A new United Nations report projects man-made global warming will boost the damage caused by heat waves, coastal floods, and droughts as they get worse by the end of the century.
In a press release about the report, Special Report for Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX), Intergovernmental Panel of Climate Change Co-Chair Qin Dahe expressed high confidence that temperatures have increased due to man-made global warming. The study further expressed medium confidence that droughts had increased in some areas as a result of man-made climate change. However, the researchers could not draw firm conclusions about the effects of climate change on any trends in hurricanes, typhoons, hailstorms, or tornadoes. (The full report detailing the scientific work behind the study will not be released until February.)
It is generally agreed that the average temperatures over land have increased by about 1° Celsius[PDF] since the 1950s. Looking toward the end of the 21st century, the report relies on computer model projections which suggest that 1-in-20 year hottest day events are to become a 1-in-2 year events. The report also projects that inundations that once happened every 20 years are likely to occur every five years.
Sounds bad, but that's a hundred years from now. With regard to the next few decades, the researchers more sanguinely report, "Projected changes in climate extremes under different emissions scenarios generally do not strongly diverge in the coming two to three decades, but these signals are relatively small compared to natural climate variability over this time frame. Even the sign of projected changes in some climate extremes over this time frame is uncertain." That means that weather extremes for the next several decades will likely be within the limits of natural variation, making it almost impossible to discern any effect of man-made climate change on them. In other words, whatever weather disasters do occur will not be on a scale or frequency beyond those that humanity has experienced in recent decades.
More crucially, the U.N. report acknowledges, "In many regions, the main drivers for future increases in economic losses due to some climate extremes will be socioeconomic in nature." The upshot is that any increase in weather disaster damage is largely due to an increase in what can potentially be destroyed and the number of people exposed to it.
Can researchers discern any effect that the recent increase in global average temperature has had on people and their property? Not really.
For example, a recent Reason Foundation report [PDF], Wealth and Safety: The Amazing Decline in Deaths from Extreme Weather in an Era of Global Warming, 1900–2010, notes, "Aggregate mortality attributed to all extreme weather events globally has declined by more than 90 percent since the 1920s, in spite of a four-fold rise in population and much more complete reporting of such events." The death rate from droughts is 99.9 percent lower than it was in the 1920s; the death rate from floods is 98 percent lower; and the death rate from big storms like hurricanes has declined more than 55 percent since the 1970s.
Keep in mind that the death rate due to extreme weather between 2001 and 2010 averaged about 38,000 per year compared to about 59 million annual deaths for all causes. The Reason Foundation report concludes, "While extreme weather-related events, because of their episodic nature, garner plenty of attention worldwide, their contribution to the global mortality burden—0.07 percent of global deaths—is relatively minor."
What about economic losses? Proponents of catastrophic man-made climate change have been seeking evidence that it is boosting risks among the weather damage and loss data. A recent review article[PDF], "Have Disaster Losses Increased Due to Anthropogenic Climate Change?" by Laurens Bouwer, published in the Bulletin of the American Meteorological Society (BAMS), surveyed 22 studies looking at trends in natural hazard losses. Bouwer, a researcher in the Institute for Environmental Studies at Vrije University in the Netherlands, included studies that all looked at economic losses, covered at least 30 years of data, and were peer reviewed.
Generally loss data are normalized to take into account inflation, and changes in exposure and vulnerability associated with increases in wealth and population. The BAMS review found, "The studies show no trends in the losses, corrected for change (increases) in population and capital at risk, that could be attributed to anthropogenic climate change. Therefore, it can be concluded that anthropogenic climate change so far has not had a significant impact on losses from natural disasters."
Another recent study, "Normalizing economic loss from natural disasters: global analysis," by Eric Neumayer and Fabian Barthel, two researchers associated with the Grantham Research Institute on Climate Change and the Environment at the London School of Economics and Political Science, also probed trends in weather disaster loss data in search of a global warming signal. Besides using conventional techniques that take into account increases in population and wealth to normalize losses, they also develop an alternative technique that looks at relative losses over time. Briefly, their new measure looks at how much actual loss occurred relative to the amount that was at risk. For example, what percentage of wealth in Miami was destroyed by hurricanes in 1920 versus 2010? If the actual-to-potential-loss ratio is increasing over time, this suggests that the weather is having a growing impact.
Analyzing weather disasters between 1980 and 2009, Neumayer and Barthel find, "Both methods lead to the same result for all disasters: no significant trend over time according to the conventional method, a marginally significant downward trend according to the alternative method." Applying both normalization methods, they find no significant trends in weather related losses for both developed and developing countries. Looking regionally at North America, Western Europe, Latin America and the Caribbean, and South and East Asia also uncovers no statistically significant trend in losses caused by weather disasters. In addition, two 2009 studies found no upward trend in normalized losses dues to windstorm or floods in Western Europe since 1970. One concluded, "Results show no detectable sign of human-induced climate change in normalized flood losses in Europe."
Neumayer and Barthel, using their alternative normalization method, do identify a "strongly negative trend" in normalized weather disaster damages in developed countries. They speculate, "This could possibly indicate a stronger capability of richer nations to fund defensive mitigating measures, which decrease vulnerability to natural disasters over time." Richer societies are likely reducing their weather losses by establishing better early warning systems, enacting stronger building codes, and constructing firmer levees. People may be protecting themselves ever better against the consequences of storms and floods, even though the weather is getting worse.
Although no upward trend in weather damages can be found in developing countries, the U.N.'s SREX report does note that fatality rates and economic losses as a proportion of GDP from weather disasters are higher in poor countries. In fact, between 1970 and 2008, 95 percent of deaths from natural disasters occurred in developing countries. Bad weather produces death and destruction largely when it encounters poverty.
Let's conclude with two observations: First, recent research indicates that man-made climate change has not been nor is it likely to be a big contributor to losses stemming from weather disasters in the next few decades. Second, boosting the wealth of poor people through economic growth is their best protection against meteorological disasters in the long run, whether fueled by future man-made climate change or not.
Ronald Bailey is Reason's science correspondent. His book Liberation Biology: The Scientific and Moral Case for the Biotech Revolution is available from Prometheus Books.