Hurricanes that make landfall are maintaining their strength longer because of climate change, a new study suggests, meaning such storms could have more of an impact than in the past.
The reason storms are maintaining their strength, according to researchers at the Okinawa Institute of Science and Technology Graduate University (OIST), is the increase in sea surface temperatures.
A hurricane needs several things to form, the main one being warm water. When warm, moist air rises from that water, it's replaced by cooler air which in turn warms and rises. Clouds form and then, under the right conditions, begin to rotate with the spin of Earth. Given enough warm water, the cycle continues and a hurricane forms.
It's well understood that, because of climate change, ocean temperatures have risen. According to the latest report from the Intergovernmental Panel on Climate Change, between 1971 and 2010, sea surface temperatures rose by roughly 0.11 C and will continue to rise as the oceans take up roughly 90 per cent of the excess heat produced by a warming climate.
All of that translates into more fuel for hurricanes. And that means it takes hurricanes longer to run out of gas as they move inland.
"Fifty years ago, for a hurricane to decay [once it made landfall], it took 17 hours. Now, if the landfall is at the same intensity and every other thing is the same … it would take 33 hours," said Pinaki Chakraborty, a professor of fluid mechanics at OIST and co-author of the study, published in the journal Nature Research on Wednesday.
"So the time has almost doubled. Meanwhile, the hurricane is of course traveling inland, which means larger and larger areas are affected."
Anya Waite, a professor at Dalhousie University in Halifax and the CEO and scientific director of the Ocean Frontier Institute, says the findings don't surprise her too much, since it's well-known the role sea surface temperatures play in fuelling hurricanes. But, she said, it is something that Canadians will have to consider to prepare for the effects of climate change.
"We need to worry about risk further and further inland, as the ocean warms up," Waite said. "And that's scary because we're already worried on the coasts
"Now we have to worry that the line that we draw inland goes a lot further. That means that rainfall and wind and other effects and hurricanes are going to go into New Brunswick and much further inland than ever before."
Climatologist Michael Mann, a professor of atmospheric science at Penn State University, says the findings are interesting, and that he looks forward to more followup.
The findings require "rigorous modelling efforts to establish the underlying mechanisms," he wrote in an email. "Since flooding is the major cause of death and destruction from landfalling tropical storms, this study suggests the potential for even greater risk than has been established in past studies."
"I would most definitely think that many of the things that we are putting here, may very well be thoroughly revised over time," he said. "This is just a very first step onto something that was somehow missed in all the analysis done before. So I'm hoping more people will get interested."
Climate change and hurricanes
The effects of climate change on hurricanes isn't entirely clear, though the science is beginning to reveal more.
"What we know is that hurricanes are going to be bigger, stronger, and move longer distances as the ocean warms," said Waite. "And we also know that our contribution to that ocean warming is significant: the oceans absorb up to 50 per cent of the heat that we generate, and that is generated through climate change and through the greenhouse effect. So it's really a direct action that we can expect from our activities as greenhouse gas polluters."
While the 2020 hurricane season has been the busiest on record, with 30 named storms as of Tuesday, that is likely due to the influence of La Nina, a cooling of the ocean in the east Pacific that can have global effects.
Not all hurricanes make landfall, and less than half have this year.
"The most intense hurricanes did not make landfall," Chakraborty said. "And therefore, we have been lucky that the terrible effects of climate change are not communicated via hurricanes to us."
Rising ocean temperatures mean that more inland cities need to reconsider their planning in the face of climate change, he says.
Stronger hurricanes also mean more challenges for coastal communities.
"We can certainly look to our coasts intelligently. We can move our houses from the shoreline, which is very hard because we're emotionally attached to the shoreline; we don't want to let go of our cottage on the rocking outcrop," said Waite. "But if we don't do that then the insurance companies are going to be under stress. Because, who's going to pay for a flooded home?"
And that extends inland.
"[In the past] pretty much a day after the hurricane hits land, it's over," said Waite. "It could get as far as Ontario in a very, very unusual case."
But the new study shows that with warming ocean waters, that is set to change.
"Whereas now … you get several days of activity after leaving the ocean. That's really serious for us."