A scary graph appeared on the New York Times op-ed page on Sunday. It seems to show a profound acceleration in the rate of natural disaster in the United States and the world. In the words of its author, Charles Blow:
According to the Center for Research on the Epidemiology of Disasters, there have been more than four times as many weather-related disasters in the last 30 years than in the previous 75 years. The United States has experienced more of those disasters than any other country.
Who do we have to thank for all this? Probably ourselves.
Last year, the Intergovernmental Panel on Climate Change issued reports concluding that "human influences" (read greenhouse-gas emissions) have "more likely than not" contributed to this increase. The United States is one of the biggest producers of greenhouse-gas emissions.
However, his source—the Centre for Research on the Epidemiology of Disasters —states the obvious problem with Blow's figures, one that Blow neglects to mention to his readers: that reporting has greatly improved over the decades. As one of its reports notes, the annual number of earthquakes appears to have increased over the decades, but no one thinks that earthquakes are caused by climate change. What has changed is the quality of earthquake-monitoring systems, the reliability of government records, and so forth. (While it is true that the incidence of hurricanes has increased over the last few decades, there remains a great deal of scientific controversy about whether this trend will continue.) The pre-1970 data, which are responsible for most of the dramatic rise in the graph, are probably worthless.
There is another data artifact that drives Blow's graph, one that is also well-known in the scientific community . The main reason for the increase in the number and costliness of natural disasters in the United States, and probably in other countries as well, is that people have been moving to the most vulnerable areas—the coasts (especially Florida and California)—and building expensive structures there. CRED defines a natural disaster as an event where 10 or more people are reported killed, 100 people or more are reported affected, a declaration of a state of emergency occurs, or a call for international assistance is made. Obviously, all these criteria are more likely to be met when a hurricane, earthquake, or other natural disaster occurs in a highly populated area than when it occurs in a sparsely populated area.
This is not to deny that some extreme weather events—droughts and flooding, for example—may be connected to climate change. It's just to point out that there is a difference between reporting the facts and scaring people with misleading statistics. Blow is right to worry about climate change and to urge the United States to join international efforts to curb greenhouse-gas emissions. But he misuses the data to make this point—despite CRED's repeated warnings about reporting and data problems—and as a result, he misses the main implication of the data: that the United States and state governments should regulate construction in coastal and other vulnerable areas more strictly. This is much more important in the short run than a climate treaty, as the benefits of a reduction in greenhouse-gas emissions won't be felt for decades. As CRED says in the report cited above, "Disaster data—handle with care!"