Attribution of disaster losses.

IN HIS VIEWPOINT “INSURANCE IN A CLIMATE OF change” (12 Aug., p. 1040), E. Mills suggests that changes in climate have been responsible for some part of the trend in recent decades of increasing damage related to extreme weather. This claim is not supported by the peer-reviewed literature, including the most recent report of the Intergovernmental Panel on Climate Change (IPCC) (1). Over recent decades, the IPCC found no long-term global trends in extratropical cyclones (i.e., hurricanes or winter storms), in “droughts or wet spells,” or in “tornados, hail, and other severe weather” (2). Logically, in the absence of trends in these weather events, they cannot be responsible for any part of the growing economic toll. The IPCC did find “a widespread increase in heavy and extreme precipitation events in regions where total precipitation has increased, e.g., the midand high latitudes of the Northern Hemisphere” (3). But at the same time, the IPCC warned that “an increase (or decrease) in heavy precipitation events may not necessarily translate into annual peak (or low) river levels” (3). Indeed, although the IPCC found some changes in streamflow, it did not identify changes in streamflow extremes (i.e., floods) and concluded on a regional basis, “Even if a trend is identified, it may be difficult to attribute it to global warming because of other changes that are continuing in a catchment” (4). These findings are consistent with research seeking to document a climate signal in a long-term record of flood damage that has concluded that an increase in precipitation contributes to increasing flood damage, but the precise amount of this increase is small and difficult to identify in the context of the much larger effects of policy and the ever-growing societal vulnerability to flood damage (5, 6). A recent study by the International Ad Hoc Detection and Attribution Group concluded that it was unable to detect an anthropogenic signal in global precipitation (7). In 2005 several studies reported an increase in the intensity of tropical cyclones (8, 9); however, long-term records of economic damages show no upward trend, once the data are normalized to remove the effects of societal changes (10, 11). Presently, there is simply no scientific basis for claims that the escalating cost of disasters is the result of anything other than increasing societal vulnerability (12).