The controversy centres on why the cost of repairs after hurricanes, floods and other natural disasters, has risen from $75.5bn (£46.7bn) in the 1960s to $659.9bn in the 1990s.
Roger Pielke Junior, a professor of environmental studies at the University of Colorado, has attacked the IPCC for including in one of its reports a reference to an abstract in 2006 that indicated economic losses from disasters, even after “normalisation” to take account of inflation and growth in the number of buildings in high-risk areas, increased between 1970 and 2005. The authors of that study, led by Robert Muir-Wood (who works for my former employer, Risk Management Solutions), concluded that “we find evidence of an annual upward trend for normalised losses of 2% per year that corresponds with a period of rising global temperatures”.
The authors offered many caveats about their results, not the least of which was the fact that the rising trend was strongly dependent on economic losses caused by hurricanes in the United States, particularly the nine that hit in 2004 and 2005.
The six-page abstract, taken from a workshop presentation, was cited both in the review of the economics of climate change by Nicholas Stern in 2006 and in Chapter 1 of the volume by working group II in the IPCC Fourth Assessment Report in 2007, which stated: “Global losses reveal rapidly rising costs due to extreme weather-related events since the 1970s”. It pointed out “one study” found that an underlying rising trend in losses still remains, even after adjustments for inflation and increases in the numbers of exposed buildings.
Pielke has several times on his blog since 2006 attacked both the Stern Review and the IPCC report for referring to the work by Muir-Wood. He argues that the abstract from the workshop, which Pielke organised with the company Munich Re (which also funds research at London School of Economics and Political Science on the implications of climate change for the insurance industry), was not peer-reviewed.
Therefore, Pielke insists, the reports should have relied on other papers, such as those that he has written about hurricane losses, which conclude that the upward trend can be explained away completely by economic factors and that there is no evidence for the impact of climate change.
The trouble with Pielke’s argument is that the work of Muir-Wood and his colleagues was eventually published as a peer-reviewed paper in 2008 (and included as chapter 12 of the book Climate Extremes of Society) and included the same conclusion. It remains the only paper to assess global economic losses from all types of extreme weather events, not just a single source of hazard in one region.
Pielke is right that an increase in the number of valuable properties in high-risk areas is overwhelmingly the primary cause of increased financial losses from extreme weather events over the past few decades. That in itself is a worrying conclusion given that climate change is expected to lead to changes in the occurrence and severity of such events. Indeed, only last week a paper in the journal Science by researchers at the United States National Oceanic and Atmospheric Administration projected nearly a doubling in the frequency of the most severe hurricanes in the Atlantic by the end of this century.
But it is difficult to tell to what extent, if any, climate change has also already affected past disaster losses around the world. Extreme weather events are rare, so identifying small trends is difficult when losses vary so much from year to year, creating a lot of “noise” in the dataset, and many competing factors contribute to the overall pattern.
The absence of a “statistically significant” trend may indicate that no trend exists, or instead that a trend exists but cannot be definitively detected until a longer period of losses is available.
What is clear is that it would be wrong to think of this as another mistake by climate researchers. In fact it looks more like a blatant attempt to dig up an old academic row in order to create the impression of an IPCC under siege.
• Bob Ward is policy and communications director at the Grantham Research Institute on Climate Change and the Environment at London School of Economics and Political Science.