Thursday, January 10, 2008

Global Climate Modeling: Fact or Fiction, And How Much Truth?

Global Climate Modeling: What Temperatures To Use, What Variables Are There?
John Tierney, a columnist for the New York Times is beginning to ask some probing questions about global warming and the science behind the global climate models used for predictions. He is expressing a good deal of doubt. Of course skeptics (like me) have more than just a little doubt, as even a brief review of material on my blog will show. I think it is a positive sign that the large, liberal, mainstream media like the New York Times is beginning to question the Al Gore and United Nations views on climate. It is about time.


January 10, 2008, 8:58 am

A Spot Check of Global Warming

How do predictions by the Intergovernmental Panel on Climate Change jibe with reality? The solid brown line shows the warming projected by the IPCC, with a range of uncertainty bounded by the dotted brown lines. The other lines show the actual temperatures recorded during the past seven years by different methods on the ground and by satellite. (The lines show the amount of warming, in degrees Celsius, relative to the average temperature during the last two decades of the 20th century.) (Source: Roger A. Pielke, Jr.)
Last week I asked if there were any good weather omens to look for. I raised a question originally posed by Roger A. Pielke Jr., a professor of environmental studies at the University of Colorado: Are there any indicators in the next 1, 5 or 10 years that would be inconsistent with the consensus view on climate change?Lab readers contributed some ideas (and much invective), but I think the most useful one came from a climate scientist who wrote directly to Dr. Pielke and suggested comparing what has happened since 2000 with the predictions made by the Intergovernmental Panel on Climate Change.
Dr. Pielke took up the suggestion and looked at the increase in global average temperature projected by the IPCC from 2000 to 2007. (The IPCC projected various scenarios, depending on the rate of greenhouse emissions; Dr. Pielke chose the scenario that most closely matches the actual emissions since 2000.) The hard part was figuring out what has actually happened the past seven years, because it all depends on who’s doing the measuring, and whether it’s being done on the surface or by satellite.
As you can see from the blue line in the graph above, the recent surface measurements by NASA (the blue line) are warmer than those by the United Kingdom Met Office (the green line), and there are different satellite measurements from Remote Sensing Systems and the University of Alabama in Huntsville.Dr. Pielke calls it “a feast for cherrypickers.”
In the Prometheus blog, where you can read the details of his computations, he writes: “One can arrive at whatever conclusion one wants with respect to the IPCC predictions. Want the temperature record to be consistent with IPCC? OK, then you like NASA. How about inconsistent? Well, then you are a fan of RSS. On the fence? Well, UAH and UKMET serve that purpose pretty well.”No matter which line you prefer on the graph, you can’t draw any firm conclusions about the IPCC’s projections — a few years does not a trend make, and the global temperature is just one of the indicators to look at. But the different lines on the graph are certainly evidence of how complicated the climate debate is.
If scientists can’t even agree on what has happened in the past, imagine how much more difficult it is to figure out the future. I’m not suggesting that the global warming isn’t real, or that the uncertainties justify inaction — we take out insurance all the time against risks that are uncertain. I’d like to see a carbon tax. But I’d also like to see fewer dogmatists claiming that the scientific debate is over.
Dr. Pielke suggests that more scientists do reality checks on other predictions by the IPCC, and that the IPCC make it easier for its predictions to be tested by specifying in detail what the variables are, who is measuring them, and what to look for in the future. “If weather forecasters, stock brokers, and gamblers can do it, then you can too,” he urges the IPCC in his blog post.
Dr. Pielke told me that scientists have been focusing on the predictions for the summer ice melt in the Arctic — which called for less dramatic change than what has actually occurred — but not paying enough attention to other indicators.“Rather than select among predictions, why not verify them all?” he said. “Seven years is not a lot to allow much to be said, but certainly 10 and 15 years will be. Once predictions are made, they should not be forgotten, but evaluated against experience. This is not skepticism at work, just the good old scientific method.”
If you’ve got any thoughts on how to interpret the results on Dr. Pielke’s graph — or how to look for other indicators — let me know. I’d be glad to hear suggestions from scientists at the popular Real Climate blog on a short list of variables (beyond temperature and sea ice) that might be used to compare with specific IPCC predictions and point interested readers to where data on them can be found.

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