Major Science study: Observations confirm “the short-term cloud feedback is likely positive”
Trenberth explains, "The work is sound and is a very useful contribution," while Roy Spencer makes an unsound response.
December 9, 2010
Changes in clouds will amplify the warming of the planet due to human activities, according to a breakthrough study by a Texas A&M University researcher.
Andrew Dessler, a professor in the Department of Atmospheric Sciences, says that warming due to increases in greenhouse gases will cause clouds to trap more heat, which will lead to additional warming. This process is known as the “cloud feedback” and is predicted to be responsible for a significant portion of the warming over the next century….
“I think we can be pretty confident that temperatures will rise by several degrees Celsius over the next century if we continue our present trajectory of greenhouse gas emissions.”
A major new study in Science, “A Determination of the Cloud Feedback from Climate Variations over the Past Decade,” (subs. req’d) uses observations to answer what is probably the most important uncertainty in the climate models: What is the feedback from clouds?
Now we can be confident the feedback is likely positive, and exceedingly unlikely to be negative enough to counter the many other positive, amplifying feedbacks. In short, as Dessler says, “This work suggests that climate models are doing a pretty decent job simulating how clouds respond to changing climates.” Recent studies have come to a similar conclusion — see Journal of Climate: New cloud feedback results “provide support for the high end of current estimates of global climate sensitivity.”
Because this is such an important issue — and because this study should be the final nail in the coffin of the central denier myth that the climate has a low sensitivity to CO2 — this post includes two videos explaining the study, an exclusive comment on the study by one of the leading experts on the cloud feedback (NCAR’s Kevin Trenberth), and Dessler’s debunking of the laughable conspiracy-laden response by a discredited disinformer (Roy Spencer).
Perhaps the most important point about the study is that it is the first of its kind based on actual observation, as the Texas A&M news release quoted above explains:
Dessler used measurements from the Clouds and the Earth’s Radiant Energy System (CERES) instrument onboard NASA’s Terra satellite to calculate the amount of energy trapped by clouds as the climate varied over the last decade. He also used meteorological analyses provided by NASA’s Modern Era Retrospective-Analysis for Research and Applications (MERRA) and by the European Center for Medium-Range Weather Forecasts.
Here is Dessler explaining the study in a short video:
As Dessler notes of the cloud feedback issue, “There’s never been a measurement of that using observations.”
Dessler put together a more technical videos — with charts — explaining the study:
Dr. Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, is one of the leading experts on cloud modeling. He had been critical of some recent studies on the cloud feedback effect, so I asked for his thoughts on this study. He replied:
The work is sound and is a very useful contribution. It is a foil to some of the misleading work that Richard Lindzen has published (and which we have shown is wrong). Kudos to Andy Dessler for trying to do this and doing it as well as it can be done.
He also offered some advice for improving the study, which I passed on to Dessler, and made the point about “the preliminary nature of the result owing to the short data record and the weather noise.”
Lindzen has been pushing the “clouds are a negative feedback” theory with bad analysis for a long time — see Lindzen debunked again: New scientific study finds his paper downplaying dangers of human-caused warming is “seriously in error”; Trenberth: The flaws in Lindzen-Choi paper “have all the appearance of the authors having contrived to get the answer they got.”
Lindzen isn’t the only discredited disinformer desperately trying to push back against the tide of scientific analysis and observations. Science magazine’s story, “El Niño Lends More Confidence to Strong Global Warming,” notes:
[Dessler's] result is “convincing evidence” that—at least on the scale of decades—clouds do not counter warming, says climate researcher Brian Soden of the University of Miami in Florida….
“This is a very important check of the models,” says climate researcher Qiang Fu of the University of Washington, Seattle. “It shows no evidence of a large negative cloud feedback.” But climate researcher Roy Spencer of the University of Alabama, Huntsville, disagrees. He published one of the two papers finding evidence of a strongly negative cloud feedback. He finds in his own analyses signs that Dessler is seeing not only cloud changes caused by temperature changes but also temperature changes caused by natural cloud fluctuations. Such effects garble the true negative feedback beyond recognition, he says.
Spencer’s “interpretation is wrong,” says Soden, but even if Spencer were right that there’s a cause-and-effect problem, Dessler’s method of comparing observations and models “eliminates some possibilities, such as the models being egregiously wrong. It’s about as good as we can do with current data sets.”
Few of the climate science disinformers have been as wrong — dead wrong — as Spencer for as long. He famously made a bunch of analytical blunders and spent years pushing the now long-overturned notion that the satellite data didn’t show significant warming (see “Should you believe anything John Christy and Roy Spencer say?“). As RealClimate explained:
We now know, of course, that the satellite data set confirms that the climate is warming , and indeed at very nearly the same rate as indicated by the surface temperature records. Now, there’s nothing wrong with making mistakes when pursuing an innovative observational method, but Spencer and Christy sat by for most of a decade allowing — indeed encouraging — the use of their data set as an icon for global warming skeptics. They committed serial errors in the data analysis, but insisted they were right and models and thermometers were wrong. They did little or nothing to root out possible sources of errors, and left it to others to clean up the mess, as has now been done.
So after that history, we’re supposed to savor all Roy’s new cookery?
So I think the working assumption should be that when Spencer pushes some convoluted new analysis to justify his views, it’s more cookery — an assumption that has so far stood the test of time as Spencer’s claims have grown more absurd over time [see The Great Global Warming Blunder: Roy Spencer asserts (and Morano parrots), “I predict that the proposed cure for global warming – reducing greenhouse gas emissions – will someday seem as outdated as using leeches to cure human illnesses.” Uhh, guys, doctors still use medicinal leeches!]
Yet more outrageous charges can be found in Spencer’s latest blog, “The Dessler Cloud Feedback Paper in Science: A Step Backward for Climate Research.” Dessler easily swats aside the substance of what Spencer says in a new post on RC:
Dr. Spencer is arguing that clouds are causing ENSO [El Niño southern oscillation] cycles, so the direction of causality in my analysis is incorrect and my conclusions are in error.After reading this, I initiated a cordial and useful exchange of e-mails with Dr. Spencer (you can read the full e-mail exchange here). We ultimately agreed that the fundamental disagreement between us is over what causes ENSO. Short paraphrase:
Spencer: ENSO is caused by clouds. You cannot infer the response of clouds to surface temperature in such a situation.
Dessler: ENSO is not caused by clouds, but is driven by internal dynamics of the ocean-atmosphere system. Clouds may amplify the warming, and that’s the cloud feedback I’m trying to measure.
My position is the mainstream one, backed up by decades of research. This mainstream theory is quite successful at simulating almost all of the aspects of ENSO.
Dr. Spencer, on the other hand, is as far out of the mainstream when it comes to ENSO as he is when it comes to climate change. He is advancing here a completely new and untested theory of ENSO — based on just one figure in one of his papers (and, as I told him in one of our e-mails, there are other interpretations of those data that do not agree with his interpretation).
Thus, the burden of proof is Dr. Spencer to show that his theory of causality during ENSO is correct. He is, at present, far from meeting that burden. And until Dr. Spencer satisfies this burden, I don’t think anyone can take his criticisms seriously.
It’s also worth noting that the picture I’m painting of our disagreement (and backed up by the e-mail exchange linked above) is quite different from the picture provided by Dr. Spencer on his blog. His blog is full of conspiracies and purposeful suppression of the truth. In particular, he accuses me of ignoring his work. But as you can see, I have not ignored it — I have dismissed it because I think it has no merit. That’s quite different.
Snap!
Spencer goes the full X-Files — hey, folks said I was using “jump the shark” too much — on his blog:
Dessler’s paper is being announced on probably THE best day for it to support the IPCC’s COP-16 meeting here in Cancun, and whatever agreement is announced tomorrow in the way of international climate policy.
I suspect – but have no proof of it – that Dessler was under pressure to get this paper published to blunt the negative impact our work has had on the IPCC’s efforts.
This is tinfoil-hat stuff.
No single scientific paper — not even a major one like this — could possibly influence the meeting in Cancun, which is the UNFCCC (United Nations Framework Convention on Climate Change), not IPCC! There are hundreds and hundreds of scientific papers that provide more than enough motivation to act — including more than three dozen in the last year alone, see “A stunning year in climate science reveals that human civilization is on the precipice” and “Royal Society special issue details ‘hellish vision’ of 7°F (4°C) world — which we may face in the 2060s!”
Dessler writes:
I would also like to respond to his accusation that the timing of the paper is somehow connected to the IPCC’s meeting in Cancun. I can assure everyone that no one pressured me in any aspect of the publication of this paper. As Dr. Spencer knows well, authors have no control over when a paper ultimately gets published.
In fact, the key phrase Spencer uses is one that pretty much sums up his entire body of work, especially his claims that the climate sensitivity is low: “I … have no proof of it.”
climateprogress.org |
