Tamino (aka Grant Foster) will have his knickers in a twist over this one.
Guest post by Marcel Crok (from his blog De staat van het klimaat)
An interesting new paper (behind paywall) has been accepted for publication in the Journal of the Atmospheric Sciences. The paper by Jiansong Zhou and Ka-Kit Tung of the University of Washington, Seattle is titled “Deducing Multi-decadal Anthropogenic Global Warming Trends Using Multiple Regression Analysis”.
This paper will add fuel to the recent discussions about the nature of the global warming trend and whether it recently has stabilized or not. The authors by the way conclude it has not. Their main conclusions however is:
When the AMO is included, in addition to the other explanatory variables such as ENSO, volcano and solar influences commonly included in the multiple linear regression analysis, the recent 50-year and 32-year anthropogenic warming trends are reduced by a factor of at least two. There is no statistical evidence of a recent slow-down of global warming, nor is there evidence of accelerated warming since the mid-20th century.
This study is following the same approach as Foster/Rahmstorf 2011 and Lean/Rind 2008 (trying to correct the global temperature for ENSO, solar and volcanoes) but adds the Atlantic Multidecadal Oscillation to their multiple linear regression analysis. This leads to their figure 1b above. What we see is a longterm trend that has hardly changed during the past century.
Now as always this result can be interpreted in many different ways. The century scale trend is still 0.68 degrees Celsius suggesting little of the total trend of 0.8 degrees C can be attributed to solar, volcanic, ENSO and AMO. That’s what the authors seem to suggest as well when they write (bold mine):
The conclusion that we can draw is that for the past 100 years, the net anthropogenic trend has been steady at approximately 0.08 °C/decade.
So for them anything that’s left after filtering out the natural forcings and natural variability is just ‘anthropogenic’. For me this conclusion is rather premature. But before I explain why let’s focus on the other trend lines that the authors show. Just like Foster/Rahmstorf they conclude that there is no slowdown recently:
There is no statistical evidence of a recent slow-down of global warming
However the trend they find for the recent 32 years (0.07ºC/decade) is far lower than that of Foster/Rahmstorf (0.17ºC/decade). If the approach has any validity at all this would suggest that the AMO alone explains the difference between the Zhou/Tung and Foster/Rahmstorf trend.
The paper by Zhou claims that in the last 32 years, the period in which greenhouse gases are supposed to be the dominant forcings, in fact some 60% (0.1ºC of the total 0.17ºC/decade) of the trend can be ‘explained’ by a combination of ENSO, AMO, solar and volcanic forcing). Ergo, only 40% of the trend could be attributed to other factors among which greenhouse gases are of course a logical candidate.
However there are other candidates as well of course. There is ongoing debate about the influence of siting issues on the temperature measurements on land as well as the Urban Heat Island effect and other socio-economic influences. In a controversial and well known paper Michaels/McKitrick estimated that “Using the regression model to filter the extraneous, nonclimatic effects reduces the estimated 1980–2002 global average temperature trend over land by about half.” If true even less of the remaining trend can be attributed to greenhouse gases.
The Zhou study could therefore have serious implications for our estimates of climate sensitivity. The paper though is completely silent about these potential implications, something that reviewers could have raised.
As said above Zhou and Tung call the remaining century long ‘underlying’ trend ‘anthropogenic’. Whether this is ‘right’ could be questioned with their figure 2 (see below). Here one sees that the anthropogenic forcing (green line) seems to underestimate the adjusted trend in the period (1889-1970) while it seems to overestimate the trend thereafter. This suggests that still not all the relevant factors (either natural or anthropogenic forcings or natural variability) are included in the regression analysis. The residuals in figure 2b still show trends which would not be the case, Zhou and Tung write, if the regression analysis would be perfect.
This leaves enough room for all to bend the paper in one’s preferred direction.
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Deducing Multi-decadal Anthropogenic Global Warming Trends Using Multiple Regression Analysis
| Abstract |
|---|
In order to unmask the anthropogenic global warming trend imbedded in the climate data, multiple linear regression analysis is often employed to filter out short-term fluctuations caused by El Nino-Southern Oscillation (ENSO), volcano aerosols and solar forcing. These fluctuations are unimportant as far as their impact on the deduced multidecadal anthropogenic trends is concerned: ENSO and volcano aerosols have very little multi-decadal trend. Solar variations do have a secular trend, but it is very small and uncertain. What is important, but is left out of all multiple regression analysis of global warming so far, is a long-perioded oscillation called the Atlantic Multi-decadal Oscillation (AMO). When the AMO Index is included as a regressor (i.e. explanatory variable), the deduced multi-decadal anthropogenic global warming trend is so impacted that previously deduced anthropogenic warming rates need to be substantially revised. The deduced net anthropogenic global warming trend has been remarkably steady and statistically significant for the past 100 years.
Since the AMO trend (or North Atlantic SST record) for 1910-1945 and 1975-2005 is exactly the same, I do not get from where they got those 40 and 60%.
Why do they split the trend at 1970?
A linear trend is a model. If after 1970 a new model is required the only possible reason is the increasing influence of antropogenic greenhouse gases. But then, calling the trend for the previous period an “antropogenic” trend is inexplicable. And all that the added greenhouse gas accumulation would cause is the difference in slope between the two trends, about 0.15 deg C in 40 years or 0.0375 deg C/decade.
The Zhou study could therefore have serious implications for our estimates of climate sensitivity. The paper though is completely silent about these potential implications, something that reviewers could have raised.
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The paper is likely silent on purpose. To avoid the firestorm of controversy that would have resulted if they were to questions the orthodoxy. Such an action, to questions scientific beliefs, is to commit scientific heresy. The punishment is to have ones career burned at the stake.
Natural oscillations in the North and the South hemispheres run out of phase. To do a proper job two should be treated separately, and then recombine to observe the global change, but I suggest it would be preferable to present separate graphs first.
This sort of thing reminds me of papers on naturopathy. The herb is first assumed to be therapeutic, the experiment shows an elevated level of some molecule in the bloodstream, and the conclusion of the paper is that the elevated level must cause the therapeutic effect. There is not much difference with saying that the reason our curves don’t overlay perfectly must be AGW.
It starts with HADCRUT4. It doesn’t really matter how much infinitesimal meaning they can squeeze out of that, because they start with HADCRUT4.
This paper appears to make the same blatantly obvious error as Foster and Rahmstorf (2011). It assumes the effects of ENSO can be removed from the instrument temperature record through linear regression. They cannot.
http://bobtisdale.wordpress.com/2012/01/14/revised-post-on-foster-and-rahmstorf-2011/
It also fails to account for the very obvious long-term impact of ENSO on the sea surface temperatures of the North Atlantic. Note how the detrended North Atlantic sea surface temperature anomalies do not cool fully during the La Nina events that follow the El Nino events of 1986/87/88 and 1997/98:
http://i48.tinypic.com/ndldht.jpg
Boooh! No more research funds for you… 😉 Sorry, I couldn’t resist.
How did they account for UHI when determining the anthropogentc warming signal? Land use changes from human activity are not properly taken into account.
The AMO is defined as a linearly detrended North Atlantic sea surface temperature (SST). See the AMO index page at http://www.esrl.noaa.gov/psd/data/timeseries/AMO/
Subtract regional temperature (affected by solar, volcanic, ENSO variations) from global temperature (affected by solar, volcanic, ENSO variations), and amazingly enough your signal goes away. The differences are quite small – http://tamino.wordpress.com/2011/01/30/amo/
It will be very interesting to see what their regression coefficients are like – my suspicion is that the AMO will dominate as highly correlated, as changes in the AMO index are driven by those same solar, volcanic, and ENSO effects, and will encompass them.
Matt Skaggs says:
October 17, 2012 at 7:33 am
Pedantic rant:
A molecule is an assemblage of atoms. In this context, for a molecule to be elevated implies a place, e.g. in the head rather than the foot.
An elevated level of some chemical implies a greater number of molecules in one sample versus another.
“Chemical” has been added to the non-politically correct view of the world reserved for horrible pollutants like carbon dioxide. Personally, I like to think I’m full of chemicals, though I confess I have more molecules than chemicals. Chemistry is like that….
Solar, ENSO, AMO and volcanic signals have been removed, dropping the total in half.
The CAGW IPCC narrative says that these other influences are not significant, or less than about 25% (from the leeway I see they give themselves). The paper challenges the assumptions, not the record.
The CAGW enthusiasts would argue that this paper doesn’t change a thing about their stride to reduce fossil fuels. It is the total thermal impact of man and nature that counts. Man can only moderate his part, and with that part moderated or removed, the temperature rise comes to not be “catastrophic”.
So this paper could be used to support the Gore-Hansen-Suzuki screed: take the “known” elements out of his study, and man must be the problem!
According to my findings the AMO (9-10yr) is driven by difference in the phase between solar oscillations and the Earth’s magnetic ripple.
http://www.vukcevic.talktalk.net/EarthNV.htm
A similar process may be driving the ENSO (4.5-5yr) but with near double frequency,
http://www.vukcevic.talktalk.net/ENSO.htm
The AMO is by far more dominant in the N. Hemisphere.
Both oscillations have much longer period component.
Including the AMO as an explanatory variable is a mistake. My own work indicates that global temperature Granger-causes the AMO, not the other way around. Their regression is spurious.
The authors’ conclusion:
If the residual trend has been remarkably steady for the past 100 years that is proof that it is NOT anthropogenic.
Can’t be sure without access to the full paper, but it sure LOOKS as if they did not include GHGs in their regression analysis:
What the hell? That’s not legitimate in the least. Their “regression” does not include the what they are contending is pointed to as the main explanatory variable. As a result, we have no idea from their analysis how much explanatory power GHGs have and how much residual or “unexplained” error there would be.
Crazy. And from the link I see that Forster and Rahmstorf did the same thing. In my field of economics regression analyses are done all the time and I can guarantee that no economist would ever even conceive of the idea of not including their proposed explanatory variable in a regression. That’s the whole point: to get a statistical measure of the explanatory power of the variables one is looking at. Maybe if CO2 data were not available you would try to estimate its explanatory power indirectly by controlling for other variables, but CO2 data IS available.
I think we can be certain that they did run their regression with CO2 included and just aren’t showing us the results. After all, It’s a matter of a few minutes work to pull up a CO2 time series and add it to the regression. Here, I’ll time myself, starting at 10:45AM PDT. Law Dome, 10:46 AM PDT:
http://www.ncdc.noaa.gov/paleo/metadata/noaa-icecore-2455.html
So the authors definitely ran the regression with CO2. They just don’t want to show us how the residual error from their published regression gets divided between unexplained error and an estimate of the explanatory power of CO2, instead pretending that unexplained error IS the estimated explanatory power of CO2.
Can FOIA be used to prove that they did in fact run the regression with CO2? If so, I think this would be a proven case of scientific fraud. These guys are at the University of Washington so maybe it’s doable. But before I go too far with this accusation, maybe post-author Marcel Crok can give us some more detail on what is in the pay-walled paper. Is the impression from the abstract correct? Have they really left GHGs out of their regression? If so, do they offer any rationale?
Yet another regression. An interesting one, but that doesn’t make it right. I don’t think it’s significantly different from many other regressions I have seen so far, including those made to “feed” climate models.
The “anthropogenic forcing” regression is clearly regression to CO2 concentrations, hence the shape. Reduced portion of CO2 influence on climate may be due to last 16 years of warming “stall” because that made the regression to favor natural cycles more than in earlier regressions made for models when this stall wasn’t there.
I don’t wonder they don’t mention implications on climate sensitivity – it would sure make the review process a whole lot more complicated.
Barton Paul Levenson says:
October 17, 2012 at 10:54 am
Including the AMO as an explanatory variable is a mistake. My own work indicates that global that global temperature Granger-causes the AMO, not the other way around. Their regression is spurious.
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What causes “global temperature” to go in 50 year up and down cycles then?
You’re right back at north Atlantic ocean cycles then.
Don’t think they include the slow rise in temperature due to recovery from Little Ice Age, or the very long-term effects of the deep Thermohaline ocean currents which could be warmer now following the MWP heating event, May also be other omissions?
The paper is weak as it fails to include all climate drivers and its conclusions are, therefore, less than convincing. I can give this one a ‘C’ at best.
Here is my own model of Hadcrut4 on a monthly basis (versus annual that this paper uses I assume).
Too close to be a fluke – and my warming rate is only 0.045C per decade on a linear rate (although 2.0*Ln(CO2) provides a closer fit or 1.3C per CO2 doubling)
http://s19.postimage.org/gg5zqvvrn/Hadcrut4_Model_Aug_2012.png
60% are they kidding, it is just about 100%, co2 having 0% effect on the climate, which wil be proven before this decade ends.
this paper is useless more or less, even though it sides against co2 but it is hedging all over the place and doesnot adress why the climate changes and how, which I do ,which will be on my web-site in the very near future.
This paper like almost evey other single paper wants a silver bullet. Now it is the AMO,tomorrow it will be the PDO, then it will be volcanic eruptions, then it will be the thermohalinec circulation.
No concept as usual, that in order to understand the climate one has to take a major comprehensive approach to the subject, this kind of an approach is a waste of time.
I am done.
This is another typically useles IPCC type paper which ab inito assumes “Solar variations do have a secular trend, but it is very small and uncertain.” There is no reason to read any further than that statement. before safely ignoring the rest.
“regression analysis is often employed to filter out short-term fluctuations” … It would seem to me that most of our weather and climate are made up of short term fluctuations, to discount them is like putting blinders on. If the volcano didn’t happen, if the Ocean fluctuation didn’t exist. .. Instead of figuring out why they exist science picks and chooses what it wants to include. Blinders with a carrot in front . . . that’s what that is.
These kind of studies make me want to scream. I am really to upset to write anything of significance right now. Of course they believe in AGW, that is why the whole thing is ridiculous. Idiots!