Climate scientists have noticed a disturbing pattern in the North Atlantic. This is the relative cooling of surface waters in the area fed by the Gulf Stream. This pattern has emerged over recent decades, and may portend very rapid and potentially disruptive climate change in the upcoming decades. The cooling is not subtle at all, and looks like this:
So what does this mean? A paper out just today describes, explains, and discusses this odd anomaly and its potential consequences. First, a bit of context.
The Earth’s climate follows certain patterns. Most obviously it is warmer at the equator, colder at the poles. Less obvious if you’ve not looked into this is the presence of a very wet band around the middle of the earth, flanked to the north and south by irregular dry bands (that’s where most of the deserts are), with these flanked by the temperate zone, where you have more moisture and highly seasonal temperatures, and so on.
This pattern emerges as a complex response to two major inputs. First the Earth is spinning, and second, the Earth is heated more at the equator than the poles, so heat must move through air and water currents towards the north and south.
One of the major systems that moves heat away from the equator is known sometimes as the Atlantic Conveyor, which is really part of a lager system of sea currents that includes the Gulf Stream. Notice that the Indian Ocean is sequestered mostly in the Southern Hemisphere, bordered along the west by Africa and the north by Asia. Extra warm water in the Indian ocean tends to make its way around the southern tip of Africa, and up the Atlantic, which is a round about route. This water eventually makes its way to the North Atlantic, where it cools, and owing to evaporation, becomes extra salty. This drives the formerly warm surface water into the depth of the ocean, where it flows along the bottom of the Atlantic south, eventually returning (I oversimplify a bit) to the Indian Ocean and elsewhere.
This system is also known as the AMOC (Atlantic Meridional Overturning Circulation) and is part of the global “Thermohaline Circulation” system.
Meanwhile, a smaller but similar aspect of this system starts with the Gulf of Mexico. This water becomes quite warm from the Sun, but is blocked from moving directly north by the presence of North America, with Florida adding to the captive nature of those waters. But the water does make its way around Florida and flows north along the East coast of the US, and eventually also reaches the North Atlantic, and similarly, contributes to the saline deep currents.
Because salinity partly, even largely, drives this system, adding fresh water to the North Atlantic may interfere with this system of currents. How do you get enough fresh water to do this? In the past, huge volumes of fresh water probably entered the North Atlantic every now and then as large outflows of giant inland lakes, formed by melting glaciers, broke through barriers of ice or sediment. There is some evidence that in the past this sort of thing may have partly, or even completely, shut down the Atlantic Conveyor system, which would have had huge impacts on climate.
Today there seems to be two main sources of extra fresh water in the area. One is during years (or decades) when there is a larger than usual number of ice bergs floating into the North Atlantic from the Arctic. The other, potentially, is from melting of Greenland’s fast glaciers, a process that has recently speeded up because of human caused greenhouse gas pollution warming the Earth.
By now you may recognize this scenario as the basis for the Hollywood disaster movie “The Day After Tomorrow.” In that movie the thermohaline circulation system shut down and an ice age instantly gripped the planet. Giant frozen tornadoes came plummeting down from the Stratosphere. One of them hit the helicopter the British Royal Family was escaping in. Everybody in the US ended up in Mexico.
Every one who survived, that is.
The thing is, now, this can’t happen. Well, that particular scenario can’t ever really happen. But yes, the shutting down of this system can theoretically cause the onset of an ice age, or at least a mini-ice age, and has done so in the past. But no, it can’t now because our planet has warmed too much from human greenhouse gas pollution to allow that to happen. That may be the one good thing about global warming.
The new research does suggest, though, that this major pattern of circulation appears to be slowing down. This will have a number of effects. It will likely change the weather in Europe a bit. It will likely cause an increase in sea level along the US East Coast, because the current (and former) system piles up water towards the east and lowers it in the west, within the North Atlantic. That could be worth a few inches.
According to lead author Stefan Rahmstorf, “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. Now we have detected strong evidence that the global conveyor has indeed been weakening in the past hundred years, particularly since 1970,” says Rahmstorf. If the slowdown of the Atlantic overturning continues, the impacts might be substantial. Disturbing the circulation will likely have a negative effect on the ocean ecosystem, and thereby fisheries and the associated livelihoods of many people in coastal areas. A slowdown also adds to the regional sea-level rise affecting cities like New York and Boston. Finally, temperature changes in that region can also influence weather systems on both sides of the Atlantic, in North America as well as Europe.”
The researchers used a combination of sea surface, atmospheric, and proxy (mainly coral) indicators of temperature to indirectly measure changes in ocean currents over time.
According to climate scientist Jason Box, “Now freshwater coming off the melting Greenland ice sheet is likely disturbing the circulation. 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.” Michael Mann, another author of the paper, adds, “Common climate models are underestimating the change we’re facing, either because the Atlantic overturning is too stable in the models or because they don’t properly account for Greenland ice sheet melt, or both. That is another example where observations suggest that climate model predictions are in some respects still overly conservative when it comes to the pace at which certain aspects of climate change are proceeding.”
What happens if the system actually turns off completely? It was formerly thought that the chances of this happening were small, but this research, conforming to a growing body of expert opinion, suggest that the chances of that may be higher than previously thought. Were this to happen the main characteristic of any effects would be rapidity. Whatever happens would happen fast, and rapidly changing climate is generally regarded as bad no matter what the change itself really is.
A criticism of this work has emerged, suggesting that another study indicates that there is no a long-term slowdown of the Atlantic Meridional Overturning Circulation (as suggested by the research covered here). That criticism is incorrect. Michael Mann, one of the AMOC study's author has written a clarification on his facebook page. He begins:
Some critics have tried to make hay over a previous article from last year by URI Graduate School of Oceanography scientist Tom Rossby (see: http://www.gso.uri.edu/b…/rossby-gulf-stream-is-not-slowing/) they claim contradicts our recent Nature Climate Change study finding evidence for a long-term slowdown of the Atlantic Meridional Overturning Circulation ("AMOC"). ...
Rossby employs direct measurement of Gulf Stream transport using a ship-board acoustic Doppler current profiler (ADCP) over the interval 1993-2012. I have no reason at all to doubt Rossby's findings. And they do *not* conflict with our own findings (though some have misleadingly sought to assert they do) for two fundamental reasons:
Mann's entire post is HERE and you should go read it.
Rahmstorf, S., Box, J., Feulner, G., Mann, M., Robinson, A., Rutherford, S., Schaffernicht, E. (2015): Evidence for an exceptional 20th-Century slowdown in Atlantic Ocean overturning. Nature Climate Change (online) [DOI: 10.1038/nclimate2554 ]
Stefan Rahmstorf, lead author, has this blog post at RealClimate: What’s going on in the North Atlantic?
Figure caption from the original article, goes with the graphic at the top of the post:
Figure 3. Surface temperature time series for different regions. Data from the proxy reconstructions of Mann et al.12,13, including estimated 2-σ uncertainty bands, and from the HadCRUT4 instrumental data49. The latter are shown in darker colours and from 1922 onwards, as from this time on data from more than half of all subpolar-gyre grid cells exist in every month (except for a few months during World War II). The orange/red curves are averaged over the subpolar gyre, as indicated on Fig. 1. The grey/black curves are averaged over the Northern Hemisphere, offset by 3 K to avoid overlap. The blue curves in the bottom panel show our AMOC index, namely the difference between subpolar gyre and Northern Hemisphere temperature anomalies (that is, orange/red curves minus grey/black curves). Proxy and instrumental data are decadally smoothed.
A neat video of the thermohaline circulation system.
A movie produced by Peter Sinclair, that goes along with THIS blog post.
Coverage by Chris Mooney at the Washington Post: Global warming is now slowing down the circulation of the oceans — with potentially dire consequences
Other posts of interest:
- [Important new meta-study of sea level rise in the US.](http://scienceblogs.com/gregladen/2014/09/05/important-new-meta-study-o…)
- [Whatever you thought about sea level rise, it’s worse than you were thinking.](http://scienceblogs.com/gregladen/2013/12/05/whatever-you-thought-about…)
- [How high can the sea level rise if all the glacial ice melted?](http://scienceblogs.com/gregladen/2013/06/18/how-high-can-the-sea-level…)
- [Bangladesh and Sea Level Rise](http://scienceblogs.com/gregladen/2013/04/29/bangladesh-and-sea-level-r…)
Also of interest: In Search of Sungudogo: A novel of adventure and mystery, set in the Congo.
Also of interest: In Search of Sungudogo: A novel of adventure and mystery, set in the Congo.
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If it happens it seems like Western Europe and Eastern N.A. are going o be in for a lot more cold weather and that, particularly in Europe bodes ill for agriculture. I wonder what the effect will be over here in the west of N.A.
Answer: Our reservoirs are just about almost DRY. Also bodes ill for agriculture, I might add...
Is the phenomena an delayed effect of the great Greenland warming during first part of the 20th century up to 1950, as the effect are most pronounced during the period 1970-90? The AMOC have recovered slightly after 1990 when the current warming of the Arctic is most pronounced. The period 1960 - 1985 was cold in that part of the Arctic, the direct connection with melting glaciers on Greenland is not obvious.
No, it is likely an effect of freshening in the North Atlantic involving an increase in nearly 20 thousand cubic kilometers of fresh water between 1961 and 1990. This is primarily due to anomalous sea-ice export from the Arctic, but also increasing river discharge into the arctic ocean and discharge from the Greenland Ice sheet (meltwater and ice bergs). The fresh water does not clear very fast so it tends to accumulate.
This might be the paper Dr. Mann mentioned on his Facebook page a few days ago. It was still embargoed, so he did not go in to details but he noted that a serious disruption in part of the Atlantic is observed, but not modeled well. If the current "shuts down," it will leave heat in regions that currently get cooled by the current.
Some day I would love to read good news regarding human-caused climate change.
This is so misleading. Greenland is a geothermal hot spot. The Ground has been heating up in the mantle and that has increased ice melt. Iceland has had a dramatic increase in magma movement as well. Geothermal heating is also the reason for the ice melt in the western part of Antarctica.
[John, there are a few geothermal hot spots under some glaciers. There is absolutely no evidence suggesting anything about change over time in this as a factor, and the glaciers have only recently started melting at a higher rate. The geothermal cause of melting is considered minor. Also, Iceland is not actually in Greenland. So, no, unfortunately global warming caused by humans does not get of the hook. Now you know! -gtl]
The study is published in the journal Nature Geoscience.
“The area of greatest and most recent glacier retreat is located in the northeastern portion of Greenland and is associated with a very linear NNE trending bedrock valley termed the Jacobshavn Glacial Valley (see locator map above).
NASA’s Study shows that this glacier was flowing very slowly down the valley and at the same time started gaining ice mass until 1998. At that point, it quickly started flowing down the valley while simultaneously losing large amounts of ice mass.
It is clear that the Jacobshavn Valley is geologically fault bounded, and has recently become geothermally active. All the data and observations fit this notion, so a sudden increase in fault-related heat flow would cause bottom melting of the glacier.
Also of significant relevance to the geologically induced geothermal heat flow of Greenland is a recently published research project by the GFZ German Research Center for Geosciences.
John, if you copy-paste something from another website, it would be nice if you indicate that.
Of interest in your copy-paste is he claim that the Northeast Ice Stream (I know, I know, not what it says, but that is the actual name of the ice stream in the northeast that drains about 15% of the GIS) comes from a "bedrock valley termed the Jacobshavn Glacial Valley". This surprised me quite a bit. I am 100% certain that the Jakobshavn Ice Stream is in the *west* of Greenland, so it would be rather weird to call the region in the northeast "Jakobshavn Glacial Valley". In fact, I am willing to say that the geologist that wrote the piece you partly copy-pasted needs a refresher course in geography...
He also just claims, without even a shadow of evidence, that there has been in increase in geothermal activity.
You did the same, claiming, without providing any evidence, that there has been a "dramatic increase in magma movement" for Iceland.
I want John to explain how geothermal activity *beneath* the Greenland glaciers (how many kilometers thick?) is causing unusual numbers of melting pools to form on TOP of the glaciers. "This is so misleading."
Oh, how many people think that man is that a huge factor to influence Earth climate....
And they think they are the one and only 'owners' of the truth, superior than others who believe otherwise....The way you replied to "John" says it all....Like he ever meant that Iceland and Antarctica (why did you leave Antarctica out of your ironic reply?) are the same place as Greenland...
Get it in your narrow minds finally: EARTH had always had climate cycles. From cold to warm, into Ice Ages and back.
That's beyond human activity. If it was not, explain to us why the Ice Ages were over. Why those glaciers melt. Was it the ...cars and factories of Homo Erectus? What was it?
How do you explain the Middle Age warm period? Were there factories then, too?
After that Warm Period Earth went into cooling again and now it's back to warming.
Mankind was able to monitor climate in the 20th century, during this warming period. So everybody thinks "whooah, the planet is warming, it's our fault". Probably supposing that before climate was a stable line! Well, it wasn't.
It just happened that we started monitoring into a warming period.
If we had started monitoring into a cooling period, all you would think that our 'greenhouse gases' make climate colder.
THAT's how "sophisticated" your beliefs are.
For God's sake, let Earth do its thing.
You? You might influence it by 0.000000000001%.
Chris, your assertions are incorrect and unfounded. Read all of he posts here and get back to us with specific questions:
Yes the Earth has many many cycles and one of the big contributors of all things in and around the Atlantic is the Atlantic Multidecadal Oscillation . You can find some info here. http://en.wikipedia.org/wiki/Atlantic_multidecadal_oscillation#/media/F…
It's started it's flip back to cold ... hmmm sound familiear .. oh yea... this article metions nothing about it.
Considering that we have only been measuring accurately the Ice sheet in Greenland relatively recently, I think everyone is way overreacting. Also it is a fact that we are in an interglacial period. Now Go Look it all up. Do your homework and stop reading blogs that scream about the Koch Brother conspiracies for gods sake. SMH
John, word to the wise: "Don't believe everything you think."
And the Koch Brothers don't need to engage in any conspiracies; they have more than enough money to act directly by and for themselves and their own self-centered interests.
Brain Here is a word to the intelligent. If you all want to have some credibility, I suggest staying away from blogs that spew conspiracy theories and stick to more credible sources. LOL Really... The science is settled... Right? When there are clearly many accredited scientists and even previous believers that say Human Caused global warming is a fraud.... SMH. That is the argument of the closed minded Lemmings. My mind is open, if there were not proof and admission that the global warming data has been doctored then I would could see such a staunch belief. The truth is that every day that argument loses ground. I know that those that blindly believe will follow to the end but I can hope that there are some people that will keep one eye open to other facts.
This blog does not spew conspiracy theories; it's chock-full of credible sources and links. Why not read a few?
No one said the science is settled. I'd rebut that if I saw it published, as would the blog owner here, and the science-types who frequent it. The science is evolving over time, as is characteristic of sciences of all types. This does not mean that we do not have results yet that provide sufficient understanding and the basis for forging sane policy.
Name an accredited scientist who calls AGW a fraud. Go ahead, try... We'll wait.
Science is the antithesis of being closed-minded. It's about studying "what is", and the rules of the game are that you report the results as they are, whether they affirm your political agenda or fail to (as in the case of AGW and what you subscribe to).
However, I will agree to your statement in #14, "Human Caused global warming is a fraud…. is the argument of the closed minded Lemmings." Yes, yes it is. Those with open minds examine the science as it stands today and realize the truth and their arguments of fraud lose ground, yes. Those who blindly believe the self-interested purveyors of fear, uncertainty, and doubt will follow them to a disastrous end, but I can hope that there are enough people who will keep one eye open to the objective, scientific facts and not rely on "their own set of facts" -- as you seem to endorse.
Look Brain... I'm going to leave you with this... http://www.wsj.com/articles/climate-science-is-not-settled-1411143565
he worked for the Obama administration and has taught physics in california institute of tech. I'm not going to list them all because you can do that yourself. if you are as open as you profess yourself to be, you already know. The problem I see there is that if that really was the case, then you're position would not be as ingrained as it is. Regardless, I do invite you to look up as much as you can on Steven E. Koonin. If you find some hidden conspiracy on him, I'll be waiting to offer another. enjoy your tin foil hat!
Looks like John is doing the usual shtick of not responding to the actual questions and criticism.
So when I link to a criticism of two actual climate scientists, showing Koonin to use political rather than scientific argumentation, John will likely run to yet another meme:
Kerry Emanuel... the guy that predicted hurricanes are getting more severe. Okay... Then you'll tell me Koonin is getting paid by some Oil company then I'll tell you that Emanual is getting paid by Federal grants to MIT. Then... I'll tell you that there are others at MIT "Dr. Richard Lindzen" for one that states the same thing and has said it publicly. with inside knowledge then you'll come back with the same argument. And it goes around and around and around. The truth is that the data has been doctored and continue to do it. People have admitted it. Nasa was only 38% sure it was the warmest year when those article were published. You guys have fun with all that go down with the ship. SMH... It's really pathetic actually. Ciao!
... I’ll tell you that there are others at MIT “Dr. Richard Lindzen...."
Science is a community effort, done by scientists. When all of the world's scientists agree except one, the odds are excellent that the one scientist is wrong--- not always, but 99.9999% of the time. Look at how many scientists cite Lindzen as an authority for anything; now look at Lindzen's publishing history. There is a reason why Lindzen publishes his astonishing discoveries only on blogs and not in science journals; there is a reason scientists don't cite Lindzen as anything other than an example for bad science. Ditto for Roy Spencer.
When you trot out Lindzen, you revealed how weak and silly your complaints are. If your complaints were valid you would be able to cite actual scientists working in actual science venues. Heh! Good luck with that,
John, accusing scientists of having doctored data is a very serious thing. If it is false, and it is, then it is libel. I just want you to understand that if I'm asked to provide information about who made this comment (you) then I'll do so. This is to give you an opportunity to retract your statement that scientists have doctored data.
Your statement about NASA misrepresents what they said, and is also fairly irrelevant. If I had a student test the significant of a trend by estimating the difference between the last point on that trend and the population I'd assign a low grade for that effort.
John writes: Look Brain… I’m going to leave you with this…
"This" is an essay in the Wall Street Journal. True, it's by a scientist who worked for the Obama administration. You should be careful about claiming that as an imprimatur of lack of bias; many scientists working for the Obama administration are holdovers from the G. W. Bush administration.
Then there is the fact that it's a WSJ essay. You should know the WSJ's history of such opinion pieces. It is not reassuring.
But let's cut to the chase. It's really very simple.
* Carbon dioxide is a greenhouse gas. The more of it added to the atmosphere, the warmer the planet gets.
* Humans have been adding it rapidly since the industrial revolution began, and more rapidly during the past fifty years.
* Scientists have measured a woldwide increase in average temperature over those fifty years, and have documented many effects of the observed rise in temperature.
* One such effect is more water vapor in the atmosphere. Water vapor is another greenhouse gas, and so it augments the warming.
* If present trends continue, it is very likely that human civilization will run into severe problems.
So much is settled science, and Dr. Koonin agrees with it all in his essay. What he doesn't agree with is that science can predict the future. But science does not claim to do that. One reason it does not is that human actions can change. Hypothetically, we might all stop using private cars. Governments might pay for all buildings to be well-insulated. Someone might invent a workable nuclear fusion power plant, making fossil-fuel power obsolete. This list could go on and on.
Science can and does make projections of future conditions. You can do that yourself, and you don't need computer models to do it. Only take the known temperature rise, assume it's linear over time, and project it on a sheet of graph paper for the next 100 years. Do the same for the pH level in the oceans. Despite what Dr. Koonin implies, there's general agreement that both trends portend risks for humanity. That, in turn, suggests that a general policy of reducing CO2 emissions is warranted. It says nothing about how the reduction is to be achieved; that is for the policymakers.
Unfortunately, policymakers — especially in the U.S. — have dropped the ball. No; they've grabbed it and punted it into the stands. They've left a policy vacuum, and Dr, Koonin's piece contributes to that. I don't claim to know his motives for writing it. But it's clear that many policymakers in Washington are motivated to preserve the status quo, and that there's some serious money behind that. You don't need to posit a conspiracy; you just need lots of people acting out of short-sighted self-interest.
Don't you be one of them.
Well put, both #19 & #20.
"John will likely run to yet another meme"
"The truth is that the data has been doctored and continue to do it. People have admitted it. Nasa was only 38% sure it was the warmest year when those article were published."
Not quite a new meme, but rather a repetition from an earlier unsubstantiated claim, where John, upon request for evidence, came with the Koonin article, which did not support his claim.
Sigh. We really need a better class of denialists. This one already starts to recycle his unsubstantiated claims after a single round...
This model comes with a pull-string in its back, and a mechanical player. I think the newer models are electronic and can recycle a wider range of delusional claims (some with the ability to substitute names and specific values).
Here's the article showing no slow down from NASA
Here’s the article showing no slow down from NASA
... five years and one day ago.
Geddy please see the update and link therein above to clarify the relationship between the NASA research and the research presented here.
And (apparently) under-appreciated aspect of Rahmstorf et al is the time scale of the study. The NASA study is not wrong, it is simply of an insufficient time scale.
If only John would do his homework. The Koch brothers' strategy for protecting their fossil-fuel assets is a matter of public record. It can't really be called a "conspiracy" because it's all perfectly legal, and it's not a secret.
For example, John could view the IRS form 990s of 89 public policy-related "nonprofit" organizations, all focussed on “educating the public and lawmakers about energy, the environment and other issues", that received $41.2 million from Koch family foundations between 2007 and 2011.
One presumes John would be "skeptical" of findings by the American University School of Communication, but how about Forbes ("Capitalist Tool")? In 2012 the magazine published "Inside The Koch Empire: How The Brothers Plan To Reshape America". Excerpt:
I have little doubt that Charles Koch sincerely supports property rights, educational choice and economic freedom. After all, he made much of his private fortune by socializing the climate-change costs of his business. The more "economic freedom" he enjoys, the higher his profits will be. Why wouldn't Mr. Koch invest a few $100 million of his person $41.8 billion to keep the cost of AGW external to the price of oil? Does John think Koch is a fool?
really should read
Out of the score of people I've talked with who identified themselves as libertarians, not even one of them knew what a libertarian is, nor knew what libertarianism is.
Probably because political anarchy begets intellectual anarchy.
...or is that the other way around??