Credit Matt Stamey/The Gainsville Sun, via Associated Press
The 2016 hurricane season just shifted from sleepy to fierce.
Tropical Storm Hermine strengthened into a hurricane on Thursday, just in time to strike the coast of Florida — the first hurricane to hit that state in nearly 11 years.
As that storm moves up the Atlantic coast, two other storms had been threatening Hawaii, a state that rarely receives such visitors. And there are probably more to come before the season concludes at the end of November.
This is, in other words, the height of the season, that time of year when conditions are the most favorable for making cyclones — and for making coastal residents nervous. It is also the moment that puts on display much of what we know, and still do not know, about hurricanes, and what to expect as climate change progresses.
Much of this, so far, is normal. This season is shaping up within the forecasts from the National Oceanic and Atmospheric Administration, which predicted in May that, in the Atlantic, there was a 70 percent likelihood of as many as 16 named storms.
As many as eight of them, the agency said, could become hurricanes (that is to say, with winds of 74 miles per hour) and as many as four could be major hurricanes with winds of 111 miles per hour or higher.
So things are on track in the Atlantic. In the Pacific, however, there have been some unusually strong storms and busy seasons in recent years.
All of this activity comes after what some meteorologists and news reports have called a long hurricane drought, citing a nearly 10-year run without major hurricanes making landfall in the continental United States. While that is literally true by the definitions used by climate scientists, any discussion of a hurricane drought can seem insulting to people in the Northeast and along the Texas Gulf Coast, where the so-called Superstorm Sandy and Hurricane Ike caused billions of dollars of damage.
The efforts to detect a lull involve arbitrary line-drawing exercises, Robert E. Hart of Florida State University wrote in a recent paper with Daniel R. Chavas of Princeton and Mark P. Guishard of the Bermuda Institute of Ocean Sciences. A Category 3 hurricane at landfall is considered a major storm; Hurricane Ike, for all its destructiveness, missed that mark, and Sandy was not considered a hurricane by the time it struck but instead an extratropical storm.
Whether or not the definitions of hurricane drought should be changed, Dr. Hart said in an exchange of emails as he prepared for Hurricane Hermine to hit his home in Tallahassee, long periods without storms can foster dangerous complacency. “Memory fades about the prior events, and more people have never experienced one than before,” he said. (His home came through the storm without damage.)
When it comes to hurricanes and climate change, scientists are still trying to figure out what warming is doing now and will do later. “It’s a really tough problem,” said Gabriel A. Vecchi, a climate researcher at NOAA’s geophysical fluid dynamics laboratory in Princeton.
The issue might appear to be simple: Warmer oceans provide more energy for storms, so storms should get more numerous and mighty. But other factors have complicated the picture, he said, including atmospheric changes that can affect wind shear, a factor that keeps cyclones from forming.
Credit Joe Raedle/Getty Images
Kerry A. Emanuel, a climate scientist at the Massachusetts Institute of Technology, said the evidence suggested climate change would cause the strongest storms to grow even stronger, and to be more frequent. Unresolved questions surround the effect of warming on the weaker storms, but even those will dump more rain, leading over time to increased damage from flooding.
In the Pacific, and especially near Hawaii, there is some evidence that the tendency toward more storms and stronger storms is underway, Dr. Vecchi said.
Hiroyuki Murakami, an associate research scholar at the Princeton laboratory, said that the unusually active hurricane seasons for Hawaii were being caused mostly by subtropical warming that is part of the ocean’s natural variability, but that human-caused climate change was also having an effect. His recent research, he said, suggests that active hurricane seasons in the Pacific will grow more frequent under the influence of warming, though natural variability will still play a role in the record for any individual year.
Finding the strong telltale “signal” of climate change in events is challenging, Dr. Emanuel said, because there are relatively few storms to draw data from. “If we have our numbers right,” he said, “it will be very difficult to see a signal in the actual data for a long time.”
Still, he said, prudent risk assessment calls for expecting these theories to be proved right over time, and to prepare.
The fuzziness about whether hurricane patterns are changing does not undercut the overwhelming scientific consensus about climate change in general, Dr. Vecchi said. “There is no conflict between uncertainty about what global warming is going to do to hurricanes, and the reality of global warming and human activity being one of the drivers of global warming,” he said.
“Just because I don’t know what you had for lunch,” he added, “doesn’t mean you don’t eat.”
Any storm can do tremendous damage where it hits, depending on the strength of its surge and winds and flooding. And overdevelopment along the nation’s coastlines means that the cost of damage is bound to escalate.
A big part of preparing, Dr. Emanuel said, is overhauling the nation’s flood insurance system, which currently does little to dissuade people from living in hazardous areas.
A recent report from the Natural Resources Defense Council showed that many homes are rebuilt over and over after storms with money from the National Flood Insurance Program.
The owners of one Louisiana home that has flooded 40 times have received $428,379 from the program over time. More than 2,100 homes flooded more than 10 times and received payments from the program. The 30,000 most-flooded homes make up less than 1 percent of the five million homes in the program, but have received more than 10 percent of the claims paid since 1978.
“Climate change just makes it worse,” Dr. Emanuel said, and he predicted far greater property damage and rebuilding costs in years to come. The insurance problem, he said, “sets up for a string of Katrinas and Sandys as far as the eye can see.”