Two decades ago, in an interview with science journalist Richard Kerr for the journal Science, I coined the term the “Atlantic Multidecadal Oscillation” (AMO) to describe an internal oscillation in the climate system resulting from interactions between North Atlantic ocean currents and wind patterns. These interactions were thought to lead to alternating decades-long intervals of warming and cooling centered in the extra-tropical North Atlantic that play out on 40-60 year timescales (hence the name). Think of the purported AMO as a much slower relative of the El Niño/Southern Oscillation (ENSO), with a longer timescale of oscillation (multidecadal rather than interannual) and centered in a different region (the North Atlantic rather than the tropical Pacific).
Today, in a research article published in the same journal Science, my colleagues and I have provided what we consider to be the most definitive evidence yet that the AMO doesn’t actually exist.
Background
Back in the 1980s and 1990s, a number of articles pointed to a pattern of North Atlantic warming during the 1930s-1950s, subsequent cooling in the 1960s and 1970s, and warming thereafter, which seemed to resemble a natural oscillation in the climate system. I co-authored an article (Mann et al, 1995) in the Nature demonstrating the apparent persistence of these multidecadal oscillations several centuries back in time based on the analysis of paleoclimate proxy data (our analysis of similar proxy data would ultimately lead, a few years later, to the now well-known “hockey stick” curve that shows the warming of the past century to be anomalous in a long-term context).
In 2000, in an article that led to Kerr’s commentary in Science, my collaborator from the climate modeling group at the Princeton Geophysical Fluid Dynamics Laboratory (GFDL) Tom Delworth and I argued that this observational evidence for an AMO-like climate oscillation was supported by an analysis of an extended (thousand+ year long) control simulation of GFDL’s state-of-the-art (at the time) coupled ocean-atmosphere model (Delworth and Mann, 2000) (pdf). Since it was a control simulation with no external “forcing” (no greenhouse gas changes, no variations in solar output, no volcanic eruptions, etc.), any oscillation that was produced has to be internally generated. And indeed we established that this model did produce such an internal oscillation, with a multidecadal timescale, centered in the extratropical North Atlantic, tied to coupled ocean-atmosphere processes involving the ocean “conveyor belt” circulation (sometimes called the thermohaline circulation and sometimes equated with the “Gulf Stream”, though the latter in fact is a wind-driven current in mid-latitudes, while the thermohaline circulation/conveyor belt represents its extension on into the higher latitudes of the North Atlantic).
About five years later, analysis of an extended simulation of yet another climate model–the coupled ocean-atmosphere model run by the Hadley Centre within the UK Meteorological Office, yielded evidence for a similar oscillation, albeit with a longer (roughly 100 year) period, and a more global signature (Knight et al., 2005).
As I’ve stated elsewhere, at times I feel like I created a monster when I gave a name to this putative climate oscillation in 2000. The concept of the AMO has since been misapplied and misrepresented to explain away just about every climate trend under the sun, often based on flawed statistical methods that don’t properly distinguish a true climate oscillation from a time-varying trend: If you assume that all trends are a simple linear ramp, and call everything left-over an “oscillation”, then the simple fact that global warming flattened out from the 1950s through the 1970s driven by the ramp-up in cooling sulphate aerosol pollution masquerades as an apparent “oscillation” on top of a simple linear trend. We’ve published a number of articles over the years (see e.g. here, here, here, here, here, and here) demonstrating that studies that use such an approach to define the AMO end up mis-attributing to a natural “oscillation” what is actually human-caused climate change. Such analyses have been used by some to dismiss, among other things, the impact climate change is having on increasingly active and destructive Atlantic hurricane seasons, attributing the increase in recent decades to a supposed upturn in the AMO.
But if the AMO is simply an artifact of studies that misinterpret the time-varying pattern of human-caused climate change as a low-frequency oscillation, what about the studies mentioned previously that identify an internal oscillation in control simulations of climate models? It turns out that they are the exception (indeed the rare exception), rather than the rule. Decades ago there were only a handful of long control coupled model simulations and two in particular (the GFDL and UK Met Office coupled models, as noted earlier) did generate an AMO-like oscillation (though the spatial patterns, timescales, and apparent mechanisms in the two cases were different enough that one could question whether they truly represented the same thing).
Today, by contrast, there are many dozens of coupled models around the world, and the Coupled Model Intercomparison Project (CMIP) makes the ensembles of simulations widely available to other researchers. So what does an analysis of these multimodel ensembles reveal?
Analysis of Historical and Control Simulations
In an article we published a year ago, we showed that the AMO does not in general exist in current generation models. We analyzed a set of long control simulations with more than 40 different state-of-the-art climate model simulations from the CMIP5 multimodel climate archive. We used a type of “spectral analysis”, a statistical procedure that identifies whether there is evidence for truly oscillatory variability (in the form of a spectral “peak”, i.e. a spike in the plot of amplitude of variation as a function of frequency/period) at some particular timescale or narrow range of timescales. The “MTM-SVD” method identifies whether an entire spatiotemporal dataset contains an oscillatory signal (as indicated by a spectral peak that is correlated across the dataset, in this case, surface temperatures spanning the globe) that is distinct from simple background noise (i.e. random variability).
As shown below (Figure 1–left), the CMIP5 control runs show strong evidence of oscillatory behavior on 3-7 year interannual timescales associated with ENSO. The vast majority of simulations exhibit a statistically significant spectral peak within that range of periods, and even the average across all simulations crosses the 90% (“p=0.1”) significance threshold, despite the tendency for cancellation when averaging (since different models yield significant ENSO timescale peaks at different periodicities within the 3-7 year range). By contrast, the models show no evidence for a spectral peak on the 40-60 year AMO timescale (see the inset which zooms in on decadal and longer timescales). The behavior on that timescale is largely consistent with what one would expect from random data.
Yet, actual historical surface temperature data from 1850-present (see thick blue curve), in addition to showing significant interannual ENSO timescale peaks, do indeed yield a spectral peak centered at a multidecadal 40-50 year period. Do the results for the historical data, then, contradict what we find with the model simulations? As it turns out, no.
Consider a parallel analysis (Figure 1-right) of the CMIP5 historical simulations. These are simulations that have been driven with the same external factors (the human factors of rising greenhouse gas concentrations and sulphate aerosols, and natural factors such as solar output changes and volcanic eruptions) that have driven temperature changes over the historical period of 1850 to present. In this case, the models reproduce the 40-50 year multidecadal spectral peak seen in the actual observations. Indeed, the peak is seen in nearly every simulation and is significant at the 99% (“p=0.01”) level even for the average over all simulations. Clearly the multidecadal spectral peak is a very robust feature of both the historical simulations and the historical observations themselves. But it’s not indicative of an AMO.
An analysis of the simulations shows that the multidecadal peak is tied to the same pattern of 1930s-1950s warming, 1960s and 1970s, cooling and warming thereafter that is seen in the actual observations as discussed earlier. That alone raises suspicions, since if this were an internally-generated oscillation, there is no reason that the warming and cooling phases in the models would coincide in timing with those in the observations. Instead, as discussed earlier, the alternating warming and cooling is tied to the competition between steady greenhouse warming and the prominent sulphate aerosol cooling of the 1950s-1970s. The aerosol cooling is especially pronounced in the North Atlantic (particularly during summer) as noted by Mann and Emanuel (2005) helping to explain why the apparent “oscillation” is most pronounced in that region.
At this point prospects for the existence of an internal AMO climate oscillation might be starting to look rather bleak. But there is still one seemingly compelling argument left for AMO advocates: If the AMO is indeed an artifact of competing anthropogenic greenhouse gas and sulphate aerosol forcing during the historical era, then why is it that AMO signals, as noted earlier, have been detected in paleoclimate proxy data that predate the historical period? In fact, a recent critique (Müller-Plath, 2020) of our analysis of the CMIP5 control and historical simulations published in the somewhat controversial journal Frontiers rests on that very argument. Is there merit to this argument?
Analysis of Last Millennium Simulations
In our new article, my co-authors (Byron Steinman, Daniel Brouillette, Sonya Miller) and I analyzed the CMIP5 “last millennium” simulations (16 in total) that span the interval 850-1849 CE. These simulations precede the historical period and are driven by natural (primarily volcanic, solar and orbital) radiative forcing alone. Application of the same (MTM-SVD) analysis as above to the model surface temperature fields yields evidence for a multidecadal (~60 year period) AMO-like spectral peak in the majority of simulations (12 out of 16 at the 90% significance level and 11 out of 16 at the 99% significance level). The results are shown in Figure 2 where they are compared against the previously discussed “control simulation” results. The difference is striking. In the control simulations, where no forcing is applied, there is no evidence (as we’ve already seen) for a distinct multidecadal spectral peak. Yet there is robust evidence for just such a peak in the “last millennium” simulations, where natural (volcanic and solar) radiative forcing has been applied. This comparison suggests that the natural radiative forcing must be responsible for the apparent AMO-like signal.
One convenient feature about the MTM-SVD method is that it allows you to reconstruct the spatial and temporal pattern of the signal associated with a particular spectral peak. We take, for example, the individual simulation (a simulation of the NASA GISS-E2-R model) that produced the most prominent ~60 year spectral peak in Figure 2B. The spatial and temporal pattern of the corresponding signal is readily reconstructed and shown in Figure 3 below.
There are a number of revealing features in the signal pattern. The spatial pattern (Figure 3A) displays a high-amplitude response in the tropical regions that is reminiscent of the pattern of response to explosive tropical volcanism (temperatures cool the most in the tropics after an explosive tropical eruption since the more sunlight you have in the first place, the more that is reduced by a volcanic dust veil). It is notable that there is also some evidence of enhanced signal amplitude along the Gulf stream extension in the North Atlantic, suggestion some possible coupling to North Atlantic ocean dynamics. A detailed analysis of the evolving spatial pattern of the signal over a typical ~60 year cycle (see article) shows a close correspondence between the initial phase (coinciding with peak global cooling) and the pattern of response to explosive tropical eruption established in some past studies (e.g. Shindell et al, 2004).
The temporal pattern (Figure 3BC) shows that the major cooling excursions coincide with several of the largest explosive tropical eruptions of the last millennium (e.g. the 1258 CE, 1331CE, and 1453 CE eruptions), which happen to be paced in a manner that projects onto an apparent multidecadal (60-70 year period) “oscillation”. Past studies have indeed noted the coincident multidecadal pacing of explosive volcanic activity in past centuries (i.e. Ammann and Naveau (2003)).
A spectral analysis of a simple “energy balance” climate model driven with volcanic-only, solar-only, and volcanic+solar forcing (see article) shows that there is indeed a multidecadal spectral peak in the response of surface temperatures to natural radiative forcing and that peak arises from the volcanic forcing alone. We conclude that the apparent AMO-like signal during the last millennium is a consequence of the coincidental multidecadal pacing by episodes of explosive volcanic forcing.
The available evidence both from observations and current-generation climate models, in summary, does not provide any support for an internal AMO-like oscillation in the climate system.
That doesn’t mean that there aren’t interesting questions left to address here. Our planned future work will examine the next generation (CMIP6) coupled models to see if improved representations of ocean and atmospheric dynamics might somehow lead to modes of internal decadal/multidecadal variability that are not evident in the CMIP5 models. And it will be instructive to analyze the considerably more extensive networks of paleoclimate proxy data that have become available since our 1995 analysis. Of particular interest is whether the multidecadal oscillations in the actual paleoclimate proxy data show the same relationship with volcanic forcing demonstrated in the last millennium simulations.
Concluding Thoughts
There are several lessons in this tale. One is that scientists must always be open to revising past thinking. That is part of the critical scientific process—what the great Carl Sagan referred to as the “self-correcting machinery” of science. Two decades ago there seemed to be both observational evidence and modeling evidence (if rather limited) for the existence of a multidecadal AMO in the climate system. My own work supported that interpretation, and indeed it was I who gave this beast a name. The scientific community ran with the concept, and numerous scientists—even some at our leading research laboratories like the aforementioned GFDL—continued to misapply it in a way that downplays some critical climate change impacts like the warming of the North Atlantic and the increase in Atlantic hurricane activity associated with it.
Now we have come full circle. My collaborators and I, over the past decade, have continued to investigate the origins of the putative AMO signal and have been led inescapably to the conclusion that the AMO (unlike, say, R.O.U.S.) doesn’t actually exist. It’s an artifact, during the historical era, of competing anthropogenic (greenhouse warming and sulphate aerosol cooling) drivers and, during the earlier period, an artifact of the fact that volcanic forcing happens to have displayed a roughly multidecadal pacing in past centuries.
A scientist has to admit when they are wrong. Unfortunately for all of us, my colleagues and I weren’t wrong about the unprecedented warming revealed by the now iconic “Hockey Stick” curve, despite the unrelenting attacks on it by climate change deniers over the past two decades.
But I was wrong about the existence an internal AMO oscillation when I coined the term twenty years ago.
Nonetheless, some very good science has been done by a number of researchers and groups around the world in pursuing this matter. And we have learned quite a bit, for example, about the true origins of multidecadal climate variability, and prospects for long-term climate prediction.
That, in fact, is science (and Science) working the way it’s supposed to.
References
- M.E. Mann, J. Park, and R.S. Bradley, "Global interdecadal and century-scale climate oscillations during the past five centuries", Nature, vol. 378, pp. 266-270, 1995. http://dx.doi.org/10.1038/378266a0
- T.L. Delworth, and M.E. Mann, "Observed and simulated multidecadal variability in the Northern Hemisphere", Climate Dynamics, vol. 16, pp. 661-676, 2000. http://dx.doi.org/10.1007/s003820000075
- J.R. Knight, R.J. Allan, C.K. Folland, M. Vellinga, and M.E. Mann, "A signature of persistent natural thermohaline circulation cycles in observed climate", Geophysical Research Letters, vol. 32, 2005. http://dx.doi.org/10.1029/2005GL024233
- G. Müller-Plath, "Internal Multidecadal and Interdecadal Climate Oscillations: Absence of Evidence Is No Evidence of Absence", Frontiers in Earth Science, vol. 8, 2020. http://dx.doi.org/10.3389/feart.2020.559337
- D.T. Shindell, G.A. Schmidt, M.E. Mann, and G. Faluvegi, "Dynamic winter climate response to large tropical volcanic eruptions since 1600", Journal of Geophysical Research: Atmospheres, vol. 109, 2004. http://dx.doi.org/10.1029/2003JD004151
- C.M. Ammann, and P. Naveau, "Statistical analysis of tropical explosive volcanism occurrences over the last 6 centuries", Geophysical Research Letters, vol. 30, 2003. http://dx.doi.org/10.1029/2002GL016388
First, it wasn’t YOU that was wrong — it was a thesis. Second, that thesis was correct twenty years ago. That is, it represented a logical conclusion based on all the available evidence. Third, that thesis has now been shown to be false. The delightful writer (and rather cranky) Stephen J. Gould wrote a number of essays about past scientists who are now ridiculed for their incorrect beliefs, but whose conclusions were justifiable given the state of knowledge at their time. Charles Babbage invented the computer in 1840. It was a mechanical monstrosity requiring thousands of precisely cut gears, and was never built. It would have been a waste of time and money to build it back then, because people weren’t sharing kitten photos and playing games over a gear-driven Internet. An idea can be wrong at one time and right at another. It all depends upon the context.
Thank you for always be open to revising past thinking and being willing to challenge your own, earlier ideas. It’s a model for us all, not just climate scientists.
“Thank you for always be open to revising past thinking and being willing to challenge your own, earlier ideas. It’s a model for us all, not just climate scientists.”
Indeed it is, but Mike undermines the effect of :
“scientists must always be open to revising past thinking. That is part of the critical scientific process…’
by invoking the wrong exemplar.
A lot of good people , from his Cornell mentors Harold Urey and Phil Morrison, to Johnny Carson , Ted Koppel , and most of all Steve Schneider, tried to get ” The great Carl Sagan” to apply the “self-correcting machinery” of science. ” to his own ” nuclear winrter ” campaign, but he would not listen and refused debate.
Having written, in Foreign Affairs in 1983 that :
“Apocalyptic predictions require, to be taken seriously, higher standards of evidence than do assertions on other matters where the stakes are not as great.”
Carl ignored the erosion of his predictions by generations of better climate models, and went on stonewalling until the the end of his days. It is good to see that Mike has learned from that excellent astronomer’s worst mistake.
You can read a summary of this scientific meltdown in Nature :
https://www.nature.com/articles/475037b
I’m dumbfounded. The AMO index accounts for a few percent of temperature anomalies for the past 170 years, and does so at a high level of significance. What was I analyzing?
Russell, thank you for that utterly irrelevant tale of a great scientist being wrong in the past. However, I think that the lesson to be drawn here is more one of the hazards of drawing conclusions based on limited data–particularly when those conclusions bear on the presence or not of a “cycle” in that data. This is because in any system where there is an equilibrium, excursions away from said equilibrium will likely be followed by a return toward–and possibly an overshoot–of the equilibrium. This will be an oscillation or a quasi-oscillation in only a small proportion of systems. And then there is the fact that humans love–just LOVE–oscillations. They give us predictability without our having to do anything to the system.
Russell, here’s a news flash. Carl Sagan is still dead. He is a stiff, bereft of life and so on. His legacy for good or ill is a fait acompli–and it was overwhelmingly mostly a legacy for good. The Nuclear Winter debate is also dead, although I do think that there is consensus that mass detonation of nuclear warheads would not be a good thing. Maybe it’s time to feel your pain and let it go.
One of the points we lukewarmers have been trying to get across for most of the last decade is that many of the points, findings and extrapolations found in the climate conversation should have been written in pencil rather than pens using indelible ink. Thank you for highlighting another example.
This is going to be a very, very big deal on the Gulf coast. Since the 1990’s we’ve been told that we were going to go through a tough 30 year period and sure enough it came true. And we’ve been told to just hold on, that slower tropical cyclone seasons were just around the corner. That the AMO has been responsible for the extreme damage and hardship of hurricanes since 2005 has been a given. We hear it from TV meteorologists and in weather blogs constantly. Google Houston-AMO-Hurricanes to see just how often local media has linked the recent devastating storm seasons to the AMO.
And what about the model projections that AGW induced atmospheric changes will increase wind shear and depress the number of tropical cyclones? Will tropical cyclones continue to increase in both strength and number?
We’ve been told to go ahead and take on that new 30 year mortgage, re-nourish that beach, rebuild the beachside highways (most of which has been federally funded); it’s all going to get better soon. That last 20 years have been tough on the Gulf coast. If folks knew there was no relief in sight I think many would be making different choices. People don’t like it when promises are broken and many will see this as just that.
Be prepared for a rash of interview requests from the Houston area media.
Here is an example of what we can expect when this story is more well-known.
Note they cite NOAA’s web story that blames the AMO on the 2000-2020 hurricane increase.
https://www.wsgw.com/humans-not-nature-may-be-changing-atlantic-hurricane-cycles/
When the facts change, I change my mind. What do you do?
— John Maynard Keynes
Dear Russell,
You are wrong about nuclear winter, and Carl Sagan was right. Please see our latest work on it with modern climate models, at http://climate.envsci.rutgers.edu/nuclear/#Publications. In particular, paper 29 shows results from the NASA GISS model in 2007, and paper 9, from 2019, shows that simulations with WACCM agree almost perfectly. And you can see a recent 2020 article in Nature about our work at https://www.nature.com/articles/d41586-020-00794-y, not the assertions in your 10-year old letter.
Thanks for the great explanation. And it’s especially valuable that the originator of this, um, meme? should be the one to take it down.
Another lesson, which is especially important in the context of climate, is that sometimes when press accounts present something as consensus, when you ask the scientists themselves you’ll find them arguing about it. So no, the scientific community wasn’t “wrong”, it was in its usual state of still thinking about things. You note that some people doubted already some years back that AMO was self-generated rather than driven by volcanoes or whatever, even if they didn’t have the computers to prove it. Just for the record I’d like to add two more references: B. Booth, et al. (2012), “Aerosol Haze Implicated as a Prime Driver of Twentieth Century North Atlantic Climate Variability.” Nature 484 228-32 [doi.org/10.1038/nature10946]; A. Clement et al. (2015), “The Atlantic Multidecadal Oscillation without a Role for Ocean Circulation.” Science 350 320-24 [doi:10.1126/science.aab3980].
@4 (Barton Paul Levenson):
Could it be a simple overfitting explanation?
I have noted similarities of this with medical analyses of pandemics and debugging intermittent problems with computers.
For the latter, my first computer was an IBM 7074 in the Penn State Computer Center, 1967.
It suffered quasi-periodic crashes, for no obvious reason. Many technical explanations were suggested.
It turned out that when it was cold, one operator (who worked a particular shift) wore a fur coat they through over the CPU cabinet and static electricity caused trouble, sometimes.
Ray & Alan
Numbers talk
As the Naure letter notes, perseverence in denial cannot overcome the two order of magnitude disparity betweem Crutzen’s “Twilight At Noon ” and the Biblical biblical forty days and forty nights of Apocalyptic darkness. Carl conjectured, and hired a PR firm to propagandize. before the fact of peer review.
Science is what it is, not what Planetary Society fans want it to be,. and the blatantly political P-R campaign Sagan’s sponsors funded remains , as Mike’s co-author. Kerry Emanuel said , and Nature’s lawyers have confirmed.
“Notorious for its lack of scientific integrity”
Scheider and I wrote our 1980’s policy journal TTAP critiques because we agreed that Carl’s florid megahype could ,and would, erode the credibility of climate modeling on the eve of the global warming controversy .
So drop the hagiography, and face the facts: you guys are not helping to overcome the climate policy consequences of Carl’s caampign by denying them, or by recycling and reiterating forty year old radiative forcing parameters as though atmosperic science remains stuck deep as TTAPS in the big chill of the cold war.
Many thanks to Alan for reminding us of the perils of self-citation by linking
http://climate.envsci.rutgers.edu/nuclear/#Publications
All 31 of that that authoratative document’s citations include Alan and the TTAPS authors !
Chris McGrath (2) “Thank you for always be open to revising past thinking and being willing to challenge your own, earlier ideas. It’s a model for us all, not just climate scientists.
Particularly that it can and will be used against him by the deniers (“he admitted being wrong in AMO, then he is wrong in everything else he did, or will, claim”). Don’t let anything good to go unpunished … ;-)
Tom Fuller:
Tom, just how are you a “lukewarmer”? A lukewarmer* is somebody who accepts that the globe is warming and it’s our fault, but doesn’t think it will be a problem for him, so doesn’t support collective action to decarbonize the US and global economies. A lukewarmer will bravely go out on a logical limb to defend his freedom to socialize his private marginal climate-change costs, while steadfastly denying the tragedy of those who’ve already paid with their homes, livelihoods and lives. IOW, lukewarmism is a craven refusal to accept responsibility. You, OTOH, are known to support a carbon fee and dividend, which would require you to internalize some fraction of your marginal climate-change costs. AFAICT, that is, you’re not a lukewarmer. Why boast of such a pejorative label when you don’t deserve it?
* I’m aware of Mosher’s and your claim to own the word. The definition I’m using is the widely accepted one. Deal.
@4 “The AMO index accounts for a few percent of temperature anomalies for the past 170 years, and does so at a high level of significance. What was I analyzing?”
The correlation between said index and the remaining variance left after partialing out the main linear trend for the past 170 years?
Of course the REAL task is to show that said index is _actually_ an AMO index measuring an AMO with specific properties as opposed to a measure which only seems to establish an AMO. That is the subject of the article at hand.
This reminds me of the statistical errors made by so many deniers and even some scientists over “the Pause”. There WAS a lack of correlation, it just didn’t necessarily mean there was an actual pause in global warming occurring in the sense deniers were trying to imply. I see far less nefariousness here, but some of the same sorts of thinking. An “index” may _suggest_ something is a “thing” but in no way does an index proves said thing’s existence.
In the statistics of scale development nothing is more common than finding an index which is reliable in that it shows consistent correlations yet entirely invalid as an indicator of the property of actual interest. Look no farther than “intelligence” tests which are in fact quite reliable, yet of quite questionable validity in the general sense desired by many.
An apple falls towards the ground because it is attracted to the inner core of the Earth.
(It’s also possible that Newton’s first prediction was wrong)
Chris Crawford nailed it when he spoke of “truth” or “correctness” being a function of ‘the time’, when forming a thesis based on best available science. Any student of “history & Philosophy of Science” will be well aware of the manner in which scientific knowledge advances. Person X Develops a theory of understanding the current observed facts & puts it out there, for review, debate & testing. Person Y, Z etc do their damnedest, repeat & when finding supporting evidence, agree, tweak or upended the theory when new evidence emerges that contradicts the theory. As Mann recognises, it is the way science works… and moreover, why it is the best method we have to begin to understand the world around us.
As an initial reaction to this news of the demise of the poor old AMO, having read a fair amount on the AMO and its 60 year periodicity, my memory is that in the past I did seem to be finding a lot of literature reporting signs of AMO, a 60-year wobble in regional climate proxy data [?from the likes of S America & Africa?] While this seemed to be more like a shifting-rain-belt type thing rather than wobbling global temperature, and while it could also be also an artifact of ‘volcanic coincidence’, my memory [which isn’t entirely trustworthy] was of these phenomenon being found running back a fair few centuries making such a ‘volcanic coincidence’ less understandable at face value.
In other words, there is quite a lot of work built on the presence of an AMO that will need revisiting give this news of the demise of the poor old AMO.
RS 3: A lot of good people , from his Cornell mentors Harold Urey and Phil Morrison, to Johnny Carson , Ted Koppel , and most of all Steve Schneider, tried to get ” The great Carl Sagan” to apply the “self-correcting machinery” of science. ” to his own ” nuclear winrter ” campaign, but he would not listen and refused debate.
BPL: And all these years later, 25 years after Sagan’s death, Seitz is STILL obsessing about this. Time to move on, Russell!
AR 10,
Thanks for coming in here! I’ve tried to keep up the good fight–my involvement with the whole debate was quite peripheral–but while I might have affected the folks at RealClimate, Russell is still convinced that Sagan was an evil hippie peacenik pushing junk science. BTW, I have enjoyed your papers. Can you give me any details on the plume height algorithm you use? It seems to me that a crucial difference between “nuclear winter” and “nuclear autumn” papers is the conclusion about how high the aerosols get lofted; i.e., do they reach the stratosphere or not.
MalAdapted, I do not wish to divert this thread. I will just note that you are (as usual, I think) spectacularly incorrect in your definition of ‘lukewarmer,’ my self-placement within that group, the etymology of the term and the policy implications of ‘lukewarmism.’ So you’re 0 for the comment.
1. A ‘lukewarmer’ (according to the original definition–lots of people have put the label on their shirt in the past decade, many without understanding what it means) is someone who accepts the physics of climate change but is willing to bet on sensitivity being at the low end of the 1.5C-4.5C range posited by the IPCC, among others. Specifically we think it is somewhere under 3C.
2. I have in the past published a long list of policy actions I advocate. They do include a carbon tax, but much more besides.
3. Neither Steve Mosher nor myself have ever claimed to have originated the term ‘lukewarmer.’ At most we were early adopters. I think it might be more accurate to say that Steve put the first stake in the ground regarding its definition as being less than 3C.
There are people who have adopted the term to escape association with climate ‘skeptics.’ There are people who support the idea because they think it describes a ‘middle ground’ regarding climate impacts and the proper policies to address climate change. Some grabbed at the chance to stop being labeled as ‘deniers,’ surely one of the most odious terms in use, although much of the sting was removed from the term when Barack Obama and James Hansen were labeled ‘deniers’ by climate activists.
However, speech and labels have proven to be not useful in advancing sound climate and environmental policy. I think this comment is largely a waste of space on this thread.
There are no policy requirements for being a lukewarmer. Although my policy preferences are more aggressive than those of some lukewarmers, some have similar lists of what we should do. The term describes people who have opinions about models, not politics.
Has anyone from the NOAA weighed in on this with their thoughts? The NOAA has (still) an AMO Index page on their site.
https://psl.noaa.gov/data/timeseries/AMO/
RE: 24 Thomas Fuller says “There are no policy requirements for being a lukewarmer.”
No. Perhaps there are more like me who both understand the science and believe much (most) of it but have a hard time believing any government (democratic/totalitarian) can control the weather. I get it. Weather isn’t climate. Which means one has to believe that successive governments (democratic/totalitarian) can control the weather for 30+ years consistently to make any difference. And to make any difference globally would require consistent government control globally.
And it’s that bit about global government control that bothers me. Well that and who decides what’s the best climate globally (of course) to aim for and how much colder and longer do Canadian (among others) winters have to get before it’s considered a win?
Regarding the lukewarmers. I tend to normally agree with Mal Adapted, but I struggle with his definition of lukewarmer. I always understood lukewarmer to mean someone who accepts the climate is changing, but that it wont change much so wont have serious consequences for humanity, or that even substantial change wont be serious. This follows fairly naturally from the word. It seems I’m not alone:
https://en.wiktionary.org/wiki/lukewarmer
Such people generally oppose mitigation (maybe with some exceptions), which follows fairly naturally from being a lukewarmer. They appear to especially oppose government getting involved when I read their stuff. Of course this might be driving their lukewarmer leanings.
Thomas Fuller:
Oh, come on, that’s hardly distinct from the mainstream, science-respecting position. The excellent David Roberts, writing in Vox in 2017, applies the ‘lukewarmer’ label to the likes of Rex Tillerson, who was briefly Trump’s Secretary of State:
You, OTOH, appear to acknowledge the cost in money and tragedy implied by an ECS “somewhere under 3C”; and you have supported ‘serious’ policy, on RC and elsewhere. You’re therefore not a lukewarmer by definition. Hey, argue with David Roberts, not with me 8^D!
Look, I recognize the early history of the word among Curry’s old claque. I get that you’d like to reclaim it for whatever you think distinguishes you from a run-of-the-mill ‘climate realist’. But ‘lukewarmer’ is now firmly attached to the species of denier Roberts describes. Isn’t there some other pithy label you can wear on your shirt?
RE. Thomas Fuller @24
I would assume this bit of hyperbole is based on Naomi Oreskes’ opinion piece on a new kind of denialism—the belief in a need for nuclear power in decarbonization. This hardly represents a *label* being foisted on Obama and Hansen by climate activists. But, whatever.
Mal Adapted, the existence or lack thereof of an AMO is surely more important than a precise labeling of who is or is not a member of a minor fraction of those following the climate conversation.
I am a lukewarmer by every definition of the term that I am aware of. And I know that I advocate many policies that others do not, including some who also call themselves lukewarmers.
David Roberts is a long-time climate activist who occasionally writes brilliant pieces. It does not surprise me that he searches for a term to characterize Tillerson, former CEO of Exxon, who Roberts must perceive as a bitter political foe. Why he landed on the term lukewarmer is anyone’s guess. Five years previously Roberts would have used the term ‘denier.’ But I think the term he was searching for is ‘Republican.’
I have long held that those who are overly interested in labeling tend to be more interested in excommunication than communication. But I don’t find this conversation to be nearly as interesting as the AMO.
Thomas Fuller:
Heh. You’re the one who gratuitously labeled himself a ‘lukewarmer’. How did you think we’d respond 8^)?
barn E rubble (26) “ I understand the science ”
That’s … debatable given what you write next:
bEr(26) “and believe much (most) of it but have a hard time believing any government (democratic/totalitarian) can control the weather. I get it. ”
No, you don’t:
bEr(26) “Weather isn’t climate. Which means one has to believe that successive governments (democratic/totalitarian) can control the weather for 30+ years consistently to make any difference”
No, it does not mean that. It means that slowing/reversing the changes to the climate caused by humans, DOES NOT require the ability of the governments to CONTROL … weather every day for the next “30+ years”. It requires though reducing the human GHGs global FORCING that causes the climate changes in the first place.
The same way like loosing weight does not require predicting and CONTROLING instantaneous changes in metabolic activity in every cell in your body for many months ahead (since the sum of these would affect whether you gain or lose weight) – I’d suggest first try to eat less and to move more.
bEr(26) who decides what’s the best climate globally (of course) to aim for and how much colder and longer do Canadian (among others) winters have to get before it’s considered a win?
Nobody decides _that – given the high mixing rate – the reductions in emissions of CO2 have global, not regional, targets. As for “what is considered a win” – I’d say a win is to slow the warming and then stabilize the climate as close as possible to what we USED TO HAVE before we started changing it (the precautionary principle). The further above that point we are – the bigger the damage to the ecosystems that evolved in colder climates and the higher the risk of instability, positive feedbacks, and runaway climate change, which, by lowering our crops, may end us as a civilization.
Compared to that – keeping the Earth warmer than it used to be just so Canadian winters are more comfortable – seem rather self-centered and short-sighted. Not very Canadian, eh?
The Economist notes that the Pacific oscillation still has the power to move markets :
https://www.economist.com/finance-and-economics/2021/01/12/commodity-prices-are-surging?utm_campaign=the-economist-today&utm_medium=newsletter&utm_source=salesforce-marketing-cloud
nigelj:
Huh. You’re under no obligation to agree with me, of course, but AFAICT you, me, Wiktionary and David Roberts all agree closely on the definition of ‘lukewarmer’. OTOH, again AFAICT, Tom’s definition matches that of Tamsin Edwards in 2015:
The problem is that by 2015, anthropogenic climate change was already taking a toll in money and tragedy, that has mounted rapidly since then. For the victims, one presumes the current warming is plenty ‘large’ enough. Even under modal ECS estimates, in the absence of “strong”, i.e. effective, mitigation efforts there’s ‘substantial’ risk future warming could be even larger, causing orders of magnitude greater costs. The self-described lukewarmers’ refusal to acknowledge that uncertainty is not their friend, and their breezy exclusion of the upper half of the consensus ECS range, makes them climate-science denialists. Their willingness to deprecate or dismiss the tragedy of AGW’s victims to date in arguing against ‘strong’ mitigation measures (i.e. any that take the profit out of fossil fuel production), makes them despicable. IMHO, of course.
That really isn’t you, is it, Tom?
#32, piotr–
Not to mention the fact that on current climate trends, the noble tradition of outdoor hockey is at risk:
https://nhl.nbcsports.com/2021/01/08/outdoor-hockey-traditions-under-shadow-of-climate-change/
“Lin et al. (2019) argues for two different sources for AMO variability, identifying 50–80 year and 10–30 year AMOs that are associated with different underlying dynamics.”
There’s a clear correlation with the proposed 10-30 year variability and the Earth’s core, rotation rate cycle and earthquake/volcanic activity:
….
Specifically, the team noted that around every 25-30 years Earth’s rotation began to slow down and that slowdown happened just before the uptick in earthquakes. The slowing rotation historically has lasted for 5 years, with the last year triggering an increase in earthquakes.
….
https://www.forbes.com/sites/trevornace/2017/11/20/earths-rotation-is-mysteriously-slowing-down-experts-predict-uptick-in-2018-earthquakes/?sh=bc379706f243
..
I’ve emailed the correspondence author of the Lin et al. (2019) paper, hopefully bringing the correlation to their attention.
Physics Question For Any Experts,
I haven’t paid much attention to the AMO over the years, and one reason I haven’t is that I have never seen a physical narrative to explain it as an internal phenomenon… like with ENSO, where the wind piles up the water yadda yadda, it sinks yadda yadda, and so on.
Is there perhaps a paper that offers such a description of an internal physical process that might produce variations over the multi-decadal periods? Even if we now have concluded that such speculation was wrong, I am curious to see what people were thinking.
[Response: Actually, there are some models that do produce an intrinsic multidecadal oscillation whose period is set by gyre-scale and overturning-scale circulations that have decadal-to-multidecadal adjustment timescales. See the Delworth & Mann and Knight et al articles referenced in the piece. The point, however, is that these very much now appear to be the exception rather than the rule, and the mechanisms are not consistent from one model to the next. – mike]
Personally Russell, if I where the PDO I would be worried.
MWP – Gone
AMO – Gone
PDO – ???
Any other TLA should be concerned
“..like with ENSO, where the wind piles up the water yadda yadda,..” – zebra
There’s no direct evidence of easterlies being strong enough to cause deep ocean upwellings. The literature cites equatorial winds as being constantly light. Ocean bottom tidal forcing due to new gravitational theory is a better explanation imo. It can similarly account for the AMO & PDO.
@38s/where/were/
sorry
Munk & Wunsch claimed that it was either the wind variation or tidal forces — but what causes the wind to change on other than an annual cycle? The farther it veers from the annual cycle, the more tenuous the connection to an external forcing. The answer likely lies in the synchronization of tidal cycles with the annual cycle, which can create all the plausible physically aliased periods necessary to create the interannual variation observed. This will generate the 3.8 and 3.9 year cycles corresponding to the primary Mf and Mm long-period tidal factors and over 100 years for the crazy 9-day Mt tide, of which there are nearly exactly 40 periods per year. So when this synchronizes against a strong annual impulse it will slowly build up over the course of decades, only to reverse as it destructively interferes with the annual cycle.
The geophysics connection to this mechanism is the Earth’s length-of-day variations, which happen to follow the tidal factors at the non-aliased Mf, Mm, Mt scales rather precisely but also indications that it follows the potentially aliased long-term variations. As S.Marcus formerly of NASA JPL wrote, the LOD variations follow the same variation as the 40-60 year period of AMO:
“Does an Intrinsic Source Generate a Shared Low-Frequency Signature in Earth’s Climate and Rotation Rate?”
https://journals.ametsoc.org/view/journals/eint/20/4/ei-d-15-0014.1.xml
And that’s where the attribution arguments start to set in. Will the angular momentum variation kick in tectonic motions that may set off volcanic activity?
And consider that the ocean does not respond as a solid body would to angular momentum variations, which is where the solution to Laplace’s Tidal Equations kicks in, and only certain scientists know how to solve this ;)
#38, KW–
Nah, too easy.
Andrew: Since the 1990’s we’ve been told that we were going to go
AB: No. You were told in no uncertain terms that if you voted GOPper your state WILL cease to exist. That you pretend that ONLY GOPpish “tolds” count is just more evidence that those who vote GOPper are dumb as dirt. Do you disagree?
Paul Pukite: I’m predicting that when the Earth’s rotation rate can soon be measured with high accuracy in near real-time, it will be seen to speed up during a solar eclipse. (See Allais Effect & Phobos eclipse causing Marsquakes)
Newton/Einstein gravity theory is not sacred nor separate from climate science.
Climate science is after all, a theory of everything.
No 43. You got that right if we are speaking of Florida for instance it won’t take all that much sea level rise before it becomes a few marshy islands. Though I do think the developer just outside Little Rock was “probably” stretching things some years ago with the sign advertising future ocean front property! That was about 20 years ago if I remember right.
Alan Lowey(38): “There’s no direct evidence of easterlies being strong enough to cause deep ocean upwellings. Ocean bottom tidal is a better explanation imo.”
And they are strong enough to drive the surface currents several km above them?
And how being tidal, do they reverse every few years to shut down the upwelling and reverse the surface currents and winds during El Nino?
That’s the 14.765 day Msf tidal factor, which is a multiplicative combination of the 13.66 day Mf lunar tidal factor with the annual Sa solar tidal factor. This rotation rate variation is already observed in the Earth’s length-of-day (LOD) measurements maintained by https://hpiers.obspm.fr/eop-pc/index.php
NASA JPL is all over this one, or they were at one time, until it slipped through the cracks. From a proposal by Perigaud et al
There is also a very strong annual impulse that you can see from the SST data along the equator — critical data that is filtered out by agencies such as NOAA. See the contents of this directory called “ensostuff” https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/detrend.nino34.ascii.txt
Beware throwing away the baby with the bathwater with respect to overzealous filtering of data. All this info can go into trying to solve ENSO and AMO simultaneously via Laplace’s Tidal Equations, assuming the only difference is the unique standing wave modes of the two ocean basins.
https://geoenergymath.com/2020/12/22/overfittingcross-validation-enso%e2%86%92amo/
RE. ‘lukewarmer’ @24
This is a very bad bet on multiple levels.
Pure physics tells us that the climate sensitivity to CO2 and the water vapor feedback is at least 2.0C. Anything less than that would require the net sum of all the other feedbacks to be negative, a possibility that is so improbable as to be next to impossible. The only reason the IPCC’s low end was set at 1.5C in the last assessment was due to studies utilizing the instrumental record giving lower sensitivities which more recently have been shown to have been inadequate for various reasons. None of the other methods used, model ensembles, constrained models, and the paleo record result in a possible bottom end of the range at less than 2.0C. Which is to be expected based on the physics.
The next IPCC assessment report is expected to raise that bottom end back to 2.0C. And nevertheless, the most likely sensitivity remained at about 3.0C with the most current science based on the paleo record saying that the odds are in favor of the net long term feedbacks beyond water vapor being greater than 1.0C. Thus there is a greater likelihood of the sensitivity being greater than 3.0C rather than less. Let me repeat that, the odds are greater that the sensitivity is greater than 3.0, not less. That’s the science so being willing to bet that the sensitivity is lower than 3.0C when the evidence shows otherwise is a form of science denial.
Anyway, If the climate sensitivity were on the low side of the probable range why would that change anything?
It certainly would not “buy us time” because we’ve already run out of time.
Consider that it has been shown that the last time CO2 levels were at 400 ppm sea levels were somewhere around 65 feet higher than today. This brings to mind that the consequences to increases in CO2 levels are not instantaneous, it takes time for the climate and the planet to reach a new equilibrium. We’ve already created a new state with significant future consequences yet to be realized.
Of course the slowest response to warming is the melting of ice. Take a chunk of ice out of a freezer and leave it on the counter and with that almost instantaneous change in temperature of approximately 40C (70F) it still takes a significant amount of time for that ice to melt. Likewise for the glaciers of the earth. There is already enough CO2 to melt a lot of ice and to significantly raise sea levels (65 feet give or take which is really really going to be bad for mankind) and the only way to reverse sea level rise is to not only just stop emissions, but to return the atmospheric levels back to preindustrial. That’s hard to do.
Every single molecule of CO2 emitted into the atmosphere by mankind matters. Every single bit. We are facing a climate emergency and the sooner people understand that and the sooner significant action is taken the better. Believing that climate sensitivities are on the lower end of the probable range does nothing to moderate what our appropriate responses should be because either way we are not doing anywhere close to enough. The only question now with what that exact sensitivity is: what future generation gets totally screwed first?
Claiming to be a *lukewarmer* does nothing to help the situation, it is just a distraction.
Humans have been collecting large quantities of accurate and global climate data for less than 100 years, probably for only 70 years. Before that data collection was not widespread over the surface of the earth, and the measurements were suspect due to instrument quality and siting errors.
Perhaps in another 100 years we’ll have enough data to make high probability assertions about what the climate is doing, but not yet.
Mike: why is the correlation of the AMO with the Pacific MJO not discussed?
….
So, unlike ENSO, which is stationary, the MJO is an eastward moving disturbance of clouds, rainfall, winds, and pressure that traverses the planet in the tropics and returns to its initial starting point in 30 to 60 days, on average.
https://www.climate.gov/news-features/blogs/enso/what-mjo-and-why-do-we-care