From Roger Pielke Jr., in comments Thursday before the U.S. Senate Committee on Environment and Public Works. Mr. Pielke is professor of environmental studies at the University of Colorado.
It is misleading, and just plain incorrect, to claim that disasters associated with hurricanes, tornadoes, floods or droughts have increased on climate timescales either in the United States or globally.
It is further incorrect to associate the increasing costs of disasters with the emission of greenhouse gases.
Globally, weather-related losses ($) have not increased since 1990 as a proportion of GDP (they have actually decreased by about 25%) and insured catastrophe losses have not increased as a proportion of GDP since 1960.
Hurricanes have not increased in the U.S. in frequency, intensity or normalized damage since at least 1900. The same holds for tropical cyclones globally since at least 1970 (when data allows for a global perspective).
Floods have not increased in the U.S. in frequency or intensity since at least 1950. Flood losses as a percentage of U.S. GDP have dropped by about 75% since 1940.
Tornadoes have not increased in frequency, intensity or normalized damage since 1950, and there is some evidence to suggest that they have actually declined.
Drought has for the most part, become shorter, less frequent, and cover a smaller portion of the U. S. over the last century. Globally, there has been little change in drought over the past 60 years.
The absolute costs of disasters will increase significantly in coming years due to greater wealth and populations in locations exposed to extremes. Consequent, disasters will increase significantly in coming years due to greater wealth and populations in locations exposed to extremes. Consequent, disasters will continue to be an important focus of policy, irrespective of the exact future course of climate change.
Because the climate issue is so deeply politicized, it is necessary to include several statements beyond those reported above.
Humans influence the climate system in profound ways, including through the emission of carbon dioxide via the combustion of fossil fuels.
Researchers have detected and (in some cases) attributed a human influence in other measures of climate extremes beyond those discussed in this testimony, including surface temperatures and precipitation.
The inability to detect and attribute changes in hurricanes, floods, tornadoes and drought does not mean that human-caused climate change is not real or of concern.
It does mean however that some activists, politicians, journalists, corporate and government agency representatives and even scientists who should know better have made claims that are unsupportable based on evidence and research.
Such false claims could undermine the credibility of arguments for action on climate change, and to the extent that such false claims confuse those who make decisions related to extreme events, they could lead to poor decision making.
A considerable body of research projects that various extremes may become more frequent and/or intense in the future as a direct consequence of the human emission of carbon dioxide. Our research, and that of others, suggests that assuming that these projections are accurate, it will be many decades, perhaps longer, before the signal of human-caused climate change can be detected in the statistics of hurricanes (and to the extent that statistical properties are similar, in floods, tornadoes, drought).