A guest commentary by Kyle Swanson – University of Wisconsin-Milwaukee
I am quite humbled by the interest that has been generated by our paper “Has the climate recently shifted?” (Swanson and Tsonis, 2009), and would like the thank the RealClimate editors for the opportunity to give my perspective on this piece.
Before delving into the paper itself, a few words about the place of our work in the global warming “debate” are in order. A quote from the early 20th century Viennese polymath Egon Friedell (which I ran across in the wonderful book Cultural Amnesia by Clive James) captures the situation better than any words I could ever weave;
Electricity and magnetism are those forces of nature by which people who know nothing about electricity and magnetism can explain everything.
Substitute the words “modes of natural climate variability” for “electricity and magnetism,” and well…, hopefully the point is made.
It first needs to be emphasized that natural variability and radiatively forced warming are not competing in some no-holds barred scientific smack down as explanations for the behavior of the global mean temperature over the past century. Both certainly played a role in the evolution of the temperature trajectory over the 20th century, and significant issues remain to be resolved about their relative importance. However, the salient point, one that is oftentimes not clear in arguments about variability in the climate system, is that all else being equal, climate variability and climate sensitivity are flip sides of the same coin. (see also the post Natural Variability and Climate Sensitivity)
A climate that is highly sensitive to radiative forcing (i.e., responds very strongly to increasing greenhouse gas forcing) by definition will be unable to quickly dissipate global mean temperature anomalies arising from either purely natural dynamical processes or stochastic radiative forcing, and hence will have significant internal variability. The opposite also holds. It’s painfully easy to paint oneself logically into a corner by arguing that either (i) vigorous natural variability caused 20th century climate change, but the climate is insensitive to radiative forcing by greenhouse gases; or (ii) the climate is very sensitive to greenhouse gases, but we still are able to attribute details of inter-decadal wiggles in the global mean temperature to a specific forcing cause. Of course, both could be wrong if the climate is not behaving as a linear forced (stochastic + GHG) system.
With that in mind, our paper is fundamentally about inter-decadal variability in the climate system and its role in the evolution of the 20th century climate trajectory, as well as in near-future climate change. The climate system has well known modes of variability, such as the El Niño/Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO), that are active on inter-annual time scales. We are interested in how this short time-scale (from the climate perspective!) variability impacts climate anomalies over multi-decadal time periods.
What we find is that when interannual modes of variability in the climate system have what I’ll refer to as an “episode,” shifts in the multi-decadal global mean temperature trend appear to occur. I’ll leave the details of these episodes to interested readers (here and here), as things get pretty technical. It’s sufficient to note that we have an objective criteria for what defines an episode; we aren’t just eyeballing curves. The climate system appears to have had three distinct “episodes” during the 20th century (during the 1910’s, 1940’s, and 1970’s), and all three marked shifts in the trend of the global mean temperature, along with changes in the qualitative character of ENSO variability. We have also found similar types of shifts in a number of model simulations (both forced and unforced) that were run in support of the IPCC AR4 report.
The contentious part of our paper is that the climate system appears to have had another “episode” around the turn of the 21st century, coinciding with the much discussed “halt” in global warming. Whether or not such a halt has really occurred is of course controversial (it appears quite marked in the HadCRUT3 data, less so in GISTEMP); only time will tell if it’s real. Regardless, it’s important to note that we are not talking about global cooling, just a pause in warming.
What’s our perspective on how the climate will behave in the near future? The HadCRUT3 global mean temperature to the right shows the post-1980 warming, along with the “plateau” in global mean temperature post-1998. Also shown is a linear trend using temperatures over the period 1979-1997 (no cherry picking here; pick any trend that doesn’t include the period 1998-2008). We hypothesize that the established pre-1998 trend is the true forced warming signal, and that the climate system effectively overshot this signal in response to the 1997/98 El Niño. This overshoot is in the process of radiatively dissipating, and the climate will return to its earlier defined, greenhouse gas-forced warming signal. If this hypothesis is correct, the era of consistent record-breaking global mean temperatures will not resume until roughly 2020. Of course, this contrasts sharply with other forecasts of the climate system; the purple line roughly indicates the model-based forecast of Smith et al. (2007) , suggesting with a warming of roughly 0.3 deg C over the 2005-2015 period.
Why would anyone in their right mind believe what I’ve just outlined? Everything hinges on the idea that something extraordinary happened to the climate system in response to the 1997/98 super-El Niño event (an idea that has its roots in the wavelet analysis by Park and Mann (2000)). The figure to the left shows the spatial mean temperature over all grid boxes in the HadCRUT3 data set that have continuous monthly coverage over the 1901-2008 period. While this provides a skewed view of the global mean, as it is heavily weighted toward North America, Europe and coastal areas, unlike the global mean temperature it has the cardinal virtue of being a consistent record with respect to time. The sole exclusion in the figure is the line connecting the 1997 and 1998 temperatures.
Now, anomalous behavior is always in the eye of the beholder. However, the jump in temperature between 1997 and 1998 in this record certainly appears to pass the “smell test” (better than 3 standard deviations of interannual variability) for something out of the ordinary. Nor is this behavior dependent on the underlying time interval chosen, as the same basic picture emerges for any starting time up until the 1980’s, provided you look at locations that have continuous coverage over your interval. Again, as the temperature anomaly associated with this jump dissipates, we hypothesize that the climate system will return to its signal as defined by its pre-1998 behavior in roughly 2020 and resume warming.
What do our results have to do with Global Warming, i.e., the century-scale response to greenhouse gas emissions? VERY LITTLE, contrary to claims that others have made on our behalf. Nature (with hopefully some constructive input from humans) will decide the global warming question based upon climate sensitivity, net radiative forcing, and oceanic storage of heat, not on the type of multi-decadal time scale variability we are discussing here. However, this apparent impulsive behavior explicitly highlights the fact that humanity is poking a complex, nonlinear system with GHG forcing – and that there are no guarantees to how the climate may respond.
Park, J. and M.E. Mann, 2000: Interannual Temperature Events and Shifts in Global Temperature: A Multiple Wavelet Correlation Approach. Earth Interactions, 4-001, 1-36.
Swanson, K.L. and A.A. Tsonis, 2009: Has the climate recently shifted? Geophysical Research Letters, 36, doi:10.1029/2008GL037022.
388 Responses to "Warming, interrupted: Much ado about natural variability"
Thank you for the guest appearance.
You look at various temperature histories and assert that something has happened, and that thing has some persistence.
While I don’t see much gain in analysing every last wiggle, a claim of a 10-some year excursion from the mean would seem to require some preliminary physical explanation. What is happening? Is there some observable change in ocean or atmospheric circulation, some redistribution of heat, some feedback effect that then changes the radiative balance?
While the 1998 El Nino was certainly strong, I will need more convincing that the aftermath reflects an ‘episode’ that is outside the usual variability.
[Response: On a general note, my thanks to everybody for all their thoughtful comments. Kyle himself is out of town at the moment but we decided it was time to go ahead and post this anyway while the paper was still fairly fresh off the presses. I will do my best to provide some feedback to the comments in Kyle’s absence. (I am pleased to say, by the way, that Kyle was my first grad student at U. of Chicago). As for this comment itself, yes indeed it is hard to do decadal variability with a relatively short record, but given that there is a need to try to sort these things out without waiting until CO2 has already doubled,one must simply do the best one can with the available data and hope the picture becomes clearer as time progresses. –raypierre]
Hank Roberts says
> more convincing
later papers citing the above-cited paper on wavelet analysis:
Jacob Mack says
Thank you Mr. Swanson for that thoughtful and fair–balanced analysis.
save gaia says
Maybe this annomaly you speak of has something todo with the montreal protocol?
wayne davidson says
Raypierre, its completely counter intuitive to suggest that there will be a pause in Global Temperature warming. Unless there is a change in long term weather, world wide, in a sustained fashion, which is possible but a rare event. What I see recently is yearly variations caused by regional weather scenarios. In the case of this summer, to make it familiar, the NE North American Coast and most of Canada is cooler by extensive periods of cloud coverage, cooling caused by this region clashes with the US South extreme heat, given less bouts of clouds up North, the North American warming record would have been amazingly strong, but permanent cloud episodes over one region or another travel, never last forever, as such not causing a permanent shift in the temperature record (unless the clouds cover or not wide swats of the Polar regions). Conversely, one side of the Hemisphere may be cloudy , but the other not so. Despite NAO and El-Nino periods. The over all recent result, the world wide average in temperature, has increased. I would suggest comparing peak to peak average temperature captures during weighted El-Nino events (during the time they occur, if they can be compared equally this would be a telling graph), instead of considering year to year records as a means of reducing ENSO effects on the temperature record, ENSO being largely a heat exchange between air and sea causing great changes in cloud distribution world wide.
Time will show that the proposed pause in temperature increase is a model artifact… I doubt very much in such an occurrence.
[Response: Wayne, please note that this is Kyle’s article not mine, though I did encourage him to write it for us. I think the interesting question raised (though not definitively answered) by this line of work is the extent to which some of the pause in warming mid-century might have been more due to decadal ocean variability rather than aerosols than is commonly thought. If that is the case, then a pause or temporary reduction in warming rate could recur even if aerosols are unchanged. Learning how to detect and interpret such things is important, lest a temporary pause be confused with evidence for low climate sensitivity. –raypierre]
Yvan Dutil says
This observation look very much like the so called “Magic Door¨. This looks like a jump from one state of a cahotic attractor to another.
Patrick 027 says
Is there any connection to the AMO?
Hank Roberts says
Are the episodes thought to be actual changes in the amount of heat being radiated by the planet (because the surface of the ocean gets warmer and cooler, does the actual infrared flux from the top of the atmosphere then change as a result)?
If so do we have any baseline satellite record that can be watched assuming we do get another El Nino this fall and winter?
(And would Triana do anything useful, if put up and operating?)
Or are the episodes thought to be changes in where the heat is being carried in the atmosphere/ocean system,
[Response: In the end, these episodes should be primarily thought of as fluctuations in the atmosphere/ocean heat exchange. Think of what would happen if you could pump cold deep water up to the surface, increasing the air/sea temperature gradient and warming the water; that would give you an anomalously large ocean heat uptake. Some of that would result also in a change in the radiation to space, and in particular a change in the net top of atmosphere radiative imbalance. Cloud feedbacks and water vapor feedbacks would affect the translation into TOA imbalance. In any event, such imbalances are at present exceedingly hard to monitor by satellite. –raypierre]
Note: It’s not Raypierre’s post, it’s by Kyle Swanson of “Swanson & Tsonis, 2009”.
Greg Simpson says
Is a linear trend line justified in the first graph? All the forcings seem to be accelerating.
Jim Thomson says
How do I answer the sceptics/deniers who utilise the cooling since 1998, matched with the trend lines in the IPCC reports that show warming climbing while the reality is cooling or at least flat lining?
(Ergo the IPCC is a crock and therefore every thing relating to AGW is also a crock?)
Here in Australia the deniers loaded this question onto Senator Steve Fielding, fresh back from the USA on a “fact finding mission” to the Heartland Institute, Sen Fielding then used his vote in the Senate to block the ETS bill.
If El Nino is put up as the reason why doesn’t the the forecast’s take that into account and show it???
Joel Shore says
Dr. Swanson: One distinction between your analysis and the more conventional ones is the rate of underlying warming that is occurring due to radiative forcings. I notice that your fit to the temperature data from 1979 to 1997 gives a slope very close to 0.10 C / decade, whereas I believe a fit over a longer period (like 1979 to 2008) would give a slope more like 0.16 C / decade. Do you believe that the 0.10 C / decade value is a better estimate of the current forced response to the net radiative forcings on the climate system?
Pat Cassen says
Is the red line schematic, or is there some objective way in which its level is determined? The time at which there is a ‘return to warming’ is somewhat sensitive to this value, right?
Brian Brademeyer says
>>> slope very close to 0.10 C / decade,
Look at the figure again. Looks to me like linear fit goes from -0.3 to +0.55 degrees in 50 years, or 0.17 degrees per decade.
Chris Colose says
Another important paper of recent is by Easterling and Wehner that demonstrates that cooling on timescales of years to a decade or two are not that unusual even when the system is undergoing a long-term warming trend induced by radiative forcing.
I’d also like to extend thanks to Dr. Swanson for discussing his paper, which I believe certainly contains some “different” perspectives, and has also been cited inappropriately on the internets. Unfortunately it isn’t a perspective I would give a lot of predictive power to (and is somewhat too reliant on a particular dataset) but as noted in the post, only time will tell.
Re Jim 11: I don’t think there has been any cooling, nor any “flat-lining” on time scales relevant to present climate change. See https://www.realclimate.org/index.php/archives/2008/01/uncertainty-noise-and-the-art-of-model-data-comparison/, among others here.
The trajectory of the forced climate change is a subtle one; fluctuations due to El Nino and other oscillations (“weather”) have a high amplitude and will obscure the long-term trend if you look at short time scales. And yes, short can be 10 years. 1998 was a outlier warm year due to El Nino. Last year featured a La Nina. Cherry-picking 1998 as a starting point and forcing a linear fit through the noisy data of 10 years since then has little meaning.
The models also produce their own such weather noise. It’s just that the noise within the models is not correlated in time with the real noise; getting that right would be like predicting the weather several years out. That is not the purpose. Their purpose is to get the longer term trends. Observations since 1998 are still within the model projection bounds, see https://www.realclimate.org/index.php/archives/2008/04/model-data-comparison-lesson-2/
I suggest you download the GISS Temp data and see for yourself how noisy the data are. Choose some random ten year periods, zoom in on them, and you’ll not always discern the longer trend. Then zoom out to a view of 40+ years, and you’ll see the trend pop out from the noise. Save some plots, and show them to your sceptic friends.
If I follow him, the author here is suggesting that recently there has been some longer-term coherence to the noise, in a sense – that the repercussions of that El Nino are still being felt, that we’ve been warmer than the mean trend since 1998, and that we’re only now coming back to the trend mean. I am unconvinced, but this post is already too long.
Douglas McClean says
If the ’97-’98 change is “better than 3 standard deviations of interannual variability” as you state, might that not simply indicate that the interannual variability is not normally distributed? Eyeballing the graph, it looks to me like changes of similar magnitude have occured downwards a half dozen times since 1900 and upwards perhaps 4. Would the actual year by year data put the lie to this eyeballing (perhaps some segments that look to me like one year might be two or three with near-matching slopes)?
Great blog, keep up the good work.
Timothy Chase says
Hank Roberts wrote in 8:
Hank, presumably it is official at this point.
But I would have to check to see whether this squares with the official definition.
As for what the models predict (as of 17 June 2009), you can see it here…
Summary of ENSO Model Forecasts
17 June 2009
… but things can change in a month’s time, and while the current El Niño is expected to last through Fall and Winter (and in fact roughly a year if it is typical), the previous one (early 2007, I believe) burned itself out unexpectedly and we fell back into a La Niña.
Has anybody tried to draw a connection between this work and the Keenlyside paper, which I believe used SST values for initialisation and predicted no warming for a while? Is there any plausible connection?
[Response: I think the connection is very intimate. We at RC think that some of the Keenlyside results “predicting” an interruption of warming were overstated and misinterpreted, but for me personally the take-away message from Keenlyside is that ocean dynamics is capable of producing a temporary warming interruption, even in the face of growing radiative forcing. –raypierre]
Also, what happens to the plots above if some other temp set is used, instead of Hadcru? I do wonder if we’re seeing artifacts of the chosen data set, particularly the one with selective exclusion of grid boxes.
Joel Shore says
Dr. Swanson: Another question – This prediction of a pause in the warming seems somewhat similar to the prediction of Keenlyside et al., although, as I understand it, theirs is based simply on a direct model prediction (with an attempt, whether successful or not, to use realistic initial conditions in initializing their model). Is it possible that they could be detecting in their model the sort of shift that you believe may have occurred…or do you think that the fact that they and you make a similar prediction may just be coincidence?
Joel Shore says
Brian Brademeyer (#14) says: “Look at the figure again. Looks to me like linear fit goes from -0.3 to +0.55 degrees in 50 years, or 0.17 degrees per decade.”
No, that’s from 1950 to 2030, which is a period of 80 years.
Jim Bouldin says
Thanks for the post Kyle. I hope you’re wrong though, because the thought of 10 more years of the deniers screaming (increasingly loudly) about how global warming is a bunch of not happening BS is a bit more than I for one can take. They could really use this to very damaging political advantage, weakening proactive action just when it’s most needed.
[Response: When the Keenlyside paper came out, Andy Revkin had a nice blog article on whether the drive for carbon mitigation action could survive a decadal interruption in warming. It’s a good question, but one I wouldn’t presume to know how to answer. Our best armory for the arguments you fear quite rightly is to build up our understanding of decadal variability and the extent to which it can cloud the long term trend. It’s too soon to say whether the current “pause” in warming is anything more than statistics being clouded by one unusual El Nino event, but we should be thinking now about possible explanations just in case something more interesting is going on. –raypierre]
Timothy Chase says
Greg Simpson wrote in 10:
Not exactly sure why you think that the forcings are accelerating. Methane seems to be picking up a bit, but then again, given the Asian Brown Cloud, so should the negative effects of reflective aerosols. Rate of percentage annual growth for carbon dioxide has certainly increased since the beginning of the 21st century, but this should result in a significant change in the rate of warming any more quickly than the differences between emission scenarios would, and there (according to the models) the differences aren’t significant for the first thirty-some years but progressively become more pronounced from then on — given the cummulative effects of accumulated carbon dioxide.
However, at least with NASA GISS, it would appear that there is no statistical basis as of yet to claim that the trend in warming has reversed itself, slowed or accelerated from what it was beginning in 1975.
January 31, 2008
However, I am sure that Tamino will appreciate the wavelet analysis and will be looking forward to hearing what he has to say.
wayne davidson says
#9, Thanks Dhogaza, I look forward to hear either from Raypierre or Dr Swanson.
I must add on, there are no reasons for the atmosphere as a whole not to warm, no active massive Volcano eruption neither extra sun reflecting aerosols, there is according to some a 1 W/m2 lull in solar forcing at this current solar minima. During an El-Nino episode, at least during this current one, there is cooling possible despite the heat exchanged from the ocean,
To state that a model or two foresees a lull in warming goes against my own powerful observations of expanding sun disks especially in the Arctic. I have not detected a consistent cooling in the Northern Hemisphere, nor does the temperature record show this, 2007 being the warmest year in history for the Northern Hemisphere (matching record year for Arctic Ocean ice shrinkage), 2008 and also 2009 despite having much cloudier Arctic summers show equally significant ice extent reductions. ENSO merely reflects a state of flux for the entire planetary climate system, of which La-Nina cools and El-Nino warms, but overall the temperature of the atmosphere is warming. As the coming months will show a significant warming for the temperature records.
1997 compared to 2009 seems adequate
January till May was warmer in 2009 despite La-Nina over past winter
as was in 1997 La-nina turned to El-Nino during summer.
So the evidence, if any about a temperature lull is not observed….
Brian Brademeyer says
You are right, it’s 80 years. Guess I need new glasses!
Geno Canto del Halcon says
It appears to me that if the HadCRUT3 data since 1980 were modeled with a least-squares analysis, assuming an exponential function, that it would likely model the data better than the green line for the period. If the data was somehow adjusted for changes in solar irradiance over the period, it might show an even stronger increase trend.
Erl Happ says
Based on past performance I would not expect this comment to get through moderation.
Hope springs eternal nonetheless.
The root cause of sea surface warming is a change in the intensity of solar radiation that reaches the surface of the ocean. There is no doubt that it is upper troposphere cloud that responds to change in local temperature in turn related to periodic change in ozone concentration that is in turn associated with vortex activity at the poles.
Verification is easy. Simply compare monthly anomalies in 20hPa temperature 10°N to 10°S with monthly anomalies in sea surface temperature at 20-30°S and 260-275°E (off the coast of Chile).
There has been a strong trend of declining 20hPa and SST since 1978 as the solar wind strength has fallen enabling a stronger flux of mesospheric nitrogen oxide into the stratosphere. Result is steady cooling. The trend to warming SST prior to 1980 is clearly related to a gradually warming stratosphere prior to that date.
Timothy Chase says
I find this approach interesting. Clearly there are teleconnections between the different climate modes, and it would certainly appear (as previous work along these lines would suggest) that the network of climate oscillations can undergo reorganization after they have entered a brief period of synchronization which marks the transition from one regime to the next.
However, as I understand it what is currently the mainstream view is that what explains the transition from early 20th century warming to the flat period between is the resumption of industrial production and thus of reflective aerosols (predominantly sulfates), and that likewise, it was the passage in the early seventies of laws requiring cleaner emissions that reduced reflective aerosols. Do you see the periods of synchronicity that mark the transitions between regimes as an alternative to this narrative — or as something that might complement it?
Additionally, if I am not mistaken, a “new” view that has become more or less mainstream is that chaotic systems are especially sensitive to forcing, such that anthropogenic forcing would “project itself… onto the modes of natural variability.”
Now if this were the case, changes in the forcing due to reflective aerosols at roughly the beginning of World War II and shortly after the enforcement of the Clean Air Laws in the developed economies might very well explain a transition from one climate mode regime to another — that is, if the climate system is particularly sensitive to changes in forcings. Would you see the approach you are presenting as in essence arguing that climate mode regimes are in fact more autonomous and that at least in the short-run, the climate system is more independent of forcings?
Doug Bostrom says
This is a very interesting post. I think what I’m hearing can be usefully be analogized to a familiar situation. We have an automobile with a defective cooling system, we’re descending a hill and seeing the temperature indicator stabilizing, but we can expect it to resume rising once we’ve back on the flats, or going up hill again. Is this a useful and halfway accurate way of thinking about it?
Jim Bouldin 12 Jul 2009 at 10:18 pm
[message of fear and loathing]
Jim, most of the things being proposed in the way of modernizing energy exploitation, capture and management are items that ought be high on a prioritized bullet list for improving the human and planetary condition regardless of what the climate situation is. Stabilizing hydrocarbon prices, preserving what liquid and gaseous hydrocarbon compounds we have available for better uses than combustion, encouraging conservation so as to save money, polluting less, the list goes on. Those are all tasks we need to complete so as to “build a better tomorrow” for reasons unrelated to our climate mess.
Some of the more “out there” ideas such as geoengineering become more difficult in an adverse policy climate, but those mostly have the common feature of being half-baked in any case and ought to be approached with extreme caution.
Regardless of what the factually challenged may believe, we should be doing most of what will be required for AGW reduction irrespective of the climate situation. Even if the impossible were to happen and we suddenly discovered that CO2 released in vast quantities were completely benign, we should be moving on from caveman energy habits. It’s incumbent on us to improve how we get energy and what we do with it, the sooner the better, or we’re going to have a more dismal future. That’s really not debatable for anybody with a reasonably broad perspective.
Frankly, it might be better to push improved energy technologies with climate mitigation being a second tier consideration in whatever pitch is required to capture imaginations and market share. Everybody likes predictable prices, everybody likes getting the same thing for less money; there’s nothing controversial about making things more predictable, less expensive.
Alex Harvey says
Dr. Swanson writes:
I am puzzled by this assumption that the “established pre-1998 trend is the true forced warming signal.” We have a trend that’s been fitted to the period 1979-1997 and shown to also fit the data reasonably well all the way back to 1850. That’s fine, and it seems that Dr. Shunichi Akasofu has made exactly the same point, except that the latter has attributed the same trend to recovery from the Little Ice Age rather than GHG forcing. And given that there wasn’t enough CO2 in the mid-nineteenth century to be causing the same warming as there was in 1975 it seems rather strange to me to be attributing a single linear trend all the way from 1850 until 1997 to GHGs without any mention of the warming trend that already existed in 1850. Has this analysis been simplified?
Edward Greisch says
“there are no guarantees to how the climate may respond. ”
“if the climate is not behaving as a linear forced”
“LINEAR” being the critical word. Several people mentioned wild departures from linear.
Reference: “With Speed And Violence” by Fred Pearce, 2007.
“The vanishing Face of Gaia” by James Lovelock, 2009, page 153 says that paleohistory shows a sudden 9 degree rise at 450 ppm equivalent. The physics is not stated. We are almost there.
If we had millions or billions of years of data equal to the data since the late 20th Century, of course you would already have figured out the non-linear equations that are really there. As it is, you can only try to fit linear equations to what you have. I’m glad somebody is using wavelets. The most powerful mathematics is clearly justified. What is really there that you have approximated as linear?
People like to make “easy” predictions, like sea level rise. Nobody wants to predict something hard, like when will agriculture fail in region X, or will I be able to afford dinner 2 years from now?
“humanity is poking a complex, nonlinear system with GHG forcing” and this is a dangerous thing to do.
Thank you for applying the most powerful math you can to try to figure out what the real equations are. We need to know yesterday.
Rob J says
“Also shown is a linear trend using temperatures over the period 1979-1997 (no cherry picking here…””
Unless you’re cherry picking a linear trend ?!
Samuel Watterson says
That was one of the best articles I’ve read here. Thank you. It will be interesting to see this tested in the coming years, unless some other unknown factor confuses us.
It would be good if Dr Swanson acted as tag team partner for Al Gore when GW denier Senator Steve Fielding presents Gore with ‘irrefutable’ evidence of cooling. Gore could step out of the ring for the heavy action.
Sure last Australian summer was cold at times and my pumpkins split with frost. There were also unprecedented bushfires and record high temperatures. Maybe the debate should not be politician vs politician.
In the Swanson and Tsonis paper it is suggested that the decadal variations of the global mean temperature, the climate shifts, observed in the 20th century are basically caused by the synchronization of four modes. I guess that the synchronization events occur by chance.
How is it then possible that the IPCC climate models can replicate these decadal variations at exactly the same years? For the wrong reasons?
“Raypierre, its completely counter intuitive to suggest that there will be a pause in Global Temperature warming.”
Read the fine article, Wayne.
if 1998 was an exceptional change, that change can make any nearby values exhibit a change that isn’t real, just the consequence of no longer having that exceptional change.
Look at the graph without the 1998 value. Nothing weird going on there.
It isn’t saying there’s a pause. In fact the article even says that it isn’t talking about a pause. It’s talking about a datapoint that is exceptional and how it can affect your perveption of what’s going on.
Note, for example, the slope of the green line. Without 1998, the mean fit slope doesn’t change much. But if you take only a small slice near that exceptional datapoint, you get huge variations.
If not, where were you in 1999 when the graph was pounding right through the roof? You weren’t yelling “THIS IS PROOF! AGW IS REAL!!!”. You kept strangely quiet.
“How do I answer the sceptics/deniers who utilise the cooling since 1998, matched with the trend lines in the IPCC reports that show warming climbing while the reality is cooling or at least flat lining?”
What you do is add up the last 10 years global mean. This period includes the “cooling” years and excludes the “hottest year” 1998.
You then compare that to the 10 years previous to that. This includes the warmest year and the warming that they describe as having reversed (in the last 10 years).
Compare the two.
The last 10 years, despite being “cooling” is about 0.2C warmer.
“If El Nino is put up as the reason why doesn’t the the forecast’s take that into account and show it???”
Because it’s a chaotic event. Like large volcanic eruptions or solare flares.
You can forecast what the average effect of such would be, but if it is big enough to show up on the global picture, you will see a deviation while it is in effect away from its average effect and later a deviation the other way.
“If the ‘97-’98 change is “better than 3 standard deviations of interannual variability” as you state, might that not simply indicate that the interannual variability is not normally distributed?”
Only if it happens significantly more than once every 100 ish years.
mauri pelto says
The coupling-decoupling mechanism and the means by which it is quantified seems sound. That all times of enhanced coupling would tend to cause a pause in the warming trend does not seem likely. Depending on the specific phases enhanced greater coupling should be able to enhance warming as we have seen with the phasing of PDO and el nino. The slow radiative dissipation argument does not seem plausible to me on the slow time scale indicated for such a short term event.
Lynn Vincentnathan says
Good I was in charge of the high school physics ripple tanks. I think that helps me understand this. You get bigger amplifications and troughs when the 2 ripples intersect…(I’m a bit fuzzy, but that’s what I recall from 45 yrs ago). By analogy, one ripple could be the natural variability, and the other, the forcing from GHGs. Then you add in other ripples from other aspects, and you could get whopper amplifications and troughs…..
Another thing I’ve been wondering for the past 20 yrs is that “episodes” such as el ninos might be getting stronger and/or more frequent due to global warming. (Or is the author also saying that?) In other words, not only does the micro/meso impact the macro climate level, but macro impacts the micro/meso climate/weather levels.
I vaguely remember that when I first learned about el nino over 40 yrs ago, they said they come about every 7 years. Timothy Chase (#18) says, “every two to five years.” Maybe my memory is wrong, or perhaps the science back then wouldn’t have been as advanced….
Also, I don’t know about that idea of record-breaking temps again resuming by 2020. Right now in the Rio Grande Valley we’ve been in record-breaking, above 100 F weather for several weeks, and the “cunecula” (heat wave that goes from July 14 thru the end of August) hasn’t even started yet. Houston got 114 a couple of weeks ago. I know, I know, single weather events don’t equal climate, but thought I’d balance out the claims of denialists in who say it’s cooler than usual in their area.
Alastair McDonald says
Dear Dr Swanson,
I am puzzled. You identify three episodes (during the 1910’s, 1940’s, and 1970’s), with the 2000’s as presumably the fourth, yet you draw a trend line through 1950 to 2000. Shouldn’t each episode have a separate trend line?
Either we have a dynamical system as you claim in your paper, or the system is linear as you infer with your straight trend line. Which is it?
From the fine article:
“Shouldn’t each episode have a separate trend line?”
No, because the 1910’s, etc are all proofs that saying “this decade is showing a low trend” means nothing. This has happened many times in the past, yet rather than getting back to what was had before this “cooling!” we have temperatures higher than before.
So saying “this last 10 years has a trend much lower” means nothing since the same has happened before and yet we are still much higher at this lower ebb than any time before 1979 (IIRC). Even those years showing a peak.
“You get bigger amplifications and troughs when the 2 ripples intersect…(I’m a bit fuzzy, but that’s what I recall from 45 yrs ago). By analogy, one ripple could be the natural variability, and the other, the forcing from GHGs. Then you add in other ripples from other aspects, and you could get whopper amplifications and troughs…..”
Constructive interference was done in Physics when I was 14.
Is it no longer done???
Phil. Felton says
Dr. Shunichi Akasofu has made exactly the same point, except that the latter has attributed the same trend to recovery from the Little Ice Age rather than GHG forcing.
And what caused that ‘recovery’?
[Response: Yes, this points up a common misconception about the operation of climate. Though we speak of “thermal inertia,” it’s not really inertia in the sense of Newtonian mechanics. If you start a warming trend by increasing a climate warming forcing and then zeroing it out, it does not (unlike a body in notion) tend to keep on warming unless you do something later to stop it. Warming is a damped response to the current forcing, and the minute you zero out the forcing, the trend will turn the other way. “Committed warming” is only committed because the scenario there is not zeroing out the GHG forcing, but rather freezing its value, giving the climate time to catch up. In this sense, the dynamics of climate change is more Aristotelian than Newtonian. –raypierre]
“That all times of enhanced coupling would tend to cause a pause in the warming trend does not seem likely.”
An exceptionally strong El Nino brings no *new* energy into the system. What it does is change the location of it and makes it easier to spot (to an extent). But that doesn’t make any more energy in the system if nothing else happened to force a change.
Therefore it’s likely that any discourse to the other side in the subsequent period will have changed.
E.g. El Nino keeps warm water at the surface longer. Therefore what would have gone down into deeper ocean is kept nearer the surface. Then the next La Nina has not had the benefit of that introduction of that energy it would normally have. And it hasn’t had enough time to even this out by drawing energy from other places (which it could do for later La Nina). Therefore a greater cooling because the deep water didn’t get the warmth a more normal El Nino would have let it take.
PS I can never remember which way round it goes El Nino warming? I’ve seen it plenty times, but it just doesn’t seem to stick.
Timothy Chase :
12 Jul 2009 at 10:01 pm:
I think you mean early 2008. In early 2007 the various ENSO metrics were all dropping as what turned out to be the 2007-2008 La Nina emerged. It’s true that things change unexpectedly over a month’s time, but July is during the time of year when rapid changes in the ENSO state are less common, while the one that ‘burned out’, which I think you refer to, ‘burned out’ earlier in the year when such reversals are more common.
See pg 26 (or 22) of this ENSO status and evolution report. The most recent ONI value (April – June) of 0.2 is greater than the peak ONI value of 0.0 reached in early 2008, when the 2007-2008 La Nina ended. (Note that whether the Pacific went back into La Nina is debatable; the NOAA official metric requires at least 5 consecutive overlapping 3 months periods with ONI less than or equal to -0.5 . Following early 2008, there were only 4 overlapping 3 month periods of ONI equal to or below -0.5, as you can see on pg 26.) (See here for a different (MEI) metric which tells a similar story.)
43, OK, I used the wrong word.
“Raypierre, its completely counter intuitive to suggest that there will be a pause in Global Temperature warming. ”
It isn’t a pause in global warming trend (GT Warming) which you need more than 10 years (around 30 will do fine) but a drift from the trend (which CAN be seen in 10 years, if barely) that added to the trend which hasn’t paused and gives an *appearance* of the climate (30 year) trend of having stopped.
It would take another 2 10-year periods to prove the climate trend having stopped.
At least that’s the difference I got from Wayne’s post about the article and the article itself.
Chris Dudley says
Much ado, yes, but what about? The idea that the inter-annual change between 1997 and 1998 is anomalous needs more support. First, is it really three standard deviations? What if the year definition is phase shifted by six months? If it is 3 standard deviations, why would that be an anomaly? With enough data, the absence of any points at three standard deviations would be the curiosity, indicating a non-normal distribution, rather than their presence.
It seems to me that the rise is marked by a real physical event, El Nino, rather than its statistical rank in a larger record, and the stronger statement is that even the largest “variability” events can’t hold a candle to the long term trend of temperature increase. They are down in (or are) the noise.
In any case, it seems to me that it is quite difficult to identify a “break” in the mean temperature trend from the date shown here and even more so from the GISS data, mentioned but not shown. So, it is hard to base a paper on that.