What was done
The authors determined the costs of natural disasters in the United States in five-year increments from 1952-56 through 1992-96, finding a several-fold increase over just the last decade.  They then analyzed a number of factors to answer this question: "Could an explanation for the increase in costs of natural disasters be a corresponding increase in the frequency or severity of natural events, or both?"

What was learned
In studying a number of potentially dangerous natural phenomena, the authors could identify no significant trends over the period of their study.  However, they did find that (1) more people are moving into coastal areas that are vulnerable to natural hazards, (2) the effect of this population shift is amplified because the people who are moving into these areas come from the wealthier segment of society, and (3) the wealth of these wealthy people has been rising at a dramatic rate.  It was consequently their conclusion that, although it could be theorized (and indeed often is) that global phenomena such as climate and sea level change might possibly amplify the impact of certain disasters, such as hurricanes, floods and tornadoes, "they do not explain the large increase in U.S. costs over the last decade."  Instead, they were driven by the data to conclude that "we are becoming more vulnerable to natural disasters because of the trends of our society rather than those of nature."

What it means
With each major weather disaster of recent years, there seems to have been a spate of major media stories about the enormous damage caused and the likelihood of a link to global warming, which is a mantra that is also beginning to be voiced by some of the world's large insuraces companies.  This study and others, however, disprove that linkage.  As the authors clearly demonstrate, it is we that are placing more property in harm's way, as more people and more societal infrastructure have become concentrated in disaster-prone areas.