Over the years, scientists have found lots of evidence that hurricanes are becoming more dangerous as the planet heats up.
They are rapidly intensifying more often, dumping higher rainfall totals and even moving slower, all because the world’s oceans and atmosphere are hotter due to human activity.
Now, a new study has identified yet another connection to our warming climate: Hurricanes are maintaining their strength after landfall for much longer, and in turn, exposing populations far inland to damaging winds that they have rarely experienced before.
The researchers found that over the past 50 years, the time it takes for a hurricane to weaken after landfall has increased by 94%.
In the late 1960s, a typical hurricane would lose roughly 75% of its intensity in the first day after landfall. But today, that same storm would be expected to weaken by just 50% in the first 24 hours after landfall, the study found.
“Say, for example, I’m in Atlanta at about 380 km (~236 miles) inland. Fifty years ago, I would have experienced something like a tropical storm from a hurricane that made landfall as a Category 3,” said Pinaki Chakraborty, a professor at the Okinawa Institute of Science and Technology and a co-author of the study. “But now, I would experience a Category 1 hurricane, so there’s been a tremendous increase in the kind of destruction that can travel inland.”
The findings were published Wednesday in the scientific journal Nature, and add to the already large body of evidence showing that global warming is increasing the destructive potential of hurricanes.
The researchers analyzed data on landfalling hurricanes across the continental US from 1967-2018, and then used computer simulations to determine which variables are allowing these storms to maintain strength even over land.
What they found is that while some of the slowdown in hurricane weakening can be attributed to a shift in storm tracks, which seems to be pushing more storms to make landfall on the East Coast, by far the biggest factor allowing strong hurricane conditions to reach farther inland is the increase in sea surface temperatures.
To understand why, the scientists say its important to understand from what these storms draw their strength in the first place.
At their core, hurricanes are massive engines of wind and rain that are fueled my warm ocean temperatures and moisture, Chakraborty said.
As a storm passes over the ocean, it feeds off warm, moist ocean air. The hotter the air beneath a hurricane, the more moisture that air can hold and, therefore, the more energy available to strengthen the hurricane.
“The ocean supplies moisture to the hurricane, and the hurricane heat engine converts the latent heat in that moisture into intense winds and rains,” Chakraborty said.
But once a hurricane makes landfall and is no longer over the ocean, that crucial energy supply that fuels the storm is cut off, causing storms to weaken over land.
However, human emissions of greenhouse gases have superheated our oceans and atmosphere. In the last 25 years alone, the world’s oceans have absorbed the heat equivalent of 3.6 billion Hiroshima bomb explosions, according to one study’s estimate.
All of this extra warmth means that hurricanes are carrying more moisture than they were in the past, giving them extra fuel to maintain their strength even hundreds of miles inland, and also explains why they’re dumping more rainfall.
The findings show that while hurricanes typically pose the greatest threats to developed coastlines, cities and towns hundreds of miles from the coasts are also increasingly finding themselves in harms way as the planet warms.
“The authors make a convincing case with simple numerical simulations that the increased water vapor carried by the storms is the main culprit for the slower decay rates over land,” said Jim Kossin, a climate scientist at NOAA’s National Centers for Environmental Information. “The impacts are clear: If hurricanes dissipate more slowly as they move over land, the damage they cause will almost certainly increase.”
The record-breaking 2020 hurricane season has offered plenty of examples that climate change is supercharging hurricanes like never before, and increasing the damage they’re capable of.
Hurricane Zeta, in particular, showed signs of this slower decay that the researchers outlined. By the time the storm reached New Jersey, it was still packing 50 mph winds a day after making landfall hundreds of miles south on the Gulf Coast, and left millions without power from Louisiana to Georgia and through the Carolinas.
And while the researchers say we can’t draw conclusions based on any one storm, they say the overall trend line is clear: Hurricanes are packing a punch farther inland than in recent decades, and it is connected to human-caused global warming.
“This slowdown in decay will continue unless there are really substantial measures taken to curb global warming,” Chakraborty said. “These regions further inland that are not well-prepared for these storms – for good reason – may now have to get more prepared. But I don’t think we can really prepare our way out of this.”