Hurricanes Have Doubled Due to Global Warming, Study Says

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Chris Landsea, science and operations officer with the National Hurricane Center in Miami, Florida, said in an email that the paper is "sloppy."

He is a leading critic of studies that link increased storm intensity to global warming, saying historical data are too crude to determine long-term trends.

The same, he argues, is true for storm frequency.

"The doubling in the number of storms that they find in their paper is just an artifact of technology, not climate change," he wrote.

Airplanes and satellites outfitted with sensitive instruments to monitor tropical storms did not exist a hundred years ago. Aircraft began monitoring hurricanes in 1944, satellites about 1970.

Recent research by Landsea finds three to four tropical storms were missed before the mid-1960s. And one storm a year was missed from the 1970s to the 1990s.

"When one takes into account these missing storms, the upward trend disappears and large multiyear variations remain," he said.

According to Holland, however, the technological improvements cannot account for all the observed increase in tropical storms.

His new study accounts for three missed storms per year in the pre-satellite era, and a statistically significant increase is still present, he said.

"So, yes there's uncertainty, there's no doubt about that," Holland said. "But it doesn't change our conclusions."

Frequency Transitions

According to the study, the period from 1900 to 1930 saw an average of six Atlantic tropical storms a year, with four of those storms growing into hurricanes.

From 1930 to 1940, the annual average increased to ten, with five hurricanes and five tropical storms.

Then, from 1995 to 2005, the average number of storms increased to 15, with 8 hurricanes and 7 tropical storms.

Even 2006, which seemed mild in the wake of the record-breaking 2005 season, saw ten tropical storms, the authors note.

Holland likened the transition phases to a thunderstorm in the Rocky Mountains—the sun rises and warms up the clear blue skies for hours, and then suddenly a thunderstorm develops.

"That's a very good example, but what we're looking at is happening on the global scale," he said.

The most recent period has yet to stabilize, leading the authors to conclude there may be even more active hurricane seasons in the future, though other factors may dampen the storm activity.

"What I will say is there is no evidence that I'm aware of and nothing I can think of which indicates they are going to go back down," Holland said.

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