Hurricanes on rise, study says
The number of hurricanes that strike each year has more than doubled over the past century, an increase tied to global warming, according to a study released Sunday.
“We’re seeing a quite substantial increase in hurricanes over the last century, very closely related to increases in sea surface temperatures in the tropical Atlantic Ocean,” says study author Greg Holland of the National Center for Atmospheric Research in Colorado.
Working with hurricane researcher Peter Webster of Georgia Institute of Technology, Holland looked at sea records from 1855 to 2005 in a study published in the British journal Philosophical Transactions of the Royal Society A.
The researchers found that average hurricane numbers jumped sharply during the 20th century, from 3.5 per year in the first 30 years to 8.4 in the earliest years of the 21st century. Over that time, Atlantic Ocean surface temperatures increased 0.65 degrees, which experts call a significant increase.
The study also shows that years with more hurricanes didn’t coincide with changes in the way storms are measured, says hurricane researcher Kerry Emanuel of Massachusetts Institute of Technology, who was not part of the study. “This makes it very unlikely that these upward jumps are owing to changing measurements and suggests that they are real.”
The extent to which this can be blamed on human activities that contribute to global warming has been the subject of scientific debate over the past two years, spurred by Hurricane Katrina’s destruction of New Orleans.
The new study drew criticism from experts who dispute the merits of combining data from the late 19th and early 20th centuries, when hurricane-tracking satellites didn’t exist, with statistics gleaned from more modern technology.
“They’re saying there’s a long, upward trend of the last 100 years in tropical storms. All the data I have looked at show that’s not the case,” says scientist William Gray, head of the Tropical Meteorological Project at Colorado State University.
The study notes that while 2006 was considered a quiet year for hurricanes, with five storms, 100 years ago it would have been considered a very stormy year and 20 years ago it would have been an average year. “We’ve seen the average become our bottom number for hurricanes,” Holland says.