Study: Scientists See Natural Ocean Cycles As ‘Dominant’ In 2017 Hurricane Season

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Michael Bastasch DCNF Managing Editor
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  • A new study found warm Atlantic Ocean sea surface temperatures drove the increase in major hurricanes.
  • “[W]e speculate that the influence of natural variability on major hurricanes was dominant,” a scientist said.
  • Human activities could have played a role, but it’s likely smaller than natural variability, the scientist said.

Natural variability, not man-made global warming, was likely the “dominant” factor behind the slew of major hurricanes that churned in the Atlantic Ocean in 2017, according to a study.

The study, published in the journal Science on Thursday, found the “increase in the 2017 major hurricanes was not primarily caused by La Niña conditions in the Pacific Ocean, but mainly by pronounced warm sea surface conditions in the tropical North Atlantic.”

“The key factor controlling Atlantic major hurricane activity appears to be how much the tropical Atlantic warms relative to the rest of the global ocean,” reads the study. (RELATED: Scientists Throw Cold Water On Claims Linking Hurricane Florence To Global Warming)

While models suggested any future warming in the Atlantic Ocean would increase the risk of major hurricanes, the study’s authors suspect natural ocean cycles played a dominant role in 2017’s active hurricane season.

“The effect of anthropogenic warming is very slow,” the study’s lead author Hiroyuko Murakami told The Daily Caller News Foundation.

“On the other hand, natural variability like Atlantic Meridional Mode (AMM) and Atlantic Multidecadal Mode (AMM) exerts significant fluctuations for sea surface temperature over the tropical Atlantic Ocean,” said Murakami, a scientist at the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory.

“Given the high positive values for the AMM and AMO indices for the 2017 summer, we speculate that the influence of natural variability on major hurricanes was dominant,” Murakami told TheDCNF via email.

The 2017 Atlantic hurricane season was an active one. Seventeen named storms churned in the Atlantic, Gulf of Mexico and Caribbean Sea, including six major hurricanes. However, the heightened activity came after several years of relatively depressed hurricane seasons in terms of accumulated cyclone energy (ACE), a measure of hurricane intensity.

Hurricanes Irma and Maria ripped through the Caribbean with maximum sustained winds of more than 170 miles per hour, causing billions of dollars in damage. Maria devastated Puerto Rico, taking out the electric grid.

Hurricane Harvey set rainfall records over the greater Houston area when it struck the Texas coast in August 2017. Harvey stalled over the region for days, causing devastating flooding.

Harvey was estimated to have caused $125 billion in damage, and several studies have tried to pin the storm’s heavy rains on man-made global warming. Those studies, while flawed, attracted media attention.

Murakami said global warming and aerosols from industrial activities could have also played a role, but it’s difficult to tell. He said more study and observations are needed to separate out any impact human activities may have had.

“The reason why it is difficult to separate these effects is because of the significant variations caused by the natural variability,” Murakami said.

“If we had a long-term observations, we could have separated them,” he said. “But availability of reliable long-term observations is limited. It is possible to estimate these effects in a model world using a large number of climate simulations. Further study is needed.”

University of Miami hurricane researcher Brian McNoldy, who was not involved in study, also cautioned against linking the 2017 hurricane season to global warming.

“It is true that a warmer ocean can support stronger hurricanes, but I think we need to avoid linking climate change to specific storms, seasons, and basins,” McNoldy told The Washington Post.

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