New Study: Atlantic Circulation Less Stable than Thought (“Gulf Stream” slowdown)

January 5, 2017

New study on behavior of Global warming’s effect on critical circulation in the Atlantic Ocean – what many laypeople think of as “the Gulf Stream”, but scientists more correctly call the “Atlantic Meridional Overturning Circulation”, or AMOC.

I produced the video (above) not long ago on a similar study by Stefan Rahmstorf, Mike Mann, and Jason Box – which looked at the possible effect of melting Greenland ice on the same circulation.  The current study looks at greenhouse gases and global temps generally, but does not include Greenland melt.

Main point is, while most folks think of global warming as a long, slow process, climate change can have unexpected, paradoxical, and sudden effects, as it can cause relatively rapid changes in ocean and/or atmospheric circulation.

Science News:

Spewing too much carbon dioxide into the atmosphere could shut down the major ocean current that ferries warm water to the North Atlantic, new climate simulations suggest. While not as extreme as the doomsday scenario portrayed in the movie The Day After Tomorrow, such a shutdown could cause wintertime temperatures to plummet by an estimated 7 degrees Celsius or more in northwestern Europe and shift rainfall patterns across the globe.

Many previous climate simulations predicted that the Atlantic circulation would remain largely stable under future climate change. But those simulations failed to accurately portray how relatively freshwater flows between the Atlantic and Southern oceans, an important mechanism as the climate warms. After fixing that inaccuracy, Yale University climate scientist Wei Liu and colleagues set up an extreme climate scenario to test the current’s robustness. Doubling CO2concentrations in the atmosphere shuttered the Atlantic current in 300 years, the researchers’ simulation showed.

While such a rapid CO2 rise is unrealistic, the new simulation demonstrates that the current isn’t stable after all, the researchers conclude January 4 in Science Advances. “The next step is to use a more realistic warming scenario to predict what the future will look like,” Liu says.

Even with a more realistic scenario, the applicability to the real world will be hampered by a lack of direct long-term observations of the Atlantic circulation, says Gerald Meehl, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo. Observations help improve simulations, but such data for the Atlantic current don’t go back “for more than a decade or two,” he says.

Known as the Atlantic Meridional Overturning Circulation, the Atlantic current is a colossal conveyor belt. It carries warm water from the South Atlantic northward along the ocean surface into the North Atlantic. Near Greenland where the current makes a U-turn, cold water sinks and flows southward into the South Atlantic. These two halves of the AMOC form a loop that keeps northwestern Europe warm and drives rainfall across the tropical Atlantic.

Warming due to climate change in the North Atlantic makes the waters there less dense and less likely to sink. This change slows the AMOC. In many previous climate simulations, the current’s speed bounces back. That’s because these simulations incorrectly show that rain-freshened water flows from the Southern Ocean into the Atlantic Ocean. In these simulations, as the AMOC weakens, this influx of freshwater slackens and the Atlantic becomes saltier. Like cold water, salt-laden water is denser and more likely to sink, helping the AMOC recover.

But ocean observations show that freshwater flows from the Atlantic into the Southern Ocean, not the other way around. Liu and colleagues updated an existing simulation by manually correcting the flow direction. After doubling CO2 concentrations in the simulation compared with 1990 levels, the researchers found that the North Atlantic warmed and the AMOC slowed. With less warm water moving northward, countries such as England and Iceland cooled even when taking into account the greenhouse warming from the added CO2.

The researchers also found that as the AMOC slowed, less freshwater from the Atlantic flowed into the Southern Ocean. That decreased the Atlantic’s saltiness, further weakening and ultimately collapsing the AMOC. The same simulation without the flow-direction change did not show a disrupted current, the researchers found. Meltwater from shrinking Greenland ice may also freshen the Atlantic, suppressing the AMOC, though the researchers didn’t look at this effect.




31 Responses to “New Study: Atlantic Circulation Less Stable than Thought (“Gulf Stream” slowdown)”

  1. Tom Bates Says:

    In the medieval warm period it was warmer than today. They used to grow grapes in places like Dorset so the warm currents were not cut off. The actual caused of the change in the climate from the medieval warm period to the little ice age is unknown, the reason the little ice age has pretty much gone away is also unknown. Maybe all these models are so much horse pucky if they cannot explain known climate change in the last few thousand years with data at hand.

    • vierotchka Says:

      They have been growing grapes in Dorset since the Roman times, and still do. For example:

    • You’re an interesting sorta stupid aren’t ya Tom?

    • vierotchka Says:


      Vines have been grown in the British Isles since before the Romans arrived and, following the Norman invasion of 1066, became a feature of monastic life and the gardens of royalty and nobles. However, they were rarely if ever commercial, and wine production was always very limited. The revival of viticulture, which started in 1945 and gathered pace in the 1960s and ’70s, was based upon different grape varieties and production techniques, and this has resulted in vineyards today being a significant feature in the agricultural landscape of Great Britain.

    • The idea of a globally warm Medieval Warm Period has been discredited for several years. More representative samplings of temperatures show that Dorset, to the extent that evidence is interpreted correctly, was an outlier in an otherwise cooler than average world.

      The information is so well known, that even Wikipedia has a reasonable treatment.

    • redskylite Says:

      Computer modelling is used in just about all branches of science and industry theses days, to dismiss it as “horse pucky” is nonsensical.

      I am sure you benefit from computer modelling most days of your life. If you drive a modern car over of a modern bridge on the way to a modern building, then congratulations – you have benefited from computer modelling.

      Might just as well call University lecturers and books of knowledge “Horse plucky” and return to the 17th Century.

      As for the MWP and LIA the global-ness and relevance to the industrially created build up of greenhouse gases (that we have today) is vastly overstated by trolls.

      ´Medieval Warm Period should simply be named Medieval Period´

  2. redskylite Says:

    To put it all in a simple analogy, I finally gave up smoking tobacco because I was scared of getting lung cancer, (my wife nagged me a lot).

    Would the good folks of Dorset, Devon, Somerset and Cornwall (plus surrounding counties) want to risk lose their blessed mild winter climates, by burning more and more fossils.

    No of course they would not, not even a 1% chance.

    So convert to modern technologies and reject coal and fossil fuels. It’s a piece of cake.

    No shit.

  3. redskylite Says:

    I would just like to add a great article I read in the Atlantic today, great journalism and the topic well discussed.

    Americans who are concerned about climate change have long found themselves in an unenviable position: They have to debate about the existence of a debate.

    • The implications of being in such a position — which is basically that others have veto power over the best anyone can do — are actually pretty straightforward. Like it or not they are that these decisions will not change until there is irrefutable damage from the natural systems which are being so forced, with huge consequences for the innocents on the planet who did nothing to cause this, and the moral responsibility will lie wholly and incontrovertibly upon those who delayed, and quibbled, and enjoyed The Good Life fossil fuels and the Consumption Industry brought to them.

      The best anyone can do is Oppose, but wisely (being sure to live to fight another day), and live with as little impact as they can. And they should fully realize by doing what they do that they are not part of the culpable, and that, when the day of reckoning comes, it will be time to put notions of (Christian and other) charity aside, passing judgment on those who were effectively guilty of mass murder, let alone the wholesale destruction of species and ecosystems.

      Yeah, I know, we already have a lot to answer for and there remain systems in society which continue atrocities.

      But it is all we can do, and we can take satisfaction, even smug satisfaction in that. We should.

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