RealClimate logo


What’s going on in the North Atlantic?

Filed under: — stefan @ 23 March 2015

The North Atlantic between Newfoundland and Ireland is practically the only region of the world that has defied global warming and even cooled. Last winter there even was the coldest on record – while globally it was the hottest on record. Our recent study (Rahmstorf et al. 2015) attributes this to a weakening of the Gulf Stream System, which is apparently unique in the last thousand years.

The whole world is warming. The whole world? No! A region in the subpolar Atlantic has cooled over the past century – unique in the world for an area with reasonable data coverage (Fig. 1). So what’s so special about this region between Newfoundland and Ireland?

Rahmstorf_2015_1rc

Fig. 1 Linear temperature trend from 1900 to 2013. The cooling in the subpolar North Atlantic is remarkable and well documented by numerous measurements – unlike the cold spot in central Africa, which on closer inspection apparently is an artifact of incomplete and inhomogeneous weather station data.

It happens to be just that area for which climate models predict a cooling when the Gulf Stream System weakens (experts speak of the Atlantic meridional overturning circulation or AMOC, as part of the global thermohaline circulation). That this might happen as a result of global warming is discussed in the scientific community since the 1980s – since Wally Broecker’s classical Nature article “Unpleasant surprises in the greenhouse?” Meanwhile evidence is mounting that the long-feared circulation decline is already well underway.

The Atlantic circulation (AMOC) as part of the global overturning circulation of the oceans in an animation from NASA.

Difficult to measure

Climate models have long predicted such a slowdown – both the current 5th and the previous 4th IPCC report call a slowdown in this century “very likely”, which means at least 90% probability. When emissions continue unabated (RCP8.5 scenario), the IPCC expects 12% to 54% decline by 2100 (see also the current probabilistic projections of Schleussner et al. 2014). But the actual past evolution of the flow is difficult to reconstruct owing to the scarcity of direct measurements. Therefore, in our study we use data on sea surface temperatures in order to infer the strength of the flow: we use the temperature difference between the region most strongly influenced by the AMOC and the rest of the northern hemisphere.

Atlantic Conveyor rc

Fig. 2 Schematic of the Atlantic circulation. Surface currents in red, deep currents in blue, sea-ice cover in winter in white. (Source: Rahmstorf, Nature 1997)

Now we are not the first to have inferred from temperature data that the flow must have weakened.  Evidence for this was already presented by Dima and Lohmann 2010 or Drijfhout et al. 2012, among others (for further references see the introduction of our paper).

What is new is that we have used proxy reconstructions of large-scale surface temperature (Mann et al, 2009) previously published by one of us (study co-author and RealClimate co-founder Mike Mann) that extend back to 900 AD (see “What we can learn from studying the last millennium (or so)”) to estimate the circulation (AMOC) intensity over the entire last 1100 years (Fig. 3). This shows that despite the substantial uncertainties in the proxy reconstruction, the weakness of the flow after 1975 is unique in more than a thousand years, with at least 99 per cent probability. This strongly suggests that the weak overturning is not due to natural variability but rather a result of global warming.

Rahmstorf_2015_3brc

Fig. 3 Time series of the temperature difference between the subpolar North Atlantic and the entire northern hemisphere, which can be interpreted as an indicator of the strength of the Atlantic circulation.

Also in 2014 we again find a remarkable cold bubble over the northern Atlantic – as a look at the NASA website shows. 2014 was globally the warmest year on record, 1 °C warmer than the average for 1880-1920. But the subpolar Atlantic was 1-2 °C colder than that baseline. And even more recently, NOAA last week released the stunning temperature analysis for the past winter shown in Fig. 4. That winter was globally the warmest since records began in 1880. But in the subpolar North Atlantic, it was the coldest on record! That suggests the decline of the circulation has progressed even further now than we documented in the paper.Winter15NOAA

Fig. 4 Temperature anomaly map for the past december-january-february, from NOAA.

The role of Greenland

Another new aspect is the importance of the increasing mass loss of the Greenland ice sheet, which causes extra freshwater to enter the North Atlantic that dilutes the sea water. We have joined forces with the Greenland expert Jason Box who has reconstructed the mass balance of the Greenland ice sheet since 1840 (Fig. 6 of our paper, see also his blog). The ice loss amounts to a freshwater volume which should have made an important contribution to the observed decrease in salinity in the northern Atlantic – probably including the “great salinity anomaly” of the 1970s, famous amongst oceanographers.

Greenland09-59

Meltwater on the Greenland ice sheet. Photo: Ian Joughin.

What are the impacts of a slowdown?

The consequences of a large reduction in ocean overturning would look nothing like the Hollywood film The Day After Tomorrow. But they would not be harmless either – e.g. for sea level (Levermann et al. 2005) particularly along the US east coast (Yin et al. 2009), marine ecosystems, fisheries and possibly even storminess in Europe (Woollings et al. 2012). We have studied these consequences some years ago in an interdisciplinary project with colleagues from Bremerhaven, Hamburg and Norway – the results are summarized in Kuhlbrodt et al. 2009.

If our analysis is correct, then this indicates that climate models underestimate the weakening of the Atlantic circulation in response to global warming – probably because the flow in these models is too stable (see Hofmann and Rahmstorf 2009). Although these models predict a significant weakening for the future, they do not suggest this as early as the observations show it (see Fig. 2 of our paper). That the real flow may be more unstable than previously thought would be bad news for the future.

If the circulation weakens too much it can even completely break down – the AMOC has a well-known “tipping point” (Lenton et al., 2008). The latest IPCC report (just like the previous one) estimates a probability of up to 10% that this could happen as early as this century. However, this assessment is based on models that may underestimate the risk, as mentioned above. Expert surveys indicate that many researchers assess the risk higher than the (generally conservative) IPCC, as is the case for sea level. In a detailed survey (Kriegler et al 2009), the 16 experts interviewed saw already at moderate global warming (2-4 °C) a probability of a ‘tipping’ (major reorganisation) of the flow between 5 and 40 percent. With strong global warming (4-8 °C) this probability was even estimated as between 20 and 65 percent.

GFS-025deg_NH-SAT1_SST_anom20March2015

 

Fig. 5 Sea surface temperature anomaly on 20 March 2015. Note that this is relative to a baseline 1979-2000, which is already a cold period in the subpolar Atlantic. Source: Climate Reanalyzer.

 

Links

Thermohaline Ocean Circulation (Encyclopedia of Quaternary Sciences)

The Washington Post on our paper

And The Independent

Vox includes comments by some colleagues: Tom Delworth and Gerald Meehl

Peter Sinclair has posted a short video on our paper with interview clips with Mike Mann, Jason Box and myself

Climate Central weighs in with more comments from other scientists on our paper

And here a brand new paper on the impacts of an AMOC shutdown (hat tip to our reader Yvan Dutil)

By coincidence, this came out the same day as our paper: Ten years of ocean monitoring uncovers secrets of changing UK winters

 

References

Rahmstorf, S., Box, J., Feulner, G., Mann, M., Robinson, A., Rutherford, S., Schaffernicht, E. (2015): Exceptional twentieth-Century slowdown in Atlantic Ocean overturning circulation. Nature Climate Change (online)

W.S. Broecker, “Unpleasant surprises in the greenhouse?”, Nature, vol. 328, pp. 123-126, 1987. http://dx.doi.org/10.1038/328123a0

C. Schleussner, A. Levermann, and M. Meinshausen, “Probabilistic projections of the Atlantic overturning”, Climatic Change, vol. 127, pp. 579-586, 2014. http://dx.doi.org/10.1007/s10584-014-1265-2

M. Dima, and G. Lohmann, “Evidence for Two Distinct Modes of Large-Scale Ocean Circulation Changes over the Last Century”, Journal of Climate, vol. 23, pp. 5-16, 2010. http://dx.doi.org/10.1175/2009jcli2867.1

S. Drijfhout, G.J. van Oldenborgh, and A. Cimatoribus, “Is a Decline of AMOC Causing the Warming Hole above the North Atlantic in Observed and Modeled Warming Patterns?”, Journal of Climate, vol. 25, pp. 8373-8379, 2012. http://dx.doi.org/10.1175/jcli-d-12-00490.1

M.E. Mann, Z. Zhang, S. Rutherford, R.S. Bradley, M.K. Hughes, D. Shindell, C. Ammann, G. Faluvegi, F. Ni, Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly, Science, 326, 1256-1260, 2009. http://dx.doi.org/10.1126/science.1177303

A. Levermann, A. Griesel, M. Hofmann, M. Montoya, and S. Rahmstorf, “Dynamic sea level changes following changes in the thermohaline circulation”, Clim Dyn, vol. 24, pp. 347-354, 2005. http://dx.doi.org/10.1007/s00382-004-0505-y

J. Yin, M.E. Schlesinger, and R.J. Stouffer, “Model projections of rapid sea-level rise on the northeast coast of the United States”, Nature Geosci, vol. 2, pp. 262-266, 2009. http://dx.doi.org/10.1038/ngeo462

T. Woollings, J.M. Gregory, J.G. Pinto, M. Reyers, and D.J. Brayshaw, “Response of the North Atlantic storm track to climate change shaped by ocean–atmosphere coupling”, Nature Geosci, vol. 5, pp. 313-317, 2012. http://dx.doi.org/10.1038/NGEO1438

T. Kuhlbrodt, S. Rahmstorf, K. Zickfeld, F.B. Vikebø, S. Sundby, M. Hofmann, P.M. Link, A. Bondeau, W. Cramer, and C. Jaeger, “An Integrated Assessment of changes in the thermohaline circulation”, Climatic Change, vol. 96, pp. 489-537, 2009. http://dx.doi.org/10.1007/s10584-009-9561-y

M. Hofmann, and S. Rahmstorf, “On the stability of the Atlantic meridional overturning circulation”, Proceedings of the National Academy of Sciences, vol. 106, pp. 20584-20589, 2009. http://dx.doi.org/10.1073/pnas.0909146106

T.M. Lenton, H. Held, E. Kriegler, J.W. Hall, W. Lucht, S. Rahmstorf, and H.J. Schellnhuber, “Tipping elements in the Earth’s climate system”, Proceedings of the National Academy of Sciences, vol. 105, pp. 1786-1793, 2008. http://dx.doi.org/10.1073/pnas.0705414105

E. Kriegler, J.W. Hall, H. Held, R. Dawson, and H.J. Schellnhuber, “Imprecise probability assessment of tipping points in the climate system”, Proceedings of the National Academy of Sciences, vol. 106, pp. 5041-5046, 2009. http://dx.doi.org/10.1073/pnas.0809117106

119 Responses to “What’s going on in the North Atlantic?”

  1. 51
    Killian says:

    #19 Hank Roberts said, Wili, we know we’re f*ed.
    The devil is in the details — to know those, we need good science for choosing to work toward the _right_ changes.

    This is incorrect in the current circumstances. If all climate science stopped tomorrow it would not affect what we need to do. This isn’t a typical Current Paradigm situation, this is unique in human history.

    It’s almost as simple as,

    “Doc, it hurts when I do this.”

    “Then don’t do that!”

    There is one result that can fix this: Cooling the planet. There is only one broad approach to doing that: Stop using stuff.

    Simplify. We need not one iota more of science in any field to do this. We are well past paralysis by analysis. The problem is helping people understand this.

    By all means, continue with the climate science, but the need for it lies not in solutions, but in if we fail to act. It will be nice to know where to go to allow the largest number of generations to survive, and survive as well as possible.

  2. 52
    Killian says:

    #41 Barton Paul Levenson LK, “Capitalism” is not the problem, or else the Soviet Union wouldn’t have wreaked so much environmental destruction, and the Communist Peoples’ Republic of China wouldn’t be the world’s largest emitter of CO2.

    False logic. There is nothing about Communism as practiced in Russia or China that would inherently constrain growth – particularly since neither were nor are actual communism.

    Both function just like capitalism in the consumption of resources and creation of a super-wealthy class.

    It is consumption that drives environmental destruction more than anything. So, if you want to be picky, call it growth, but I see no real distinction between Western Capitalism and Eastern Capitalism, er, communism, particularly now. In fact, I think it can be very successfully argued the “success” of Western Capitalism that forced Eastern Capitalism, er, communism, to turn to…. capitalism.

    “Human irresponsibility and inability to think long-term is the problem.”

    Also false. Humans can and do. Most humans don’t do this well, but not all. This is an important distinction, as opposed to hair splitting, because it means there are model societies out there to borrow patterns from.

  3. 53
    Hank Roberts says:

    > there are model societies out there

    That’s one thing science fiction offers us, too.
    And that’s why I mentioned Kim Stanley Robinson.
    He suggests a way to cope with a thermohaline failure.
    No spoiler. If you’ve read it you know what he suggested.

    Dunno if it’d work.
    Haven’t seen any other ideas.

  4. 54

    This winter we had a strongly positive NAO. There was effectively a vortex around Greenland bringing cold air and cold fresh water down from the northwest in the Labrador sea. Southwesterly winds drove the Norwegian current faster than normal towards the Arctic. The SST pattern this winter is reflective of the positive NAO and AO. The cold SSTs were the result of the northwest winds down the Labrador sea and the intense cold air outbreaks this weather pattern brought over the north Atlantic, not weak overturning.

    I would like to see Tal Ezer’s paper. His other reports have been consistent with Florida current cable measurements of Gulf Stream transport and satellite altimetry. However, I’m not sure this report is based on the non-technical write up. Changes in winds and increases cold air advection could explain some cold temperature patterns in the north Atlantic.

    The popular write up on this report has conflated the Gulf Stream intensity with deep convective overturning. I’m not sure people here are discussing the same processes and data sets.

    [Response: There is some arguments against a local wind response in the North Atlantic. E.g. the warming in the South Atlantic especially the Benguela Current region, another characteristic of an AMOC decline. And the sudden drop in hemispheric temperature difference analysed by Thompson et al (cited in our paper) that coincided with the 1970s cooling – this also points to an AMOC decline, since the AMOC is the reason why the Northern Hemisphere is warmer than the SH in the first place. Also, in models you find that subpolar cooling in the North Atlantic strongly correlates with the AMOC, and the models do predict an AMOC decline and the associated cooling in that area in response to global warming – just not quite as early as we see it in the data. – stefan]

  5. 55
    patrick says:

    Stefan, thanks for the post and documentation. Thanks for leadership and clarity. Thanks, Jason Box. Thanks Mike Mann and all co-authors.

    Graphic artist, videographer, editor Peter Sinclair: if you rose to this occasion so well (“A Nasty Surprise…”), it’s only because you are so well practiced. I’d quote the end and mention multiple ironies there (after all that debunking along the way) but I wouldn’t want to spoil it.

    https://www.youtube.com/watch?v=L-bXLPLCyek#t=15

    http://erb.umich.edu/blog/2013/08/06/details-communicating-climate-science-in-the-disinformation-era/

    https://www.youtube.com/watch?v=XZGsdnYqbjk

  6. 56

    BPL: Human irresponsibility and inability to think long-term is the problem.

    K: Also false. Humans can and do. Most humans don’t do this well, but not all. This is an important distinction, as opposed to hair splitting, because it means there are model societies out there to borrow patterns from.

    BPL: Oh, please list the model societies humans have created, K.

    This should be good.

  7. 57
    Lawrence Coleman says:

    Very very interesting article! Just been comparing from where that cool pond extends to and from(from 40*N 40*W all the way to 60*N 15*W) that is a significant portion of the warm surface current of the AMOC that flows through the cool pond. Probably will make coming winters in northern Europe and East-Coast America very chilly indeed.
    The summers I believe will still be dominated by the slowing jet stream and rossby like excursions and blocking waves from the equator will I think win against relative cooling effects of so much Greenland fresh melt water flooding the north surface waters, so prolonged heatwave periods and even warmer nights for those in the north Atlantic I think I can see. Nutshell _ extremes getting ever more pronounced in winter and summer.

  8. 58
    Yvan Dutil says:

    I have found this paper about the consequence of the collapse of AMOC. Pretty scary! No the Day after Tomorow scenario but not far from it either!

    Jacsjon et al, Global and European climate impacts of a slowdown of the AMOC in a high resolution GCM

    http://link.springer.com/article/10.1007/s00382-015-2540-2

    [Response: Thanks! Had not seen this new paper yet! -stefan]

  9. 59
    CM says:

    [OP]: The whole world is warming. The whole world? No! A region in the subpolar Atlantic has cooled (…) what’s so special about this region between Newfoundland and Ireland?

    It’s inhabited by indomitable Gauls? :-) Appreciate the reference.

    [Response: Glad somebody noticed! -stefan]

  10. 60
    wili says:

    BPL, I don’t know about ‘model societies.’ By definition, there are no utopias. But there are a (very few) moments in the history of civilization where people with power chose to consciously simplify their society in order to give it a better chance of survival going forward. (Usually, though, we respond to the problems that complexity creates with ever more complexity.)

    Joseph Tainter is asked just this question at about 1:14–https://www.youtube.com/watch?v=G0R09YzyuCI

  11. 61
    Jeff says:

    Steven,

    I noticed that your paper does not reference “On the long-term stability of Gulf Stream transport based on 20 years of direct measurements” by Rossby et al. Here is a link:
    http://onlinelibrary.wiley.com/doi/10.1002/2013GL058636/abstract

    Is that because you do not consider it relevant to your discussion, or that you consider it to be a flawed paper, or ???

    Sincerely,

    Jeff

    [Response: Not flawed at all – see my response to #30. -stefan]

  12. 62
    Racetrack Playa says:

    For those interested in the details of the scientific controversy regarding a North Atlantic-based driver of global climate change (via modulation of the AMOC) and a tropics-based (i.e. 30N-30S) driver of global climate change (via modulation of equator-to-pole heat transport rates and variations in overall radiative forcing), a good place to start is Carl Wunsch’s 2002 article titled “What is the thermohaline circulation”:

    http://www.esrl.noaa.gov/psd/people/dezheng.sun/lectures/haline/wunsch_sci_2002.pdf

    So, one point is this:
    “If the flow is integrated zonally in the ocean (see the figure), one notices what is best called a meridional overturning circulation (MOC) (3). Features such as the Gulf Stream are not evident, but the Gulf Stream dominates the mass flux in the upper ocean and is clearly part of the MOC (1).” (Wunsch)

    vs.

    “We are talking about the AMOC here, not the western boundary current [Gulf Stream] which indeed is largely wind-driven, and more specifically about the thermohaline driven part of the AMOC.” – (stefan)

    Another, popular science take on the issue is Mark Bowen’s “Thin Ice” about the work of Lonnie Thompson on tropical ice cores retrieved from mountaintops in the region, which clearly lays out the nature of the scientific controversy – and apparently quite a bit of bad feeling between the different scientific groups, nasty fights over access to funding, and so on. This is not uncommon in science, of course.

    One possibility is that both groups are right to some extent, in that background conditions (the extent of polar ice sheets) play a central role, but this is a very contentious issue in climate science circles, similar in scope to the controversy over projections of ice melt rates and sea level rise in the 1990s – some people had argued that melt rates would be much lower than observed, and it turned out what they had missed were how the dynamics of ice sheet movement would play into melt rates.

    My own take is that variability in global winds is a far more important control over global climate than thermohaline circulation, however it is defined, because the global wind field –

    “. . . not only shifts the near-surface wind-driven components of the mass flux, but also changes the turbulence at depth; this turbulence appears to control the deep stratification.” – Wunsch

    Hence the Pacific wind theory behind the hiatus in global warming seems to be a robust argument:

    Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus, (England et al Nature Climate Change 4, 222–227 (2014)

    http://www.nature.com/nclimate/journal/v4/n3/full/nclimate2106.html

  13. 63
    wili says:

    Jeff, your question was already answered above under #30.

  14. 64
    sidd says:

    Please can we confine this thread to AMOC slowdown and take the discussion of sustainability or lack thereof to a more appropriate thread, say the borehole, or failing that, the Unforced Variations thread ?

    I have a question about AMOC slowdown: Does not the AMOC represent heat export from the Southern to the Northern Hemisphere, and as such, should we expect increased warming in the former in the event of sustained AMOC slowdown ? If so, over would the timescale be comparable to deep ocean mixing or faster, given that we already see some reduction of AABW formation and warming signal at depth in the Southern ocean ?

    sidd

    [Response: In our paper we note that the greatest ocean warming of the Southern Hemisphere is indeed found in the South Atlantic, especially around the Benguela Current region. In models, a warming in that area is a highly characteristic response to an AMOC slowdown, due to the reduced northward flow there. -stefan]

  15. 65
    Jim Eaton says:

    Hank Roberts (at #33). It was interesting to see your comments on Kim Stanley Robinson’s trilogy on global warming. Stan is a neighbor and friend, but I haven’t had chance to speak with him about the latest science on climate change. For those of you not familiar with his books (Red Mars and Antarctica being perhaps his best known), Stan is an award winning science fiction writer who is very heavy on science in his writings. The only difference I have with him is that Stan is an eternal optimist about solving the climate change crisis while my geologic background leads me to be a pessimist.

  16. 66
    Jeff says:

    To Stefan (#61) and Wili (#63),

    Thank you for your responses. The paper I referenced was brought to my attention by a colleague who is adamantly on the other side of the issue (his resources include the sites WUWT, Roy Spencer, and Judith Curry). He was certain that this site would delete my question, and I was equally certain that no such thing would occur – it has cost him $10.

    I think the issue we are seeing with the controversy over AGW is that the internet provides support for any bias one might have; unfortunately, the vast majority of people (including myself) do not have the skill set to separate the wheat from the chaff wrt specific areas of scientific knowledge outside of individual areas of expertise. But many people simply don’t realize how shallow is their knowledge.

    However, one can gain a sense of scientific integrity by observing the comments/discussion which occur within the various websites. After having read several comment threads at Dr. Curry’s site I am certain that the level of integrity at sites such as RealClimate, andthentheresphysics, skepticalscience is much greater than at sites like Dr. Curry’s, WUWT, etc.

    Thank you for demonstrating that fact (bias) one more time!

    Sincerely,

    Jeff

  17. 67
    Slioch says:

    I am unclear as to the relative contributions to the “remarkable cold bubble over the northern Atlantic”, ie the low temperature anomaly, from what appear to be two possible causes:

    1. a slowdown in AMOC, and
    2. release of ice-cold melt-water from Greenland.

    Is it the case that it is considered that the cold anomaly is entirely due to 1., and, if so, why is a contribution from 2. ruled out?

    [Response: You can do a quick back-of-envelope: warming about 100 km3 meltwater per year from 0 °C to 8 °C (a typical mean sea surface temperature in that region) requires a heat input of about 1011Watt. The AMOC heat transport is about 1015Watt. This means that a 10% weakening of the AMOC has a 1,000 times larger effect on the heat budget of the region than the addition of cold meltwater from Greenland. -stefan]

  18. 68
    Christopher Yaun says:

    NOAA tide charts show a sharp rise in sea level along east coast during 2009, 10 and 11.

    Portland Me recorded 7 inches. Boston harbor records 9 inches.

    Are the two phenomenon connected?

  19. 69
    wili says:

    Slioch @#67, my understanding is that your #2 is at least partly responsible for your #1.
    Christopher @68, probably a slowdown or even a shift in position in the AMOC is the only thing that could raise local sea level that fast, as far as my limited understanding goes.

    Thanks to Hank and Jim for the recommendation of the KSR trilogy–definitely worth looking into.

  20. 70
  21. 71
    Tom says:

    66 Jeff says: I think the issue we are seeing with the controversy over AGW is that the internet provides support for any bias one might have; unfortunately, the vast majority of people (including myself) do not have the skill set to separate the wheat from the chaff wrt specific areas of scientific knowledge outside of individual areas of expertise. But many people simply don’t realize how shallow is their knowledge.

    Jeff,

    I am a technical profetional with no real climate knowledge other than what I have gleaned from this site and others. I think of myself as intelligent and resourceful with a good general background in the sciences. So I was surprised how easily I became confused at first by the plethora of disinformation out there. But it may not be as difficult as you think to help others find the truth if they are interested in finding it. Here are some things that helped me.

    1. I found a lot of logical inconsistencies in the denialist world. They embraced the fact that the warming we were seeing was a good thing, at the same time as they were saying that it was too slow to make a difference, at the same time as saying it was not really happening, at the same time as saying we really were not sure weather it was or was not happening, at the same time as saying it really was happening but we had no idea why, etc. In other words, no one really seemed to be interested in finding out what was really going as much as they were in accepting just about anything that denied what most climate scientists were saying. That sort of disingenuous treatment of the scientific method should not sit well with anyone that has a true interest in science, or the truth.

    2. A lot of the denialist side does not have much real data and references to back them up, and none of them seem to be doing primary research. There is no one at the Heartland institute that travels to Greenland to dig up ice cores, or measure tree rings. The people who are really close to the data never seem to be in the denialist camp. Those few denialist articles that look official and have references, will point to data collected by others, and when you go to the source they reference you see that the people who actually collected the data have a very different view of what is happening and what the data shows us. In some cases they are actually outraged that there data is being misrepresented, incompletely represented, or in some cased misrepresented.

    3. There are several denialist talking points that seem clearly intended to deceive. When someone says there has been no warming since a particular year, that just jumps out to me as cherry picking and makes me want to see some long term plots and make sure there was nothing unusual about that particular year. Someone that is too ready to take advantage of an anomaly for the sake of argument is not really interested in finding the truth are they?

    4. But perhaps the one thing that anyone who is not scientifically literate SHOULD be taking into account is the sheer number of scientific organizations who recognize and support the prevailing tenants of climate science. I have literally lost track of the number of organization I know and respect that say that climate change is real, it is man made, and we need to be very concerned about the effects. Given the amount of data and scientific consensus on this side, any opposing view would need to cross some very high thresholds to be on the same level. Someone who uses one cold winter in their locality or some other trivial bit of data to justify challenging this level of knowledge and research is hardly a denier, or a skeptic, they are perhaps better described as a crackpot.

    Just my opinion as a knowledgeable person untrained in climate science. Your mileage may vary.

  22. 72
    sidd says:

    Thank you for the reply, Prof. Rahmstorf. I seem to have missed the part of your paper that referred to warming of the Benguela current. In penance, I quote:

    “The observational data show a clear dipole response in the Atlantic, with the North Atlantic cooling and the South Atlantic warming when comparing 1961–1980 with 1941–1960. The maximum of South Atlantic warming is within the Benguela Current off southern Africa and the maximum of North Atlantic cooling is found within the Gulf Stream. These patterns are highly characteristic of AMOC changes and are found in many model simulations wherein the AMOC is weakened by freshwater ‘hosing experiments’. The Atlantic see-saw pattern is also evident in Fig. 1, where out of all Southern Hemisphere ocean regions the South Atlantic has warmed the most.”

    I used to think that the warming of the Benguela current was due to increased eddy leakage out of the Agulhas current around the Cape of Good Hope bringing warm Indian Ocean water into the Atlantic, and was not previously aware of the warming signal there seen in hosing experiments. Upon examining Figure 1. in the light of the last sentence in the quote above, I notice that regions further south than the Benguela also show pronounced warming: are these also seen in hosing experiments?

  23. 73
    sidd says:

    A follow up question: IN hosing experiments is there any response seen at depth in the southern ocean ? In particular, is there any warming and/or freshening seen at depth in the Southern Ocean in response to freshwater injection ito the N. Atlantic ?

    sidd

  24. 74
  25. 75
    Dp says:

    Researching this online I came across a paper by Richard Seager of Columbia university. He said that the gulf Stream only has a marginal effect on the temperatures of North West Europe. He puts it down to the atmosphere. basically oceans absorbs heat in the Summer and releases it in the Winter. Therefore anywhere down wind of the oceans is going to have a mild climate. Is anybody familiar with this?

    [Response: There were some logical flaws in Seager’s arguments, which I also saw right away when reading the paper back then and which were immediately responded to by Rhines and Häkkinen here: https://usclivar.org/sites/default/files/amoc/Rhines_Hakkinen_2003.pdf -stefan]

  26. 76
    Killian says:

    Dear Moderator: Allowing this soirt of garbage, but not the responses, does not reflect well on this site. The favoritism is not something anyone respects…. except the favorites, of course, who run around this site like schoolyard bullies…. with the teacher’s tacit approval.

    BPL: Human irresponsibility and inability to think long-term is the problem.

    K: Also false. Humans can and do. Most humans don’t do this well, but not all. This is an important distinction, as opposed to hair splitting, because it means there are model societies out there to borrow patterns from.

    BPL: Oh, please list the model societies humans have created, K.

    This should be good.

    Comment by Barton Paul Levenson — 25 Mar 2015 @ 6:24 AM

    Weasel words/Straw Men/sarcasm italicized.

  27. 77

    #69–wili, I don’t know about ‘the only thing’, but at least two papers suggest it *is* the thing:

    http://www.geos.arizona.edu/sites/www.geo.arizona.edu/files/pictures/Yin_Oceanic%20control.pdf
    http://www.nature.com/ncomms/2015/150224/ncomms7346/abs/ncomms7346.html

    #71–Tom–Yes. Point #1 is summarized musically thus:

    https://soundcloud.com/doc-snow/laughing-fool-blues

  28. 78
    Thomas O'Reilly says:

    #38 Concerned Teen & #18 Chuck Hughes (and respondees) and CO2e 1000ppm

    Dr Peter Ward, highly qualified paleontologist summarizes the issues nicely in this video excerpt. specifically the ocean currents and what comes next based on the accumulated SCIENTIFIC KNOWLEDGE of the past and present.
    https://www.youtube.com/watch?v=HP_Fvs48hb4&feature=youtu.be&t=33m1s

    The question might be “when” will 1000ppm be a reality.

    To calculate that one needs to go looking for themselves, because the IPCC consensus system is always extremely conservative and the less scary, and of course based on “assumptions” that rarely stack up. All the most important “IPCC forecasts” have all been beaten by decades already .. there is a pattern, telling everyone to disregard the IPCC projections and look into the details.

    The projections of renewable non-carbon energy uptake are also BS and extremely overstated. Lot’s of theories little reality.

    COP21 in Paris is already doomed to fail – no nation or group of nations with power, are politically ready to do what is necessary to stop and reverse the Global warming drivers.

    Business as Usual (BAU) conditions prevail, despite many one-off good news stories. Meaning Business as usual accepts additional uptake of non-carbon energy use at massive uptake levels into the future… but does not neglect the FACT that Carbon energy uptake in REAL TERMS increases even faster from here on in too!

    Tipping Points one after another are now the norm – zero summer arctic sea ice any day after 2020 is the example reality here.

    The issue is no longer climate science or the IPCC or minutia issues or which ‘science guru” is “more right” academically.

    Absent the outlier theories +/-, and BAU means an atmospheric CO2e of 960 PPM by 2100.

    It could be sooner, it could be later. But when is, in fact, IRRELEVANT –

    That’s only my opinion. Of course others will disagree. And of course others will discount out of hand a 960 PPM figure for 2100. That isn’t my problem, that is theirs. I have nothing to prove – the evidence is already out there – everywhere!

    The malignant narcissists, the sociopaths, the insane influence and rule the world, and therein lies the “Hardest of Problem” to fix.

    And as many say — “We’re Fcuked!” —

    [Response: You cannot give a certain atmospheric CO2 ppm limit for an AMOC shutdown, because this risk very much also depends on the speed at which you ramp up atmospheric CO2 and temperature – the faster you do it, the more it affects the AMOC. There are practically no paleo analogues of the fast global warming experiment we are conducting now. -stefan]

  29. 79
    Thomas O'Reilly says:

    The UN’s climate science body has NOT previously included the ice sheets of Antarctica and Greenland in its PREDICTIONS for future sea level rise because scientists are NOT CERTAIN (?) how fast they will slide into the ocean.

    Holland said: “What humanity needs to know is what’s the sea level rise in 2100 and the biggest source of uncertainty in that is what’s going to happen to the ice sheets.”

    Published Online March 26 2015
    Volume loss from Antarctic ice shelves is accelerating
    Fernando S. Paolo1,*, Helen A. Fricker1, Laurie Padman2
    http://www.sciencemag.org/content/early/2015/03/25/science.aaa0940

    Correction back to what is really the ONLY thing that is important:
    What humanity needs to know is how to reverse AGW/CC Drivers now – and then do it.

  30. 80
    Steve Fish says:

    Re- Comment by Killian — 26 Mar 2015 @ 4:41 PM, ~#75

    Your comments are way off topic. Why don’t you just post the answer to BPL in the Unforced Variations thread? I also would like to know the answer to his question and the fact that it is sarcastic, but not weasely or a straw man is telling. Just answer the question.

    Steve

  31. 81

    Thanks Stefan for further elucidating on your study here. In writing my own article about your study I came across Pérez et al (2013) in Nature Geoscience: Atlantic Ocean CO2 uptake reduced by weakening of the meridional overturning circulation. This paper argues that a slow down of the AMOC results in a reduction of efficiency in the sub-polar Atlantic ocean carbon sink. This observational impact since 1990 doesn’t seem to be mentioned in your paper or in discussion of impacts of the rapid slowing of AMOC. If the Atlantic Ocean carbon sink reduces in efficiency, then surely more CO2 will accumulate in the atmosphere boosting warming from the greenhouse effect. Here is the link to the study:
    http://www.nature.com/ngeo/journal/v6/n2/full/ngeo1680.html

    How relevant is this effect and has this impact been considered in climate models?

    [Response: Indeed this has been a concern since the 1990s, see e.g. Sarmiento et al. (Nature 1998) which we discuss in the Kuhlbrodt et al. paper on impacts that is mentioned in my post. -stefan]

    My own review of your article and other recent AMOC related research:
    http://takvera.blogspot.com.au/2015/03/a-north-atlantic-nasty-surprise-amoc.html

  32. 82
    Thomas O'Reilly says:

    #75 Killian – I can see your own “hand waving” and a healthy dose of your own version of “Weasel words/Straw Men/sarcasm” and that’s all. Just sayin’ … I don’t care either way. Besides it is only an “internet discussion board” at the end of the day.

  33. 83

    I’m amused that K listed “model societies” as an example of my sarcasm and/or weasel words when it’s a direct quote from his post–as can be seen directly above where he quotes me.

    Proofread, K, proofread. That way you’re more likely to catch stuff like that.

  34. 84
    Chuck Hughes says:

    “The latest IPCC report (just like the previous one) estimates a probability of up to 10% that this could happen as early as this century. However, this assessment is based on models that may underestimate the risk, as mentioned above. Expert surveys indicate that many researchers assess the risk higher than the (generally conservative) IPCC, as is the case for sea level.”

    I don’t mean to sound disrespectful but just once, I’d like for ‘scientists’ to “over estimate” their predictions or even go with a “worst case scenario” so we’d have a more realistic idea of what to expect. Even the worst projections from the IPCC don’t measure up to reality. I’m thinking 3′ of SLR by the end of this century is a joke at this point. With Antarctica and Greenland in the mix, who knows? Certainly the movie “Day After Tomorrow” has a lot more credibility than it did. I might even go watch it now. Erring on the side of “caution” seems to be a bad method for survival in this business. I know it’s part of the scientific code of ethics but it’s not working out for the rest of us and it’s not getting our politicians off their a$$e$.

    Maybe if we started equating these figures with human mortality…

  35. 85
    15120092 says:

    How would this change in currents affect the amount of heat in the surface layer that is transported into the Arctic and contributes to melting the Arctic Sea Ice? Would this reduce the heat transported or have little affect?

  36. 86
    Slioch says:

    re. 67 Thanks Stefan.
    Gosh. I hadn’t realised the extent to which we are dealing with an ant and an elephant.

  37. 87
    Mal Adapted says:

    TOR

    And as many say — “We’re Fcuked!”

    Hmm, I haven’t actually heard anyone say that.

  38. 88
    patrick says:

    https://www.facebook.com/MichaelMannScientist/posts/873222562733947

    http://scienceblogs.com/gregladen/2015/03/23/new-research-shows-exceptional-slowdown-in-major-atlantic-ocean-currents/

    Michael E. Mann (on Facebook March 25) provides useful, helpful–if not essential–clarifications especially for anyone mildly confused about names and terminology. Plus: anyone comparing this work to that of T. Rossby et al. 2014.

    This is linked from Greg Laden’s very helpful backgrounder on Laden’s blog March 23, about this work and and this post.

  39. 89
    patrick says:

    To be clear: the link to Michael E. Mann’s Facebook post is linked by the UPDATE to the March 23 post on Greg Laden’s blog.

  40. 90
    Lawrence Coleman says:

    20: richard pauli. In an ironic way this is why climate science now has to the most fascinating branch of science on the planet. So many brand new studies are coming out every week showing more clearly a piece of the AGW machinery in finer detail. In many cases a new piece of the jigsaw altogether. What I also find astounding is that in almost every study it shows that we have been drastically underestimating the problem for many many years. Two new studies that I cam e across recently show that the amazon region is sequestering 50% less carbon than a few decades ago. It would have been helpful and indeed useful if a study had come out 20 years ago showing perhaps a 15% reduction in CO2 uptake. Then governments and industry would have had a chance to act on the problem sooner. Another study showed a 45% reduction the number of invertebrates in the past 40 years. Why wasn’t there studies done earlier showing the beginning of a decline than wait till it’s too bloody late to do anything?. Now another study showing the AMOC well on it’s way -if not grinding to a halt then at least alarmingly weakening. Only last year it was still in the speculative stage whether or not the AMOC was slowing down. Now suddenly one year later conclusive evidence that it has slowed noticeably,(that study took 10 years to compile!). Is it because studies take many years to complete and even within that time changes are happening – then please give ongoing update reports.

  41. 91
    Raymond Ford says:

    Good Day,

    OK at the current melt rate that we are seeing how much time do we have until the great conveyor
    shuts off ?

  42. 92
    wheelsoc says:

    Jeff @66: However, one can gain a sense of scientific integrity by observing the comments/discussion which occur within the various websites. After having read several comment threads at Dr. Curry’s site I am certain that the level of integrity at sites such as RealClimate, andthentheresphysics, skepticalscience is much greater than at sites like Dr. Curry’s, WUWT, etc.

    I was unfortunately linked to Anthony Watts’ crowing post about how this new paper had been “refuted” by NASA, specifically in Willis (2010). Apparently he didn’t bother to notice that this previous work was already cited in the new paper, and even that the consistency (not contradiction) of the two results was highlighted.

    When it was pointed out in the comment section that the Willis paper was from 2010, Watts dutifully amended his post to reflect that. But several commenters pointing out that Willis was cited by Rahmstorf et al. as being consistent with their own results went unnoticed, or at least no correction has been posted in the 3-4 days since his post went up.

    As usual, the vast majority of the comment thread is taken up by a chorus of voices condemning climate scientists for failing to notice that somebody else had come to a “different” result, which clearly must be evidence of widespread fraud (naturally). Totally unaware of their failure to notice the citation and lack of contradiction! Weirdly, they focused their displeasure on Mike Mann to the exclusion of just about any other author (even the principal author). It’s an illustrative display of unreasoning, unprovoked, hostile ignorance.

    I share your gratitude for the real scientists and amateur popularizers who are careful and conscientious about blogging the genuine, undistorted science. It’s a necessary antidote to the sort of tribal warfare being conducted in places like WUWT. The voice of the reality-based community needs to be heard.

  43. 93
    Hank Roberts says:

    > Isn’t holding CO2 @ 400ppm the only rational and ethical response

    Yes, “peace in our time” is all that’s needed.
    No need to worry about the details.

    Glad that’s settled.

    Now, for those of us interested in the science, would you mind?

  44. 94
    jai mitchell says:

    If the temperature anomaly was not present prior to the mid 1990’s recovery of the AMOC then the later 2010+ SST anomaly in the north atlantic is somewhat precluded as a result of AMOC slowdown.

    Is it possible that a function of the east pacific ridiculously resilient ridge blocking for 2.5 years causing drought and high sea surface temperature anomalies off of the California coast is a function of regional mid and upper tropospheric aerosol loading from china, and if this is the case then is it also possible that an increased dimming/cloud response could be funneled into this region due to a standing wave pattern (the opposite dipole of the RRR)?

    Just a thought. If the indirect cloud function is severely understated then this would be a potential contributor to the regional cold SST.

  45. 95

    Isn’t holding CO2 @ 400ppm the only rational and ethical response to AGW/CC today based on existing scientific knowledge?

    Isn’t it rather strange to be asking that when you know (or should) that practically all other participants here already agree with that premise?

    Again, why not take that point somewhere where you have an actual antagonist?

  46. 96
    Killian says:

    [edit – please stop. Discuss ideas, not people.]

  47. 97
    zebra says:

    I realize it’s probably foolish to jump into the middle of this, but let me offer a suggestion for the ‘side’ represented by Stefan’s response back at #16.

    “[Response: What is your suggestion what we should do as scientists, other than study the system to our best ability and communicate what we find? -stefan]”

    I can’t speak for Killian or O’Reilly, but I do feel some empathy with their impatience, and I think I can identify the source for me at least, so I would ask this:

    Is there any prospect that the science will achieve a degree of resolution– something between climatology and meteorology– that can communicate clearly discernable consequences, with good confidence, to the public? (And of course I mean in the next decade, not a century.)

    I’ve followed the developments for quite a while now, and there has been great progress, which has made all of us more confident (and more concerned.) But from outside, and intuitively, I don’t see the path towards that better resolution of the phenomena being studied.

    Are there perhaps people working towards this, looking beyond the existing methodology for attribution and prediction? Maybe I’ve missed a post on this; if so I apologize. But I would certainly be interested in such a report, covering the various specializations. I know it would be somewhat speculative, but at least there would be something positive to speculate about for a change.

  48. 98
  49. 99

    Not sure just what Thomas means to apply #97 toward, exactly. But under “counterproductive” I would class trying to repurpose the climate science community as full time communicators, policy makers (no disrespect here to Andrew Weaver, AR author and lead author, who is currently serving in the British Columbia legislature), or PR flaks–and also repurposing RC as pure policy forum.

    Just sayin’.

  50. 100
    Jim Baird says:

    Thomas 92 “Isn’t holding CO2 @ 400ppm the only rational and ethical response to AGW/CC today based on existing scientific knowledge?”

    Per 43 above I don’t believe it is the only way.

    The Christian Science Monitor recently reported, To stop climate change, flat CO2 emissions aren’t enough.

    They cite Thomas Peterson, NOAA, saying “There are factors other than CO2 governing surface temperature and therefore global warming. . . These include cloud cover, the amount of heat absorbed by the ocean, El Niño events and more.”

    Heat absorbed by the ocean seems to have equated to the “hiatus”.

    That process can be replicated with at least 14 terawatts of clean energy production resulting, plus the movement of virtually all of the rest of the heat the oceans are absorbing annually.

    NOAA estimated that in 2010 at about 330 terawatts.

    This is the natural analogy that comports with the 2nd law of thermodynamics. Electrolysis of sea water done this way, also removes CO2 from the atmosphere.

    I fully concur with you however, that is irrational not to be discussing and moving on solutions.


Switch to our mobile site