Global warming is slowing down the circulation of the oceans


Chris Mooney of the Washington Post reports the latest news on the climate crisis. Global warming is now slowing down the circulation of the oceans — with potentially dire consequences:

Last week, we learned about the possible destabilization of the Totten Glacier of East Antarctica, which could unleash over 11 feet of sea level rise in coming centuries.

gulf_streamAnd now this week brings news of another potential mega-scale perturbation. According to a new study just out in Nature Climate Change by Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research and a group of co-authors, we’re now seeing a slowdown of the great ocean circulation that, among other planetary roles, helps to partly drive the Gulf Stream off the U.S. east coast. The consequences could be dire – including significant extra sea level rise for coastal cities like New York and Boston.

A vast, powerful, and warm current, the Gulf Stream transports more water than “all the world’s rivers combined,” according to the National Oceanic and Atmospheric Administration. But it’s just one part of a larger regional ocean conveyor system – scientists technically call it the “Atlantic meridional overturning circulation” — which, in turn, is just one part of the larger global “thermohaline” circulation (“thermohaline” conjoins terms meaning “temperature” and “salty”).

For the whole system, a key driver occurs in the North Atlantic ocean. Here, the warm Gulf Stream flows northward into cooler waters and splits into what is called the North Atlantic Current. This stream flows still further toward northern latitudes — until it reaches points where colder, salty water sinks due to its greater density, and then travels back southward at depth.

This “overturning circulation” plays a major role in the climate because it brings warm water northward, thereby helping to warm Europe’s climate, and also sends cold water back towards the tropics.

[H]ere’s a wonderful video from NASA that visualizes the thermohaline circulation for the entire globe. Rahmstorf also has a blog post up at explaining his research.

* * *

What keeps everything churning in the North Atlantic is the fact that cold salt water is more dense than warm water — so it sinks. However, if too much ice melts in the region — from, say Greenland — a freshening of the cold salt water could occur. If the water is less salty it will also be less dense, reducing its tendency to sink below the surface.

This could slow or even eventually shut down the circulation. In the scientifically panned 2004 blockbuster film “The Day After Tomorrow,” it is precisely such a shutdown that triggers a New Ice Age, and utter global disaster and chaos.

That’s not going to happen, say scientists. Not remotely.

Nonetheless, the new research finds that global warming does indeed seem to be slowing down the circulation. And while hardly catastrophic, that can’t be good news. Among the very real effects, notes the Potsdam Institute’s Rahmstorf, could be a possible increase in U.S. sea level if the whole circulation were to break down — which would be seriously bad news for cities like New York and Boston.

The study uses a reconstruction of sea surface temperatures in the North Atlantic to find that starting in around 1970 or 1975, the overturning circulation started to weaken — an event likely triggered by an unusual amount of sea ice traveling out of the Arctic ocean, melting, and causing freshening. The circulation then started to recover in the 1990s, but  “it seems this was only a temporary recovery, and now it’s actually further weakened,” says Rahmstorf.

The hypothesized reason for further declines presented by the paper is that the massive Greenland ice sheet may now be losing enough freshwater due to melting to weaken the circulation. And indeed, it appears that a particular ocean region of the North Atlantic south of Greenland and between Canada and Britain is becoming colder — an indicator of less northward heat transport.

* * *

So far, the study finds, we’re looking at a circulation that’s about 15 to 20 percent weaker. That may not sound like much, but the paper suggests a weakening this strong has not happened at any time since the year 900. Moreover, this is already more weakening than scientifically expected — and could be the beginning of a further slowdown that could have great consequences.

The U.N.’s Intergovernmental Panel on Climate Change, in 2013, said it was “very likely” that the Atlantic overturning circulation would weaken over the course of this century, but gave a gigantic range of from 1 to 54 percent, with best estimates at 11 and 34 percent. We’re already in that window, suggests the new study, and it’s only 2015. So what would happen if the circulation weakens even more substantially or even shuts down?

One thing that will not happen from a shutdown of the circulation is a sudden, dramatic freezing of Europe. It will certainly cool, relative to a world in which the circulation remains robust — but that will be offset by rising average temperatures due to global warming, says Rahmstorf. The “Day After Tomorrow” scenario will not come to pass.

However, there are many other effects, ranging from dramatic impacts on fisheries to, perhaps most troubling of all, the potential for extra sea level rise in the North Atlantic region.

That may sound surprising, but here’s how it works. We’re starting out from a situation in which sea level is “anomalously low” off the U.S. east coast due to the motion of the Gulf Stream. This is for at least two reasons. First, explains Rahmstorf’s co-author Michael Mann of Penn State University, there’s the matter of temperature contrast: Waters to the right or east of the Gulf Stream, in the direction of Europe, are warmer than those on its left or west. Warm water expands and takes up more area than denser cold water, so sea level is also higher to the right side of the current, and lower off our coast.

“So if you weaken the ‘Gulf Stream’ and weaken that temperature contrast…sea level off the U.S. east coast will actually rise!” explains Mann by e-mail.

* * *

Indeed, researchers recently found a sudden, 4-inch sea level rise of the U.S. East Coast in 2009 and 2010, which they attributed to a slowdown of the Atlantic overturning circulation. Rahmstorf says that “for a big breakdown of the circulation, [sea level rise] could amount to one meter, in addition to the global sea level rise that we’re expecting from global warming.”

Shutting down the circulation would also almost certainly have effects on global weather — changing around major planetary heat transport processes tends to do that — though scientists don’t know yet what those would look like.

So in sum: It appears that we’ve just seen yet another surprise from the climate system — and yet another process, like the melting of Antarctica, that seems to be happening faster than previously expected. And indeed, much like with that  melting, the upshot if the trend continues is an especially bad sea level rise for the United States — the country more responsible than any other on Earth for the global warming that we’re currently experiencing.

This reporting does not address the dramatic changes in weather a slowdown or cessation of  the “Atlantic meridional overturning circulation” would cause. That will have serious repercussions for agricultural production and the world’s food supply. It will lead to deforestation and desertification of previously productive agricultural land. And there will be dramatic repositioning of human populations as communities are overtaken by rising oceans and changing climates.


  1. Steve, my screen isn’t showing a reply button, so I’ll start a new thread but this is in response to your last comment.
    If you read any of the articles that I sent links to you for, you would find that it was not one scientist that rejected the great myth being promulgated in conservative circles that the sun is heating up the planets, but MANY scientific studies that have investigated this idea and found that it is not happening, not to our planet, not to other planets, not to the moon. I do not have “an author” I have mentioned (among other sources) one author who was a conservative skeptic who did his own study with money from the oil industry and, much to their shagrin and his, found that NONE of the natural explanations fit with the warming being observed and the only explanation that did was rising Carbon dioxide from manmade emissions. That is reality.

    Now as to your idea that the solutions would “punish” successful countries, far from it. At every turn polluting industries have fought regulations but each and every time once they clean up their acts they actually earn more money than their dirty rivals. The problem is the short attention span of industry, driven by the quarterly profit statement and the tendency of corporate profiteers to want to drive every penny out of a business in the fastest time possible, right before they go bankrupt. When longer term thinking is applied cleaner industry generates higher profits than polluting ones. But only if the playing field is level. That’s where government regulation becomes necessary, to provide that level playing field. The free market doesn’t work unless it is also fair.

    now your argument about loss of standard of living is mythical. Denmark and Germany have embraced renewable energy, have put in place regulations that make the marketplace work, and have some of the highest standards of living in the world. Germany has already reached its 2020 goal of 30% of its energy coming from renewable sources. Dude, Germany is roughly at the latitude of Anchorage, Alaska! Their attention to climate change has yet to affect their standard of living — unless by standard of living you mean the freedom to pollute regardless of the effects on The climate and the health of your neighbors. As a matter of fact you could argue that it has protected their standard of living by making them less vulnerable to climate change AND future energy needs. And one other thing, if we do not move forward with investment in fighting climate change, i.e. renewable, non-carbon intensive energy generation then we WILL fall behind other countries economically as they make great leaps in the future economy of the world. We have already lost our solar module production plants to China and Germany because of lack of investment during the Bush years. The longer we hide our heads in the sand the farther behind we get. The rest of the world will not wait for us to catch up.

    • TS, I want to thank you for the calm and steady manner in which you have presented your arguments. Normally, by this time, my adversary has resorted to using profanity and name calling to sway me. It is a pleasure to encounter someone who doesn’t do that in presenting their argument.

      You are very persuasive, but I am still skeptical that mankind is the scourge causing the climate change. I admit I could be wrong, but the scientific evidence is still too squishy to convince me. But thanks for a spirited discussion!

      • The evidence is not even close to squishy. To say it is overwhelming is an understatement. Your ideology is getting in the way of the facts. When carbon that accumulated underground over tens of millions of years is put into the atmosphere in the last two centuries, most of it in the last 50 years, the impact is not surprising at all. It must be ideology, because you seem willing to accept the science that has revealed climate change throughout geologic history and the reasons for it, but not the science that explains what is happening and why over the last 50 years. Let me guess, you also listen to the 1 doctor in 100 who says nothing is wrong with you, when the rest say you have a terminal disease.

    • Ha! Ha! There are certain subjects of interest to me where it does appear that way. In fact, I sometimes feel a little guilty at taking up so much space on the blog. But look at the bright side: I am good target for all the of those who disagree to attack my positions (and/or me) which I would huess must be fun for them. Always having someone agree with you all the time must be boring, I would think.

  2. “The good thing about science is that it’s true whether or not you believe in it.” Neil deGrasse Tyson

    Steve, The job of science is to discover and explain how the natural world works. Not to explain it to your liking. The above evidence actually explains why the eastern part of north america has been colder than normal while the western portion and much of the rest if the world has been way warmer than normal. If you understood science rather than Republican soundbites you would see the connection.

    Considering how crappy the pay is in science (yes it is) and how much crap scientists get from everybody who doesn’t like what they discover, and how easily a false research paper can be disproven, it is amazing that you think that 97% of the world’s climate researchers (100% of the non-oil funded ones) would perjure themselves before their peers in order to get crappy money that they could easily trade for tenfold as much by saying the opposite and getting paid by big oil.

    By the way if you really feel science is so disconnected from reality go ahead and take penecillin for the next penecillin-resistant infection you get. Surely it will work just as well, afterall those scientists who found penecillin-resistant organisms were just trying to improve their reputations and their livelihoods, not trying to find the truth. The scientific process that led to both discoveries is EXACTLY the same. 1) Ask a question 2) generate a hypothesis 3) test the hypothesis 4) if the evidence supports the hypothesis submit your work for peer review 5) peers not only review the work, and rip it to shreds if it doesn’t work, but also repeat your experiment to make sure your conclusion is correct 6) if your work survives keep working to make your hypothesis even more accurate 7) if after thousands and thousands of other researchers and experiments have demonstrated over many years that the hypothesis is comprehensive, accurate, and applies broadly to the natural world it may be upgraded to being called a theory. If after many many many researchers have reached the same conclusion by wildly different experiments in different fields, the theory becomes a widely accepted theory. That is where we now stand with global climate change. The only thing left is to try to determine the timeframe. previous projections appear to have been too slow, it is happening much faster than originally predicted.

    • I am very aware of the scientific method and peer review. I am also aware that scientists are human beings and subject to the whimsies, social pressures, desire for approval and personal ego trips inherent in all of us. AND I am aware that science has been used to further political ends numerous times in our history. It hasn’t been that long since science “proved” that the earth was flat, that the earth was the center of the universe, that reading bumps on the head could tell what kind of person you were, that blacks were inferior to whites, that women were inferior to men, et al. Scientific fraud is not unheard of even with the scientific method and peer review.

      I do not deny there is climate change going on. What I object to is the willingness – no, the eagerness – of scientists to blame mankind, and the United States in particular, for the changes. The evidence for that conclusion has never been demonstrated. Even the scientists preparing the evidence do so in squishy terms such as “possibly”, “maybe”, “might” “could be”, “points to”, etc. However they have no problem taking their squishy evidence and making firm declarations that it is mankind creating the problem. That is a leap of faith that is not justified based on an objective review of the evidence.

      Scientists are human beings. They like being told “good job” and the current political climate (no pun intended) only does that for scientists who determine mankind is responsible. Those who issue the grants for research are not looking for objective scientists to determine if it is mankind’s fault because, in their minds, the issue is resolved. They look for scientists to study how much mankind is affecting the climate. There is a big difference there. Scientists are not fools. If you want to earn a living in your field, you need grant money and you tailor your application to meet the requirements of the grantor.

      I don’t want people’s lives adversely affected by actions taken to curtail mankind’s possible effect on climate change “just in case” there “might” be a connection. At the current time it is more of political issue than a scientific issue. You only have to objectively read the “evidence” in this article to see that. The author uses squishy language about what might be happening without attributing a source for the change, and then in the last paragraph he condemns the United States for being “King Global Warming”. Where did he get that conclusion? Certainly not from his own evidence. THAT is my objection to this whole debate…climate change has become a quasi-religion requiring more faith in it’s conclusions than science.

      • Dude, um, Steve, you haven’t got a clue how science really works. There has been tons of research to find the cause of climate change aka global warming, most it trying to find a natural cause, and ALL potential natural sources of global warming have been discovered to be too small to have caused it. Even famed climate change skeptic and physicist, Richard Muller, who conducted his own study, intending to rebuke other climate scientists,systematically found that nothing could explain it but human emitted greenhouse gases. See this article:
        His funding came from the fossil fuel industry much to their unhappiness.

        The science newswriter quoted in the article is also correct that the largest portion of all human greenhouse gases that have been emitted were emitted by the U.S. That is a fact. It could change in the future, especially if the U.S. were to embrace renewable energy, but as of now it is a true statement. What you are objecting to is the WAY that he said it. Too bad. He’s a news writer, writing an editorial, he gets to phrase it however he wants. What you are really objecting to are the facts of climate change.

        • With your obviously great knowledge on this issue, where does the fact that the sun is running through a hot cycle right now and is warming ALL the planets fit?

          • If you read Muller’s article you will find that his team examined solar influences and found them to be negligible. A compilation of studies looking into this question have found that in fact the solar cycle and the climate are moving in opposite directions. See this article:

            Here is the bottom line on climate change/global warming that conservatives will appreciate, we MUST fix it eventually, the longer we wait the more expensive it gets. The cheapest fix is to stop using greenhouse gas-producing energy generation. By the way, nuclear fuels generate at least 50% of their energy from greenhouse gas production due to the use of fossil fuels in the mining, production, and life cycle disposal of the fuel and spent fuel. The cheapest form of renewable energy is conservation, which returns $3 for every $1 invested. After that solar and wind are now be on on par with average fossil fuels prices. As a person whose roof has solar panels I can tell you that there is no difference in our life, it generates energy without any effort or attention on our part, and reduces our electric bill. That is why the major utilities are unhappy about it.

          • You can’t dismiss the effect of the sun’s warming as easily as that. There are other studies that have demonstrated it IS a significant factor. Enough of a factor that it is raising the temperature on the other planets and moons as well. I am not surprised the your author minimized that effect because that would undermine their basic premise: That mankind is the culprit and the only solution is to punish those countries that are successful.

            I applaud your use of solar panels. I think the increasing use of solar and wind energy is a good thing. I also think getting away from the internal combustion engine is a good idea, as well. What I object to is the idea that some governmental agency will come down and start punishing the United States for our success with draconian measures that hurts our standard of living based upon conjectural science that has bent the science so as to arrive at a pre-determined conclusion. There is an enormous amount of national jealousy and liberal guilt wrapped up in the climate change debate that is occurring. It ignores similar past climate changes before man was even here and has the arrogance to assume mankind has the power to cause such massive changes.

  3. ”…the United States…[is]…the country more responsible than any other on Earth for the global warming that we’re currently experiencing.”

    All your authors waffling and tepid expressions of “seems to be”, “might”, “possibly”, “could be”, “is perhaps”, etc., and yet he ends his article with a definitive condemnation of the United States as the evil overlord of global warming. While climate change does seem to be occurring, this race to condemn mankind, and the U.S. in particular, is a rush to judgment. I think one of the biggest problems is that too many people have their reputations and their livelihoods attached to “proving” mankind is responsible for any truth to emerge.

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