WASHINGTON (AP) "A warmer world makes hurricanes worse, and scientists say they are more humid, more energetic, and more intense.
Their storm surges are more destructive because climate change has already brought the seas to the surface. And lately the storms seem to slow down more often and release more rain.
One study after another shows that climate change generally worsens hurricanes. However, it is not easy to determine the role of global warming in a particular storm such as Hurricane Florence or Typhoon Mangchut, at least not without detailed statistical and computer analysis.
The Associated Press consulted 17 meteorologists and scientists who are studying climate change, hurricanes, or both. A few experts remain cautious in ascribing global warming to a single event, but most scientists see the human hand in Florence.
Global warming has not caused Florence, they say. But it makes the system a bigger danger.
"Florence is another sign of the storms that are being charged by humans, and that are becoming more and more frequent and destructive as the planet warms," said Jonathan Overpeck, Dean of the Environmental School at the University of Michigan. He said the risk goes beyond the Atlantic Ocean, like the typhoon mangrove that hit the Philippines on Friday.
For a long time scientists would not make clear connections when asked about climate change and certain weather events. But in recent years, the new field of attribution research has allowed researchers to use statistics and computer models to calculate how events in a world without man-made climate change would differ.
A few months after Hurricane Harvey, studies found that global warming has significantly increased the chances of Harvey's record rain.
"It's a bit of a storyline from 'Back to the Future', where you travel back in time to an alternative reality that is plausible, but without people changing the climate, Peter Stott said the University of Exeter, one of the pioneers of the field.
A National Academy of Sciences report believes these studies are generally credible. A team of scientists tried to do a similar analysis for Florence, but external experts were cautious because it was based on forecasts rather than observations and did not use enough computer simulations.
As the world warms and science advances, scientists become more specific, even without attribution studies. They quote basic physics, the latest research on storms and past studies, and put them together for something like Florence.
"I think we can say that the storm is stronger, wetter, and more effective from the coastal flood point of view than from man-made warming," Pennsylvania State University climate scientist Michael Mann wrote in an e-mail. "And we do not need an attribution study to say that in my view, we just need the laws of thermodynamics."
Georgia tech climatologist Kim Cobb is not only concerned with basic physics, but with all peer review studies that combine climate change with wetter storms.
"We have solid data over decades of precipitation records to nail the attribution" Climate change is changing the frequency of extreme rains, "Cobb said.
Several factors make scientists safer when they point to the finger of climate change in Florence.
For every degree of air it warms, it can hold nearly 4 percent more water (7 percent per degree Celsius) and measurably offer more energy to gambit the storm, scientists said.
"The amount of water that comes from hurricanes is certainly the most robust compound we have," said National Oceanic and Atmospheric Administration climate scientist Jim Kossin.
And to take a closer look at Florence, "It is very likely that climate change has heated the ocean so that the heavy rains of the hurricane are more destructive than without global warming," said former hurricane hunter Weather Underground Meteorological Director Jeff Masters.
The warmer air and water also make storms more intense or stronger, Stott said.
A Kossin study this year showed that tropical cyclones "a category that includes hurricanes and typhoons" are slower moving and even faltering. Kossin said, "It happens much more than before." Several studies agree that climate change is guilty but slightly different in their conclusions.
With the emergence of Florence, a place in the US was soaked due to a hurricane for four consecutive years, said storm expert Hal Needham.
Kossin and Overpeck also pointed to studies that show that storms increase faster than they used to.
Just as in Superstorm Sandy, scientists said it is clear that hurricane storm surge is worsened by sea-level rise because the power of 6 to 10 feet of water comes on top of seas, which were much lower decades ago. An extra 8 inches or so can mean the difference between staying dry or damaged, Masters said.
In the Carolinas, natural and transient environmental factors added to the "onslaught" of global alarm. That's why the seas have risen nearly 5 inches in five years, said Andrea Dutton of the University of Florida.
Weathermodels.com meteorologist Ryan Maue warned observers should "be guided by global trends and not by individual cases."
Hurricane expert Brian McNoldy of the University of Miami said that there are too many factors that are constantly changing and making it difficult to blame climate change concretely.
"If you're trying to make a climate policy," Maue said Friday, "you do not want to do it on a storm-by-weather basis."
Follow Seth Borenstein on Twitter: @bornenbears. His work can be found here.
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