Researchers at Colorado State University say the devastation caused by Hurricane Sandy in October was not caused by human-induced climate change.
In a recently released paper discussing the unusual “super-storm” that devastated the New Jersey shore and flooded the New York City subway and a traffic tunnel, CSU researchers William Gray and Phil Klotzbach say the influence of human activity on the formation and intensity of Atlantic hurricanes “is likely to be negligible.”
“As extensive and tragic as Sandy’s spawned destruction has been, it is not beyond the range of what is known about the variability of rare but extreme cyclone events,” Gray and Klotzbach wrote.
The researchers acknowledge that human activity has led to an increase in carbon dioxide being released into the Earth’s atmosphere and an increase in average temperature. But Gray and Klotzbach do not think that has caused more frequent and powerful hurricanes to form.
“Our hurricane research extending over many years indicates that Atlantic hurricane variability is driven almost exclusively by natural changes,” they wrote.
Gray, who has been studying hurricanes since the 1960s, was a pioneer in long-range hurricane forecasting. He determined that fluctuations in the salt content of ocean water — a naturally occuring cycle — affect the frequency with which hurricanes form.
When the salt content is high — as it is now in the Atlantic Basin — ocean water is warmer. Hurricanes draw their power from warm ocean waters, so the increase in salinity can lead to a corresponding increase in the number of hurricanes that form each summer.
Cycles of increased hurricane formation can last 20 years or more. Gray has said that a period of increased hurricane activity began in the Atlantic Ocean, Caribbean Sea and Gulf of Mexico in 1995.
Hurricane Sandy, which began as a tropical depression deep in the Caribbean Sea on October 22, morphed into a giant “perfect storm” as it pounded its way up the Atlantic Coast. On October 29, an unusual configuration of the jet stream and the position of a high pressure system to the north gave Sandy a powerful boost of energy and caused it to take an unusual track. The storm caused catastrophic destruction on the New Jersey shore and sent a storm surge of more than 13 feet into New York City.
The costs of Hurricane Sandy are still being added up, but the final total is expected to exceed $50 billion. Still, conclusions that Sandy and other extremely powerful and destructive storms were caused by climate change are mistaken, the CSU researchers said.
Gray and Klotzbach noted that 216 tropical storms formed during the 57 years from 1899 to 1955. By comparison, only 185 tropical storms formed during the 57-year period between 1956 and 2012, when the carbon dioxide content of the atmosphere was higher.
If increased carbon dioxide levels cause more hurricanes to form, then the number of storms from 1956 to 2012 should have exceeded the number from 1899 to 1956, the researchers conclude.
Willie Drye has been writing about hurricanes and other topics for National Geographic News since 2003, and he is currently writing a book about the Florida land boom of the 1920s. Follow his blog, Drye Goods.