Scientists have been trying to come up with ways to weaken hurricanes since the 1940s. Nothing that has been tried so far has worked, but that hasn't stopped a virtual cottage industry of researchers from hatching the next big, bold proposal.
The latest idea, published in the August issue of the journal Atmospheric Science Letters, comes at it from a new angle and at an opportune moment: A study published last week in the National Academy of Sciences concluded that large, damaging hurricanes will happen with greater frequency as global temperatures climb.
Early efforts at hurricane modification involved "seeding" clouds in the eye of an established hurricane in an attempt to disrupt its core. The new plan calls for seeding low marine stratocumulus clouds in areas where hurricanes form—before they form.The idea is that droplets of seawater sprayed into the air by unmanned vessels would rise up into the atmosphere and increase the brightness of the clouds. The brighter marine clouds would then reflect more sunlight back into space.
With less of the sun's energy reaching the ocean, sea-surface temperatures would drop by several degrees. Since hurricanes gather strength from warm ocean waters, the scientists say the intensity of hurricanes could be reduced by one or two categories.
Two of the cloud-seeding study's authors, Alan Gadian, a senior research lecturer in the School of Earth and Environment at the University of Leeds in England, and John Latham, a cloud physicist at the National Center for Atmospheric Research in Boulder, Colo., said the seeding would take place over an area a couple hundred of kilometers wide. They said the plan could be feasible within a few years.
But the viability of the seeding plan is by no means certain. Hurricane experts say implementing it would involve huge economic, logistic and scientific challenges. It would also be controversial, because it involves geoengineering, where man tries to alter the atmosphere on a mammoth scale to eliminate or reduce potential negative impacts on people or property. Cloud brightening is also among the geoengineering methods proposed for combating rising global air temperatures caused by greenhouse gases.
As with any proposed geoengineering solution to climate change, cloud-seeding faces two big barriers: public perception and politics.
"There's more to this than a scientific idea," said Frank Marks, director of NOAA's Hurricane Research Division. "There has to be political will to do this across the board. That's daunting, to say the least."
Among the many details to be resolved in the new proposal is determining just what areas would be best for seeding.
"We have yet to establish which regions could produce deleterious consequences, and which would not," Gadian and Latham said in an email response to questions about their paper.
That's no minor sticking point.
"If you get it wrong and mess with the climate, it could be worse than hurricanes," said Hugh Willoughby, a research professor in the Department of Earth Sciences at Florida International University who has been studying hurricane modification proposals for decades.
"I try to keep an open mind, in spite of being a curmudgeon," he said. "But it's kind of naive to think it would work. I've seen a lot of these ideas."
Willoughby wrote the paper that killed off Project StormFury, the world's longest-running experiment in hurricane modification by the U.S. Navy and Department of Commerce in the 1960s through early '80s. Scientists thought that by seeding with silver iodide just outside a hurricane's eye wall, they could expand the storm's eye and thus weaken it. Willoughby showed, through the study of subsequent, unseeded hurricanes, that the changes observed in the seeded storms would have occurred anyway, and that the theory was deeply flawed to begin with.
The concept of making clouds brighter through seeding is plausible, Willoughby said, but he thinks it's impractical and unlikely to accomplish the goal of weakening hurricanes.
The ocean warms a little each day starting in late spring and continuing through summer, he said. Hurricane season officially runs from June 1 to Nov. 30, but several tropical storms formed in May this year.
"Brightening clouds around a hurricane can't help if the ocean is already warmed up," he said. "You would want to keep the tropical ocean cool. You would need to start in May, and you would need to be out there every day."
Plus, he said, clouds over the tropical ocean are widely scattered and move around. "There's not enough cloud cover to do it."