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.
