Hurricanes Have Doubled Due to Global Warming, Study Says

John Roach, National Geographic News
The number of Atlantic hurricanes that form each year has doubled over the past century and global warming is largely to blame, according a new study.
The increase occurred in two major steps of about 50 percent each, one in the 1930s and the second since 1995.
"It hasn't been a steady, gradual increase," said Greg Holland, a scientist with the National Center for Atmospheric Research in Boulder, Colorado.
The increases coincide closely with rises in sea surface temperatures in the eastern Atlantic tropics. Previous studies have attributed these rises to human emissions of greenhouse gases.
The study also shows that the proportion of major hurricanes to less intense hurricanes has sharply increased in recent years, which agrees with earlier studies showing an increase in stronger storms.
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.
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.