What was done
In the words of the author, "records of extremely damaging storms in the United States during the years 1949-2006 were assessed to define their temporal distribution," where such storms were defined as those producing losses greater than $100 million, with a special subset defined as those producing losses greater than $1 billion.

What was learned
It was clearly evident from the pertinent data, according to Changnon, that "the number of storms at both loss levels has increased dramatically since 1990." The intriguing question, however, is why.

What it means
In discussing the results of his study, the University of Illinois geographer says there are four possible explanations for them. First, he notes that "storm measurement and data collection have improved over time." Second and third, he says "the increases may also reflect natural variations in climate or a shift in climate due to global warming." And he says that "a fourth reason is that society has become more vulnerable to storm damages." At the end of his analysis, therefore, the intriguing question remains unanswered, though hotly debated (see Hurricanes (Atlantic Ocean - Global Warming Effects: Frequency, The Past Century), as well as Storms (North America), in our Subject Index).