Wednesday, December 06, 2006

Shades of Bjorn Lomborg?

For those who have not yet seen it Roger Pielke Jr. has criticised the Stern report's treatment of extreme weather events. Basically Pielke accuses the Stern team of "cherry picking" certain phrases from published reports giving a misleading sense of their contents. Here's what he had to say:

The Stern Report has this passage on p. 131:

The costs of extreme weather events are already high and rising, with annual losses of around $60 billion since the 1990s (0.2% of World GDP), and record costs of $200 billion in 2005 (more than 0.5% of World GDP). New analysis based on insurance industry data has shown that weather-related catastrophe losses have increased by 2% each year since the 1970s over and above changes in wealth, inflation and population growth/movement. If this trend continued or intensified with rising global temperatures, losses from extreme weather could reach 0.5 - 1% of world GDP by the middle of the century. If temperatures continued to rise over the second half of the century, costs could reach several percent of GDP each year, particularly because the damages increase disproportionately at higher temperatures.

The source is a paper prepared by Robert Muir-Wood and colleagues as input to our workshop last May on disasters and climate change. Muir-Wood et al. do report the 2% trend since 1970. What Stern Report does not say is that Muir-Wood et al. find no trend 1950-2005 and Muir-Wood et al. acknowledge that their work shows a very strong influence of 2004 and 2005 hurricane seasons in the United States. Muir-Wood et al. are therefore very cautious and responsible about their analysis. Presumably this is one reason why at the workshop Robert Muir-Wood signed on to our consensus statements, which said the following:

Because of issues related to data quality, the stochastic nature of extreme event impacts, length of time series, and various societal factors present in the disaster loss record, it is still not possible to determine the portion of the increase in damages that might be attributed to climate change due to GHG emissions . . . In the near future the quantitative link (attribution) of trends in storm and flood losses to climate changes related to GHG emissions is unlikely to be answered unequivocally.

The Stern Report’s selective fishing out of a convenient statement from one of the background papers prepared for our workshop is a classic example of cherry picking a result from a diversity of perspectives, rather than focusing on the consensus of the entire spectrum of experts that participated in our meeting. The Stern Report even cherry picks from within the Muir-Wood et al. paper.

Why does this matter? The Stern Report uses the cherry-picked information as the basis for one of its important conclusions about the projected costs of climate change(on p. 138),

The costs of climate change for developed countries could reach several percent of GDP as higher temperatures lead to a sharp increase in extreme weather events and large-scale changes.

To support its argument the Stern Report further relies on a significantly flawed report from the Association of British Insurers, which we critiqued here. Its presentation of the future costs of disasters and climate change is highly selective to put it mildly.

I haven’t yet read the whole Stern report, but if its treatment of disaster costs and climate change – an area where I do have some expertise – is indicative of its broader analysis, then Richard Tol’s comment in the open thread would appear to be on target.

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