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Testing greenhouse

By Mark S. Lawson - posted Friday, 23 January 2009

The crisis in the world markets has pushed the debate over the enhanced greenhouse effect off front pages everywhere, and may keep it off for some time. By the time it returns, thanks to a surprise turn in events, we may even be in a position to decide whether our climate future will be hotter, and just how much hotter it may be.

For as a journalist who has been harangued by scientists, held discussions with scientists, chatted with scientists, swapped emails and phone calls with scientists in Australia, the US and Europe, gone through more scientific literature and material from both sides than I care to admit, I believe I am in a position to propose a test based on trends in global temperatures. That test may take perhaps three to four years, or maybe just two.

To run through some basic points, as matters stand the proposition that industrial gases are substantially affecting the process of climate change is undoubtedly scientific orthodoxy. But it is an orthodoxy that rests on the results of a slew of computer models, the results of which are collated and periodically interpreted by the Intergovernmental Panel on Climate Change.


A fair sample of this approach to proving climate propositions through computer models is given in "Attribution of polar warming to human influence" (Nature Geoscience Online, October 30, 2008). The nine authors led by Nathan P. Gillett of the Climate Research Unit of the University of East Anglica, a bastion of greenhouse theory, ran IPCC climate models with natural climate drivers and the same models with human-induced forcings and, after some fancy statistical techniques, found that the ones with the artificial factors were a better fit for historical records in the poplar regions. The authors concluded that the results were sufficient proof that industrial gases had affected climate in both the Arctic and Antarctic (that is, as formal proof, rather than looking at changes in summer sea ice coverage and claiming it must be due to global warming). The 2007 IPCC report had stated that it was hard to identify evidence of artificial warming in the region.

Apart from this form of “proof”, everything else usually cited in the media - all the way from the reduction of summer ice in the Arctic through to reports of species extinction in Africa - indicate that climate is changing, but without telling us anything about what is causing the change.

So we are back to the models - an approach that has become almost universal in climate studies, and certainly endorsed by the nine authors of the paper, all from top rank institutions. Further, although computer models have a mixed track record in science, to say the least, there has been no serious challenge to this use of computer models by the rest of the scientific community. So let us wave any doubts laymen, such as myself, might have about relying so heavily on untested models.

Let us also wave aside the points made by David Dale in a recent posting on this site that the computer models fail to show a distinctive pattern of warming in the troposphere - the so called Tropospheric fingerprint test. Climatologists have acknowledged the objection but broadly dismissed it as something to be accommodated later with improved models or measuring techniques, or whatever. They say the same thing for the failure of the models to model anything earlier than 1900 or so, including the extremely warm period in the middle of the Cretaceous, about 50 to 100 million years ago when the Antarctica was warm and forested (see New Scientist cover story, June 21, "When crocodiles roamed the artic"). But the climate modellers do have one “almost-win”, which I propose as the basis for an easily understandable test.

Lawson climate change

That “almost-win” is in a paper published last year, Recent Climate Observations Compared to Predictions (Science, May 4, 2007). The paper, which lists nine authors led by Stefan Rahmstorf, a Professor of Physics of the Oceans at Potsdam University in Germany and including the redoubtable James Hansen, states that warming since 2001 is at the top of the range for forecasts set out in the 2001 IPCC report. The paper is occasionally cited in the Australian debate as evidence that the earth is warming faster than expected.


The claim seems incredible if taken at face value. Temperatures have fallen since 2001 on all sites that track temperatures except the Hansen-controlled Goddard site. However, on my own very rough graph work, set out on the graph attached to this story, it is possible to sustain the claim. I have graphed actual temperatures from the Hadley site, calculated a five-year average and imposed the top IPCC forecast estimated off the 2001 report (hence the waviness of the line). I started the forecast from about the same place as the five-year average in 1990, which is the Kyoto year. A win? A closer look at the graph shows that the bulk of the warming took place before the forecast was made. In fact, average temperatures were already higher than the top range of the forecasts at the time the forecasts were issued. Again, let us wave those niggling doubts away. Professor Rahmstorf has assured me, by email, that the line has been calculated from the physics of climate change, and not adjusted or tuned to suit the actual results. So instead let us nail it to the greenhouse mast, particularly as the next few years are crucial for that forecast.

In the 2001 forecasts the slope of the top line becomes steeper with every year but, as we can see, observed temperatures have been flat-lining and even falling in recent years, so unless observed temperatures turn up soon the top line will soon be far above reality. Already observed temperatures for 2008, at least according to Hadley and my efforts at estimation, are more than 0.2 degrees below the top line. Two or three more years of present trends and they will be so different we may be able to dismiss apocalypse. This is one part of the test I propose.

Why not use the IPCC forecasts released in 2007 which kicked off a lot of the present fuss about climate? They were only released in early 2007 and no one has produced papers claiming the forecasts are a success. In any case, although I have not looked at the 2007 forecasts in detail, I suspect they have been reset.

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This article is adapted from one published in the Summer 2008-2009 issue of The Skeptic, produced by the Australian Skeptics.

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About the Author

Mark Lawson is a senior journalist at the Australian Financial Review. He has written The Zen of Being Grumpy (Connor Court).

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