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.
======================================================
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.
Nicola Scafetta, I think we are on the same page as far as solar effects go on the climate, where the difference lies is you think AGW effects are present and I don’t, which gives the different temperature outlook.
That is what it is, as far as I can determine.
Also you are not accounting fro possible thresholds which could come about,(i am not saying they will ,but they could) which would change everything.
Salvatore — Talking about thresholds see http://www.sciencemag.org/content/337/6095/704.figures-only
note especially fig one.
Here is link to abstract
http://www.sciencemag.org/content/337/6095/704.abstract
Here is abstract
Earth’s climate underwent a fundamental change between 1250 and 700 thousand years ago, the mid-Pleistocene transition (MPT), when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing. Over this time, an increase occurred in the amplitude of change of deep-ocean foraminiferal oxygen isotopic ratios, traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep-ocean temperature. We have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios. Our results suggest that the MPT was initiated by an abrupt increase in Antarctic ice volume 900 thousand years ago. We see no evidence of a pattern of gradual cooling, but near-freezing temperatures occur at every glacial maximum.
Another great paper relating to solar change.
http://icecap.us/images/uploads/abduss_APR.pdf
Abstract
Temporal changes in the power of the longwave radiation of the system Earth-atmosphere emitted to space
always lag behind changes in the power of absorbed solar radiation due to slow change of its enthalpy. That is
why the debit and credit parts of the average annual energy budget of the terrestrial globe with its air and water
envelope are practically always in an unbalanced state. Average annual balance of the thermal budget of the
system Earth-atmosphere during long time period will reliably determine the course and value of both an energy
excess accumulated by the Earth or the energy deficit in the thermal budget which, with account for data of the
TSI forecast, can define and predict well in advance the direction and amplitude of the forthcoming climate
changes. From early 90s we observe bicentennial decrease in both the TSI and the portion of its energy absorbed
by the Earth. The Earth as a planet will henceforward have negative balance in the energy budget which will
result in the temperature drop in approximately 2014. Due to increase of albedo and decrease of the greenhouse
gases atmospheric concentration the absorbed portion of solar energy and the influence of the greenhouse effect
will additionally decline. The influence of the consecutive chain of feedback effects which can lead to additional
drop of temperature will surpass the influence of the TSI decrease. The onset of the deep bicentennial minimum
of TSI is expected in 2042±11, that of the 19th Little Ice Age in the past 7500 years – in 2055
Dr. Abdossamatov, is also correct. I am thinking 2014 or so.
The question is will any thresholds be met, I mean actual thresholds? I don’t know if I can answer my own question, but I do know they are out there for some given values of solar activity changes,along with earth magnetic field changes. They are out there.
But no two situations will always be the same ,so that different outcomes will be the rule even if various forcings are the same because the climate system is non linear, that is what makes it 1000x harder.
One thing I do know is that the chances of something major have not been this high since the Dalton Minimum.High being relative to years prior to 2005, which presented a zero chance of something major, I say we have a 5% chance now.
I think its more than that – at least 50% go to
http://solarcycle24com.proboards.com/index.cgi?board=general&action=display&thread=855&page=47
and read through the Livingston and Penn thread
You may be correct.
S de P: An upper warmer level of air , will not warm a lower level. Unless you want to change the second law of thermodynamics, which won’t surprise me since the AGW side will do anything to prove there obsolete points.
BPL: Sure it will. There’s no violation of the laws of thermodynamics. What makes you think there is?
Not sure WHO will have his knickers in a twist on this paper, but certainly not Tamino.
This paper by Zhou and Tung is classic case of ‘extreme’ “contamination” in regression analysis.
When you want to remove a known variation in a climate forcing from the global temperature record, you always have to be very careful not to mix cause and effect. After all, if your ‘forcing’ contains a global warming signal, then that too will be eliminated from the global warming record !
In extreme cases, if your ‘forcing’ (cause) mainly consists of the global warming signal itself (effect), then you end up with a flat line. If you subtract a trend line from your forcing, you end up with a trend line. And that is exactly what happened in the case of Zhou and Tung.
The global temperature signal is VERY strong in the AMO index they used :
Check the Northern Atlantic SST record against the global temperature record here :
http://tamino.files.wordpress.com/2011/01/sst_giss.jpg
These two records are clearly highly correlated (anyone want to determine the R^2 on this?).
So, when Zhou and Tung ran their regressions to eliminate their AMO index, they eliminated not just some minor Atlantic SST anomalies, but also most of the global temperature record from the global temperature record. So, they were left over with mostly the trend line in the Northern Atlantic SST record. And remember that that is the trend line was removed BY DEFINITION to obtain their AMO index.
Also it is not as if the trap (of contamination due to mixing up cause and effect) that Zhou and Tung fell right into is new or unknown in the field of climate science.
In fact, there have been dozens of papers pointing out the problems with contamination in multi-regression analysis, and specifically to the AMO, attempt to avoid the problems, and including methods to avoid it date way back :
For example, Mann and Park, 1994 discuss the issue and propose a multivariate signal detection procedures to tease oscillatory patterns apart from long-term (potentially non-linear) trends. Or Schlesinger and Ramankutty, 1994 who use climate model-based estimates of forced trends to estimate a possible residual oscillatory component instead of linear trends.
And then Meehl et al., 2004; Barnett et al., 2005; Hansen et al., 2005 all mention that to properly deal with purely Atlantic variability, it is highly desirable to remove the larger-scale global signal that is associated with global processes, and is thus related to global warming in recent decades, from the AMO.
Also, Trenberth and Shea, 2006 clearly explains the problem of global warming signal being present in the NA SSTs, and suggests a “alternative AMO” definition that at the very least subtracts the global SSTs from the Northern Atlantic SST record (similar to my Tamino’s suggestion to subtract GISS, but probably global SST is better, since it deals with ocean temperatures).
Needless to say that Zhou and Tung’s conclusions that “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.” as well as “the net anthropogenic trend has been steady at approximately 0.08 °C/decade”, as well as Marcel’s title of this post are incorrect and artificially created by Zhou and Tung defining the AMO as “linearly detrended”.
You are simply looking at the 100 year linear trend line in the global temperature record, which is indeed something like 0.08 C/decade.
Now, if I (as an amateur) can see that there is a problem with this paper in 10 minutes, and an hour to recognize what the problem is, and a couple of hours to find out the background and prior work on this issue, I wonder why was Dr. Tung, with 30 years of experience in this field, not able to do so ?
Oh.And did I forget to mention that Dr. Tung is a student of Dr. Lindzen, and the Chief editor of the journal in which this paper was published ?