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The IPCC sea level numbers

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Translations: (Português)

The sea level rise numbers published in the new IPCC report (the Fourth Assessment Report, AR4) have already caused considerable confusion. Many media articles and weblogs suggested there is good news on the sea level issue, with future sea level rise expected to be a lot less compared to the previous IPCC report (the Third Assessment Report, TAR). Some articles reported that IPCC had reduced its sea level projection from 88 cm to 59 cm (35 inches to 23 inches) , some even said it was reduced from 88 cm to 43 cm (17 inches), and there were several other versions as well (see “Broad Irony”). These statements are not correct and the new range up to 59 cm is not the full story. Here I will try to clarify what IPCC actually said and how these numbers were derived. (But if you want to skip the details, you can go straight to the critique or the bottom line).
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Does a Global Temperature Exist?

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Translations: (Português)

Does a global temperature exist? This is the question asked in a recently published article in Journal of Non-Equilibrium Thermodynamics by Christopher Essex, Ross McKitrick, and Bjarne Andresen. The paper argues that the global mean temperature is not physical, and that there may be many other ways of computing a mean which will give different trends.

The common arithmetic mean is just an estimate that provides a measure of the centre value of a batch of measurements (centre of a cloud of data points, and can be written more formally as the integral of x f(x) dx. The whole paper is irrelevant in the context of a climate change because it missed a very central point. CO2 affects all surface temperatures on Earth, and in order to improve the signal-to-noise ratio, an ordinary arithmetic mean will enhance the common signal in all the measurements and suppress the internal variations which are spatially incoherent (e.g. not caused by CO2 or other external forcings). Thus the choice may not need a physical justification, but is part of a scientific test which enables us to get a clearer ‘yes’ or ‘no’. One could choose to look at the global mean sea level instead, which does have a physical meaning because it represents an estimate for the volume of the water in the oceans, but the choice is not crucial as long as the indicator used really responds to the conditions under investigation. And the global mean temperature is indeed a function of the temperature over the whole planetary surface.

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Has Pacific Northwest snowpack declined? Yes.

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There has been a bit of a flap here at the University of Washington over the state of the snowpack in United States Pacific Northwest region. The Seattle city mayor, Greg Nickels (a well known advocate for city-based CO2 reduction initiatives) wrote in an Op-Ed piece in the Seattle Times that

The average snowpack in the Cascades has declined 50 percent since 1950 and will be cut in half again in 30 years if we don’t start addressing the problems of climate change now. That snow not only provides our drinking water, it powers the hydroelectric dams that keep our lights on.
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Adventures on the East Side

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Translations: (Türkçe)

So that was …. interesting.

First off, I’d like to thank the commenters for all of the suggestions and ideas to the previous post. They were certainly useful. In particularly, the connection with the difficulties faced by evolutionists in debates vs. creationists proved to be very a propos. Our side played it it pretty straight – the basic IPCC line (Richard Somerville), commentary on the how ‘scientized’ political debates abuse science (me, though without using the word ‘scientized’!) and the projections and potential solutions (Brenda Ekwurzel). Crichton went with the crowd-pleasing condemnation of private jet-flying liberals – very popular, even among the private jet-flying Eastsiders present) and the apparent hypocrisy of people who think that global warming is a problem using any energy at all. Lindzen used his standard presentation – CO2 will be trivial effect, no one knows anything about aerosols, sensitivity from the 20th Century is tiny, and by the way global warming stopped in 1998. Stott is a bit of a force of nature and essentially accused anyone who thinks global warming is a problem of explicitly rooting for misery and poverty in the third world. He also brought up the whole cosmic ray issue as the next big thing in climate science.
Update: The transcript is now available – though be aware that it has not yet been verified for accuracy. Audio + Podcast.
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Broad Irony

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Michael Mann and Gavin Schmidt

[update 3/20/07: The New York Times has run a short letter from us w/ a link to RealClimate for more info (scroll down to 5th letter; the 2nd letter from James McCarthy of Harvard is quite good too, as are some of the others).]

The first rule when criticizing popular science presentations for inaccuracies should be to double check any ‘facts’ you use. It is rather ironic then that William Broad’s latest piece on Al Gore plays just as loose with them as he accuses Gore of doing.

We criticized William Broad previously (Broadly Misleading) for a piece that misrepresented the scientific understanding of the factors that drive climate change over millions of years, systematically understating the scientifically-established role of greenhouse gases, and over-stating the role of natural factors including those as speculative as cosmic rays (see our recent discussion here). In this piece, Broad attempts to discredit Gore’s “An Inconvenient Truth” by exaggerating the legitimate, but minor, criticisms of his treatment of the science by experts on climate science, and presenting specious or unsubstantiated criticisms by a small number of the usual, well-known contrarians who wouldn’t agree even if Gore read aloud from the latest IPCC report.
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Global Warming debate

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Translations: (Türkçe)

Along with Richard Somerville (UC San Diego) and Brenda Ekwurzel (Union of Concerned Scientists), I’ll be appearing at a debate on Wednesday (March 14th) about whether Global Warming is a crisis (or not). That might have gone without notice (like most of my public talks), except that our opponents are Michael Crichton, Richard Lindzen and Philip Stott. The preliminary position statements (from me and from Philip Stott) are available on the ABCnews site. It’s sold out, but the proceedings will be broadcast on NPR (for instance, WNYC 820 AM on Friday, March 23, 2007 at 2PM) and there will be a podcast (though I don’t know if it will stream live). There’s an online poll as well for what that’s worth.

I’m quite looking forward to this, but I have to admit to conflicting thoughts. Does participating help perpetuate the idea that global warming per se is still up for debate? Is this kind of rhetorical jousting useful for clarifying issues of science that most people there will only superficially grasp? Can this be entertaining and educational? Or does it just validate the least serious opposition? Is it simply a waste of time that would be better spent blogging? ;)

I’d be interested in any thoughts people might have.

Swindled: Carl Wunsch responds

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Translations: (Türkçe)

The following letter from Carl Wunsch is intended to clarify his views on global warming in general, and the The Great Global Warming Swindle which misrepresented them.

Partial Response to the London Channel 4 Film “The Global Warming Swindle”

Carl Wunsch 11 March 2007

I believe that climate change is real, a major threat, and almost surely has a major human-induced component. But I have tried to stay out of the `climate wars’ because all nuance tends to be lost, and the distinction between what we know firmly, as scientists, and what we suspect is happening, is so difficult to maintain in the presence of rhetorical excess. In the long run, our credibility as scientists rests on being very careful of, and protective of, our authority and expertise.
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Swindled!

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Translations: (Türkçe)

By William and Gavin

On Thursday March 8th, the UK TV Channel 4 aired a programme titled “The Great Global Warming Swindle”. We were hoping for important revelations and final proof that we have all been hornswoggled by the climate Illuminati, but it just repeated the usual specious claims we hear all the time. We feel swindled. Indeed we are not the only ones: Carl Wunsch (who was a surprise addition to the cast) was apparently misled into thinking this was going to be a balanced look at the issues (the producers have a history of doing this), but who found himself put into a very different context indeed [Update: a full letter from Wunsch appears as comment 109 on this post]

So what did they have to say for themselves?
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‘Cosmoclimatology’ – tired old arguments in new clothes

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Translations: (Português)

Image from cosmosIn a recent issue of the journal Astronomy and Geophysics (A&G), Henrik Svensmark coined a new term: ‘cosmoclimatology’ . I think ‘cosmoclimatology’ is a good and refreshing name for anything combining our cosmos with our climate. However, all other aspects of the article I found very disappointing. We have already covered most of these topics before, but the A&G articles provides us with some new aspects to discuss. Furthermore, Svensmark is the Director for Center for Sun-Climate Research, Danish National Space Center, and therefore influential. He is also the co-author of a recent book with Nigel Calder that received some attention. Furthermore, a laboratory experiment of his also managed to make some headlines. It seems that solar forcing is one of the sceptics’ last trenches in the debate about climate change. In my view the A&G paper therefore merits a comment as long as the same old and worn arguments resurface without discussing misgivings from the critics.

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