New York after it is flooded in the 2004 film The Day After Tomorrow. movies scene

REMEMBER Day after Tomorrow? One of the movie’s key plot-points is happening: The Atlantic conveyor currents have dramatically slowed.

The Gulf Stream currents draw warm water from the equator northwards, bringing with it extra warmth and humidity to Europe, Canada and North America — and pushing back the reach of chilled polar air in the process.

It’s actually why places such as England, Iceland and parts of Canada are as habitable as they are. The current brings with it a mass of relatively hot air in a giant, natural air-conditioning system.

The warm water — drawn from as far as the Indian Ocean — scoots along the surface. But once it reaches the far reaches of the North Atlantic, it cools. Having become saltier through evaporation, this water sinks and slinks back south in the ocean’s depths.

It’s why it’s called the Atlantic Conveyor.

The worldwide thermohaline circulation system draws warm water far into the Northern Hemisphere, making Europe and North America warmer than they would be. Source: NASA

But the cycle is changing. Fast.

“It is conspicuous that one specific area in the North Atlantic has been cooling in the past hundred years while the rest of the world heats up,” says researcher Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany.

Mystery cold patch: What’s going on in the North Atlantic? http://t.co/S389GnN2PH pic.twitter.com/FQdkoo5bHf

— Stefan Rahmstorf (@rahmstorf) March 23, 2015

Now he knows why.

“We have detected strong evidence that the global conveyor has indeed been weakening in the past hundred years, particularly since 1970,” he says.

Cool “blip” ... Trends in North Atlantic surface temperatures since 1901. Source: Nature Climate Change.

His study, published in the journal Nature Climate Change, shows a significant fall in North Atlantic water temperatures of up to 20 per cent in the past century. It argues this has been caused by an influx of up to 8000 cubic kilometres of freshwater between 1900 and 1970, exploding to 13,000 cubic kilometres between 1970 and 2000.

It’s happened before. Hugh volumes of freshwater have flooded into the North Atlantic from giant inland lakes left behind as an ice age retreated. When these lakes burst their ice or sediment barriers, they dramatically diluted the North Atlantic.

The effect was to force the downward suction of the saltier water further south. Or to stop it altogether.

So what’s causing it now?

The North Atlantic’s cooling surface. Source: Nature Climate Change

The researchers argue the two main sources of increased freshwater in the North Atlantic are melting icebergs from the shrinking Arctic Circle and the disappearing glaciers of Greenland.

“Now freshwater coming off the melting Greenland ice sheet is likely disturbing the circulation,” says co-author climate scientist Jason Box. “So the human-caused mass loss of the Greenland ice sheet appears to be slowing down the Atlantic overturning — and this effect might increase if temperatures are allowed to rise further.”

a conspicuous area of cold in a warming world http://t.co/mZYqhPnyhe

— Jason Box (@climate_ice) March 23, 2015

Unlike the movie, this won’t result in an instant ice age.

But it does trigger the process that would have eventually brought one on — if Earth wasn’t as warm as it is.

What it can do it change the weather. Substantially.

Exaggerated impact ... While sea levels will rise, it won’t be a tsunami.

Big chill ... Cold snaps will be more frequent and more intense, just not city-destroying.

Winter weather will become more intense without the moderating warmth of the conveyor. And the downward suction of the current would be removed.

Then there’s the ocean’s ecosystem.

The Atlantic Conveyor brings with it fresh nutrients from the tropics, delivering them to the North Atlantic fisheries. The deep, cold water carries nutrients from the deep back down south to feed the ecosystems there.

Any dramatic shift in this pattern has the potential to destroy entire fishing economies.

@JamieSeidel