Quantcast
Science
Goddard Media Studios / NASA

Slow Motion Ocean: Why Are North Atlantic Currents Weakening?

By Alex Kirby

The Gulf Stream is slowing, the North Atlantic is cooling. An international scientific study has found new and harder evidence that one of the planet's key heat pumps, the currents which exchange warmth between the tropics and the Arctic, are weaker today than at any time in the last thousand years.


The currents, known as the Atlantic overturning—its scientific name is the Atlantic Meridional Overturning Circulation (AMOC)—bring warm water north from the tropics and return south with cold water.

Earlier studies suggested strongly that any weakening of the AMOC would speed sea level rise on the U.S. east coast and cool north-west Europe by up to 5°C.

Those studies made use of computer simulations. But the latest research is radically different. It is based on direct observation of what is happening in the ocean. And it is, in non-scientific language, hard evidence that the Gulf Stream is slowing down.

A team from Germany's Potsdam Institute for Climate Impact Research (PIK) and the U.S. National Oceanic and Atmospheric Administration has found evidence which it says not only supports the earlier predictions, but makes them hard to dispute.

In a study published in the journal Nature the researchers say analysis of sea surface temperature data shows that the AMOC has slowed down by roughly 15 percent since the middle of the 20th century, with human-made climate change a prime suspect.

"We detected a specific pattern of ocean cooling south of Greenland and unusual warming off the U.S. coast—which is highly characteristic for a slowdown of the Atlantic overturning, also called the Gulf Stream system," said the lead author, Levke Caesar from PIK. "It is practically like a fingerprint of a weakening of these ocean currents."

For decades, computer simulations have generally predicted that the AMOC will weaken in response to human-caused global warming. But whether this is already happening has until now been unclear, because of a lack of long-term direct current measurements.

Most Robust

Not any more, though. "The evidence we're now able to provide is the most robust to date," said Stefan Rahmstorf of the Potsdam Institute, who conceived the study. "We've analysed all the available sea surface temperature data sets, comprising data from the late 19th century until the present."

"The specific trend pattern we found in measurements looks exactly like what is predicted by the computer simulations as a result of a slowdown in the Gulf Stream system, and I see no other plausible explanation for it."

The Atlantic overturning is driven by the differences in the density of the ocean water: when the warm, lighter water flows from south to north it becomes colder, denser and heavier, making it sink deeper and flow back southwards.

Global warming is not the only influence on the AMOC. Increased rainfall and meltwater from the Arctic sea ice and Greenland ice sheet are also diluting the waters of the northern Atlantic, reducing the salinity. Less saline water is less dense and so less heavy, making it harder for the water to sink from the surface to the ocean depths.

Second Study

There have been long debates about whether the AMOC could collapse, which would constitute a tipping element in the Earth system. The PIK study does not consider the AMOC's future, instead analysing how it has changed over the past century.

A second study, by a team including David Thornalley, from University College London, in the same issue of Nature, looks into the Earth's past climate to reconstruct Atlantic overturning changes over the past 1,600 years.

It provides independent confirmation for earlier conclusions that the weakness of the circulation today is unprecedented for more than a millennium at least.

"Several lines of evidence are coming together to a consistent picture now, all pointing at the same weakening since the 1950s," said Prof. Rahmstorf. "[They include] sub-polar Atlantic cooling, the warming inshore of the Gulf Stream, Thornalley's proxy data for subsurface Atlantic temperatures, and earlier proxy data from deep sea corals showing water mass changes in the Gulf of Maine."

Reposted with permission from our media associate Climate News Network.

Show Comments ()

EcoWatch Daily Newsletter

Sponsored
Popular
Sit-in at Rep. Hoyer's office. Sunrise Movement

1,000+ Youth Activists Storm Capitol to Demand Green New Deal

More than 1,000 climate activists with the youth-led Sunrise Movement stormed the U.S. Capitol in Washington and participated in sit-ins at Democratic leaders' offices on Monday.

The protesters demanded Reps. Nancy Pelosi, Steny Hoyer and Jim McGovern support Rep-elect Alexandria Ocasio-Cortez's proposal of a "select committee" for a Green New Deal before the winter recess.

Keep reading... Show less
Popular
The Stikine River runs through Wrangell, Alaska. Mining operations nearby threaten to poison fish in the Stikine watershed and destroy the traditions and livelihoods of Southeast Alaskan Tribes. Alaska Department of Fish and Game

Canada as Ugly Neighbor: Mines in BC Would Devastate Alaskan Tribes

By Ramin Pejan

Mining operations in Canada are threatening to destroy the way of life of Southeast Alaskan Tribes who were never consulted about the mines by the governments of Canada or British Columbia.

Keep reading... Show less
Business
Deforestation on peatland for palm oil plantation in Borneo, Indonesia. glennhurowitz / Flickr / CC BY-ND 2.0

World's Largest Palm Oil Trader Ramps Up Zero-Deforestation Efforts

The world's largest palm oil trader released plans on Monday to increase its efforts to eliminate deforestation from its supply chain.

Wilmar International, which supplies 40 percent of the world's palm oil, has teamed up with the sustainability consultancy Aidenvironment Asia to develop a comprehensive mapping database to better monitor the company's palm oil supplier group.

Keep reading... Show less
Popular
The Elkhorn Slough Reserve is one of California's few remaining coastal wetlands. Edmund Lowe Photography / Moment / Getty Images

New EPA Rule Would Sabotage Clean Water Act

By Jake Johnson

In a move environmentalists are warning will seriously endanger drinking water and wildlife nationwide, President Donald Trump's U.S. Environmental Protection Agency (EPA) is reportedly gearing up to hand yet another gift to big polluters by drastically curtailing the number of waterways and wetlands protected under the Clean Water Act.

Keep reading... Show less
Sponsored
Popular
James Braund / Getty Images

40 Acres of Farm Land in America Is Lost to Development Every Hour

By Brian Barth

Picture bulldozers plowing up pastures and cornfields to put in subdivisions and strip malls. Add to this picture the fact that the average age of the American farmer is nearly 60—it's often retiring farmers that sell to real estate developers. They can afford to pay much more for property than aspiring young farmers.

Keep reading... Show less
Energy

60,000 Liters of Oil Spills From Pipeline Into Brazilian Bay

About 60,000 liters (15,850 gallons) of oil spilled from a pipeline into the Estrela River and spread to Rio de Janeiro's famed Guanabara Bay over the weekend, according to Reuters and local reports.

The pipeline is owned by Transpetro, the largest oil and gas transportation company in Brazil, and a subsidiary of Petroleo Brasileiro (commonly known as Petrobras). Transpetro claims the leak resulted from an attempted robbery.

Keep reading... Show less
Sponsored
Popular
alvarez / E+ / Getty Images

Holiday Shoppers, the Planet Needs You to Take It Easy With Next-Day Shipping

By Jeff Turrentine

Back in 1966, the editors of Time indulged in a long-honored magazine tradition and published an essay in which experts made predictions about the future—in this case, the year 2000. By then, these experts prognosticated, a typical shopper "should be able to switch on to the local supermarket on the video phone, examine grapefruit and price them, all without stirring from her living room." But even so, they predicted, "remote shopping, while entirely feasible, will flop." Why? Because shoppers "like to get out of the house, like to handle the merchandise, like to be able to change their minds."

Keep reading... Show less
Climate
The Russia pavilion at the COP24 conference in Katowice, Poland. Beata Zawrzel / NurPhoto via Getty Images

COP24: U.S. Joins Saudi Arabia, Russia and Kuwait in Blocking Crucial Climate Report

The U.S. has thrown its hat in the ring with three other fossil-fuel friendly nations to block the COP24 talks from "welcoming" the landmark Intergovernmental Panel on Climate Change (IPCC) report that warned that we must reduce greenhouse gas emissions to 45 percent of 2010 levels by 2030 in order to limit warming to 1.5 degrees Celsius above pre-industrial levels, BBC News reported.

Keep reading... Show less
Sponsored

mail-copy

The best of EcoWatch, right in your inbox. Sign up for our email newsletter!