The Holy Grail of climate change is a quantity known as the climate sensitivity—that is, how much the average global surface temperature will change from a doubling of the atmospheric carbon dioxide concentration. If we knew this number, we would have a much better idea of what, climatologically, was headed our way in the future and could make plans accordingly.
Thus far, however, this prize has been elusive. Back in 1990, in its very first Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) suggested that the climate sensitivity was somewhere between 1.5°C to 4.5°C. In its latest Fourth Assessment Report published in 2007, the IPCC said the climate sensitivity was likely to be between 2.0°C and 4.5°C, and unlikely be to less than 1.5°C. Not a whole heck of a lot more certain than where things stood 20 years ago—and this despite a veritable scientific crusade to determine a more precise value.
A predominant member of the quest is the University of Alabama in Huntsville’s Dr. Roy Spencer. Dr. Spencer has, for several years now, been trying to untangle climate feedbacks from climate forcings. If apparent feedbacks are really forcings, or vice versa, then the determination of climate sensitivity is confused and prone to being wrong (and likely erring on the high side).
Dr. Spencer has long held that what has generally been taken to be a positive feedback from cloud cover changes in response to climate warming (i.e. cloud changes act to further enhance a CO2-induced warming) is actually the other way around—random cloud cover changes force temperature changes. However, trying to demonstrate that this is the case has proven challenging, and trying to convince the general climate community has been virtually impossible.
To help bring his ideas to a wider audience, Dr. Spencer has written a book about his hypothesis and his research in support of it, and has now, after years of tireless pursuit, published a paper in the peer-reviewed scientific literature.
Realizing that his findings run counter to the extant mainstream view of things, he has taken the step to ask for “physical scientists everywhere” to try to debunk his ideas. The appeal for scrutiny is intended to serve both science and Dr. Spencer in helping to solidify and illuminate a potential new way forward to finding the elusive Grail.
Recently, Dr. Spencer has written a nice summary of his on-going research and what, in his views are its implications. Rather than having me rehash his synopsis, Dr. Spencer has graciously permitted us to reprint a piece that originally appeared on his excellent website (a site well-worth checking from time to time).
Hopefully, readers of MasterResource will find this cutting-edge climate research interesting, and I am sure that if any of you have any pertinent suggestions for Dr. Spencer regarding his work, he would be happy to hear them.
Here is the excerpt:
Our JGR Paper on Feedbacks is Published
Roy W. Spencer, Ph. D.
After years of re-submissions and re-writes — always to accommodate a single hostile reviewer — our latest paper on feedbacks has finally been published by Journal of Geophysical Research (JGR).
Entitled “On the Diagnosis of Feedback in the Presence of Unknown Radiative Forcing“, this paper puts meat on the central claim of my most recent book: that climate researchers have mixed up cause and effect when observing cloud and temperature changes. As a result, the climate system has given the illusion of positive cloud feedback.
Positive cloud feedback amplifies global warming in all the climate models now used by the IPCC to forecast global warming. But if cloud feedback is sufficiently negative, then manmade global warming becomes a non-issue.
While the paper does not actually use the words “cause” or “effect”, this accurately describes the basic issue, and is how I talk about the issue in the book. I wrote the book because I found that non-specialists understood cause-versus-effect better than the climate experts did!
This paper supersedes our previous Journal of Climate paper, entitled “Potential Biases in Feedback Diagnosis from Observational Data: A Simple Model Demonstration“, which I now believe did not adequately demonstrate the existence of a problem in diagnosing feedbacks in the climate system.
The new article shows much more evidence to support the case: from satellite data, a simple climate model, and from the IPCC AR4 climate models themselves.
Back to the Basics
Interestingly, in order to convince the reviewers of what I was claiming, I had to go back to the very basics of forcing versus feedback to illustrate the mistakes researchers have perpetuated when trying to describe how one can supposedly measure feedbacks in observational data.
Researchers traditionally invoke the hypothetical case of an instantaneous doubling of the CO2 concentration of the atmosphere (2XCO2). That doubling then causes warming, and the warming then causes radiative feedback which acts to either reducing the warming (negative feedback) or amplify the warming (positive feedback). With this hypothetical, idealized 2XCO2 case you can compare the time histories of the resulting warming to the resulting changes in the Earth’s radiative budget, and you can indeed extract an accurate estimate of the feedback.
The trouble is that this hypothetical case has nothing to do with the real world, and can totally mislead us when trying to diagnose feedbacks in the real climate system. This is the first thing we demonstrate in the new paper. In the real world, there are always changes in cloud cover (albedo) occurring, which is a forcing. And that “internal radiative forcing” (our term) is what gives the illusion of positive feedback. In fact, feedback in response to internal radiative forcing cannot even be measured. It is drowned out by the forcing itself.
Feedback in the Real World
As we show in the new paper, the only clear signal of feedback we ever find in the global average satellite data is strongly negative, around 6 Watts per sq. meter per degree C. If this was the feedback operating on the long-term warming from increasing CO2, it would result in only 0.6 deg. C of warming from 2XCO2. (Since we have already experienced this level of warming, it raises the issue of whether some portion — maybe even a majority — of past warming is from natural, rather than anthropogenic, causes.)
Unfortunately, there is no way I have found to demonstrate that this strongly negative feedback is actually occurring on the long time scales involved in anthropogenic global warming. At this point, I think that belief in the high climate sensitivity (positive feedbacks) in the current crop of climate models is a matter of faith, not unbiased science. The models are infinitely adjustable, and modelers stop adjusting when they get model behavior that reinforces their pre-conceived notions.
They aren’t necessarily wrong — just not very thorough in terms of exploring alternative hypotheses. Or maybe they have explored those, and just don’t want to show the rest of the world the results.
Our next paper will do a direct apples-to-apples comparison between the satellite-based feedbacks and the IPCC model-diagnosed feedbacks from year-to-year climate variability. Preliminary indications are that the satellite results are outside the envelope of all the IPCC models.
Dr. Spencer is straining to construct a case for the possibility of low climate sensitivity, in spite of abundant evidence (from the paleoclimate record, from the climate response to solar variability, and from the record of twentieth century climate change) that sensitivity is in range of 2 – 4 degrees C per doubling of CO2. His “model” requires not only that clouds & water vapor act as a highly effective negative feedback mechanism, reacting strongly to global average surface temperature so as to regulate climate, but also that clouds and water vapor have large (and unobserved) random fluctuations that just happen to have occurred in such a way as to cause the 20th century warming.
His claim that climate science has not considered the possibility of low sensitivity is simply false. Studies such as the climateprediction.net project have explicitly attempted to explain the observed record using low-sensitivity models, and failed.
Have we had any decades where the alleged anthropogenic warming was on a trend to be above, say, 1.5C for 2x?
It seems to me to be a question of discovering why real-world warming in less than what high-sensitivity models predict.
The biggest issue I have with the theory of CO2 being the dominant factor in climate change, is that it is such a small part of the atmosphere in the first instance. I am wondering whether any physicists have ever looked at 390 ppm of CO2 in the atmosphere, and made any consideration as to how it could physically retain heat in the atmosphere at those levels
After that, since the human or anthropogenic contribution to the CO2 component in the atmosphere is somewhere between 3-4%, how do we make a significant contribution to climate change, or even changing it, when we only have influence over ~12ppm of the CO2 fraction in the atmosphere?
Most scientific discourse on this issue has revolved around the acceptance that relatively low amounts of CO2 can physically vary the heat exchange attributes of the atmnosphere, and that humans are responsible for a significant portion of the CO2 in the atmosphere. Neither of these propositions have ever been proven in my view, which of course cast much doubt on the viability of the forecast of the feedback mechanisms and subsequent climate sensitivity.
[…] of various influencing factors (e.g. clouds). This is a good discussion on part of that <<http://www.masterresource.org/2010/09/quest-for-climate-sensitivity-spencer/>>. “Say Goodby To Sunspots” is about an alternate theory to AGW […]
Why does there have to be climate sensitivity to CO2? I understand deserts show no evidence of warming let alone alarming warming in the absence of water vapour. Have they been cooling and CO2 has offset the cooling? I can’t think of any other explanation if CO2 really is the miracle gas claimed by so many.
I saw mention of this recent journal article:
Christy, J.R., Herman, B., Pielke Sr., R., Klotzbach, P., McNider, R.T., Hnilo, J.J., Spencer, R.W., Chase, T., and Douglass, D. 2010. What do observational datasets say about modeled troposphere temperature trends since 1979? Remote Sensing 2: 2148-2169.
rbradley, regarding the purported effect if CO2 at 390 ppm, what matters is how much longwave thermal radiation form the earth’s surface is absorbed by that CO2. The top of atmosphere satellites show that a healthy chunk of the earth’s outgoing radiation is absorbed by the CO2. What matters is the absorptivity of the gas, and the width of its absorption band. Methane, if it were present in the atmosphere at the same concentration as CO2 would absorb 25 times more outgoing thermal radiation than does CO2. The amount of the gas is not the relevant issue, only the light absorbing power.
RBradley, I agree with your assertion that “a healthy chunk of the earth’s outgoing radiation is absorbed by the CO2” but counter with the fact that it is the sum of all LW radiation absorbed and all radiation that escapes that is important, not isolated bands. The fact is recent measurements show increased amounts of LW being emitted to space that more than offset increased absorption in CO2’s slender absorption bands.
Warmists contend that the surface layer has warmed due to CO2 remitting towards the surface. I don’t believe this is possible because upward radiated CO2 is absorbed within ~30 mtrs almost to extinction (converted to other energy forms or longer wavelengths), that suggests to me that downward radiation meets a similar fate.
I suggest that WV and ice crystals moving from the stratosphere downward have increased lower tropospheric humidity that is surely short term due to the decrease in supply provided by UV driven evaporation that has been diminished by ozone recovery.
What say you sir.
(Apologies for the delay in replying)
[…] to CO2 and/or the feedback effect of temperature increases on water vapour levels (See Roy Spencer here). Sea level rises were probably overstated, as it was assumed that Antarctic temperatures would […]