Rethinking Climate Sensitivity: Roy Spencer Speaks
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:
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.