Warmer ocean temperatures appear to be fueling more intense hurricanes at the expense of the overall number of storms, says a new study published today in Nature Climate Change.
Over the past decade, studies have analyzed ad nauseam how warmer temperatures might be changing the annual number of hurricanes, or the maximum intensity. In theory, the hurricane hypothesis has always been a simple one: Tropical cyclones are fueled by warm ocean surface water, so warmer oceans should be fueling stronger hurricanes.
But in practice, the connection between hurricanes and climate change has been a hard nut to crack because of an equally simple caveat — we just don’t have enough years of good historical data to predict how hurricanes intensity or frequency might change in our warming future.
So hurricane researchers at Florida State University have turned the conversation on its head. Instead of examining how either the number of hurricanes is changing, or how the intensity is changing, they investigated how the relationship between frequency and intensity might be altered by warmer ocean temperatures.
The study came to an interesting conclusion — that warmer sea surface temperatures are pushing some hurricanes to be more intense at the expense of the overall number of storms. Since 1984 and the beginning the enhanced satellite imagery era, the strength of hurricanes as measured by wind speed has increased by 3 miles per hour, but there were 6.1 fewer cyclones than there would have been if ocean temperatures would have remained unchanged.
“We’re seeing fewer hurricanes, but the ones we do see are more intense,” said James Elsner, professor of geography at Florida State University and coauthor on the study. “When one comes, all hell can break loose.”
The physical reasoning for this tropical trade-off is that while warmer oceans provide more energy for hurricanes to utilize, it also creates an unfavorable mid and upper-level atmosphere for storms. So while the overall number of storms might be reduced because of the environmental hurdles they would need to overcome, the ones that do get going tend to be stronger.
The study’s authors say that their results might even be directly applied to seasonal forecasts, at least on a global scale. “In a warmer year, stronger but fewer tropical cyclones are likely to occur,” said Namyoung Kang, the lead author on the study and the deputy director of the National Typhoon Center in South Korea. “In a colder year, on the other hand, weaker but more tropical cyclones.”
Of course, stronger hurricanes tend to be much more life-threatening and destructive than weaker ones, though storms in recent years have begun to turn the table on what we consider to be a destructive cyclone. Hurricane Sandy in 2012 was just a category 1 as it made its left hook into the East Coast, but the sheer size of the storm created a surge that is typically associated with a much stronger storm. That category 1 storm did over $60 billion in damage, and was elevated to the second costliest storm on record behind Katrina.
Colorado State hurricane scientist Phil Klotzbach is forecasting a much quieter than average hurricane season in the North Atlantic this year, citing cooler than average Atlantic ocean temperatures and a strengthening El Nino, which tends to create an unfavorable environment for hurricanes in the Atlantic. NOAA typically releases its first seasonal hurricane outlook in late May.