An Open Challenge to Climate Modelers for 2009

December 31st, 2008 by Roy W. Spencer, Ph. D.

Back in 1997, Bob Cess (climate researcher, cloud expert) said in an interview with Science magazine’s Richard Kerr,

“…the [climate models] may be agreeing now simply because they’re all tending to do the same thing wrong. It’s not clear to me that we have clouds right by any stretch of the imagination.”

In the last year or so I have become convinced that this is indeed what has happened…..the models are all doing the “same thing wrong”. While I have addressed this before, I am going to continue to harp on this issue until one or more climate modelers finally has a light bulb go on in their head and says, “Ahhh…I see what you’re talking about now…”. The issue is critical, and could completely change our perception of the role of clouds in climate change.

First, though, a little background for the uninitiated. Modern climate change theory is all about radiative forcing (aka, radiative energy imbalance) of the climate system: Something causes either a change in the rate at which solar energy is absorbed by the Earth (for instance, a major volcanic eruption), or the rate at which the Earth emits infrared energy back to outer space (for instance, increasing atmospheric carbon dioxide concentrations). The resulting global average radiative energy imbalance then causes a temperature change. This part of the theory is seldom disputed.

But that temperature change, in turn, causes other elements of the climate system – clouds, water vapor, etc. – to also be altered, which then feeds back on the original temperature change by amplifying it (positive feedback) or reducing it (negative feedback). Those feedbacks are what will determine whether manmade global warming will be either lost in the noise of natural climate variability, or — as NASA’s James Hansen believes — catastrophic. Feedbacks in the climate system are much less certain than the radiative forcing from extra carbon dioxide.

All twenty climate models tracked by the IPCC now have positive cloud feedbacks, which is partly why they project so much global warming in the future. Obviously, we desperately need to know what cloud feedbacks are occurring in the real climate system. And since one needs global observations to do that, it can only be done (if at all) during the modern satellite era.

But some researchers now think the search for the feedback “Holy Grail” is a lost cause. This is partly because researchers get different answers depending on which years of satellite observations are analyzed.

But I think I have discovered why. The issue is not a new one to the climate research community, and it is really quite simple: In order to estimate radiative feedbacks, one must first remove any sources of radiative forcing present in the data.

This ‘radiative forcing removal’ technique has been performed before by Forster & Gregory (2006 J. of Climate) to estimate feedbacks during the global cooling which occurred after the 1991 eruption of Mt. Pinatubo. They removed an estimate of the radiative forcing caused by the volcanic aerosols in the stratosphere in order to estimate radiative feedbacks.

Similarly, Forster & Taylor (also 2006 J. Climate) removed anthropogenic radiative forcings from the output of 20 IPCC climate models in order to diagnose the radiative feedbacks operating in those models.

Well, what researchers haven’t accounted for is that there are natural cloud variations in the real climate system, and these also cause radiative forcing. So, in order to estimate feedbacks in the real climate system from satellite data, one would need to first remove those radiative forcings. Unfortunately, this is not easy because those forcings are somewhat chaotic…but, as I
show, they have distinctly different signatures in the data.

Because this ‘contamination’ of the feedback signature by internally-generated radiative forcing by clouds has never been taken into account before, diagnosed feedbacks have been both quite variable (depending upon the time period analyzed), AND they have been significantly biased in the direction of positive feedback.

The result has been the illusion of a sensitive climate system with positive cloud feedback….when in fact the satellite evidence, after accounting for this effect, reveals cloud feedbacks to be negative.

The article I posted here contains the details on all of this, including what I believe to be the most stringent test of climate model feedbacks ever performed. In it I present proof that this natural radiative forcing by clouds is strong, and ever-present…even in the climate models themselves!

I also provide the first evidence that the short-term feedbacks in the IPCC models are substantially the same as their long-term feedbacks in response to anthropogenic radiative forcing — a key finding if we are to ever apply our short-term satellite observations to the long-term global warming problem.

I challenge modelers to address this important issue, because the current, crude level of model testing has NOT been sufficient to validate feedbacks in climate models.

And yes, some of our early work on this issue has been published in the peer-reviewed literature (Spencer et al., 2007 GRL; Spencer & Braswell, November 1, 2008 J. of Climate). Unfortunately, our work is either being ignored or marginalized.

If anyone has a legitimate objection to my arguments in that article, or think something I’ve presented is not clear, e-mail me (see bottom of this page) and I will post your question and my reply here if I think it would be of general interest. I will not reply to comments or questions which are submitted anonymously.

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