The best of EcoWatch, right in your inbox. Sign up for our email newsletter!
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.
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.
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.
EcoWatch Daily Newsletter
Wolves and Jaguars Are Already Threatened by Border Razor Wire As Trump Vetoes Bid to Block Emergency Wall Funding
President Donald Trump issued the first veto of his presidency Friday, overturning Congress' vote to block his national emergency declaration to fund a border wall that environmental advocates say would put 93 endangered species at risk. However, the president's decision came the same day as an in-depth report from UPI revealing how razor wire placed at the border in the last four months already threatens wildlife.
Yet another whale has died after ingesting plastic bags. A young male Cuvier's beaked whale was found washed up in Mabini, Compostela Valley in the Philippines Friday, CNN reported. When scientists from the D' Bone Collector Museum in Davao investigated the dead whale, they found it had died of "dehydration and starvation" after swallowing plastic bags―40 kilograms (approximately 88 pounds) worth of them!
By Joe Sandler Clarke
"Don't expect us to continue buying European products," Malaysia's former plantations minister Mah Siew Keong told reporters in January last year. His comments came just after he had accused the EU of "practising a form of crop apartheid."
A few months later Luhut Pandjaitan, an Indonesian government minister close to President Joko 'Jokowi' Widodo, warned his country would retaliate if it was "cornered" by the EU.
By Luis Torres
For some people who live along the U.S.-Mexico border, President Trump's attempt to declare a national emergency and extend the border wall is worse than a wasteful, unconstitutional stunt. It's an attack on their way of life that threatens to desecrate their loved ones' graves.
At least 150 people have died in a cyclone that devastated parts of Mozambique, Zimbabwe and Malawi over the weekend, The Associated Press reported Sunday. Cyclone Idai has affected more than 1.5 million people since it hit Mozambique's port city of Beira late Thursday, then traveled west to Zimbabwe and Malawi. Hundreds are still missing and tens of thousands are without access to roads or telephones.
"I think this is the biggest natural disaster Mozambique has ever faced. Everything is destroyed. Our priority now is to save human lives," Mozambique's Environment Minister Celso Correia said, as AFP reported.