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The IPCC sea level numbers

Filed under: — stefan @ 27 March 2007 - (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?

Filed under: — rasmus @ 25 March 2007 - (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.

Filed under: — eric @ 20 March 2007

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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A much more eloquent rebuttal of TGGWS

Filed under: — gavin @ 17 March 2007

Promoted from the comments, the download of the BBC Radio 4 ‘Now Show’ (Mar 16) is available here (at least for now). Key bit starts at about 18min in, (the rest of the show is pretty funny too).

Adventures on the East Side

Filed under: — gavin @ 15 March 2007 - (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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