Hurricanes And Climate Change — An Explainer

After wrecking large swaths of the northwestern reaches of the Bahamas, leaving at least 30 dead and a nation in crisis, Hurricane Dorian is currently making its way up the east coast of the United States. Emergency alerts have gone out for the entire South Carolina coastline; Charleston has seen flooding, high winds, and downed power lines; North Carolinians are being told to shelter in place; and experts are forecasting storm surges and possible flash flooding in coastal North Carolina and Virginia through Friday evening, with predicted rainfall of “6 to 12 inches in the coastal Carolinas and 3 to 8 inches in far southeast Virginia.”

Though the destruction wrought by hurricanes isn’t new by any stretch of the imagination, over the past decade, we’ve collectively witnessed storms like 2012’s Hurricane Sandy, which damaged or destroyed 650,000 homes, left 7.5 million people without power, and led to over 285 deaths, or 2017’s Hurricanes Harvey and Maria, the latter of which plunged Puerto Rico into darkness, and is estimated to have caused at least 2,975 deaths. Irma and Jose also did a fair amount of damage in 2017. Last year, Florence and Michael brought punishing rains to the Atlantic coast as part of a 22-hurricane season that “began earlier, continued later, and some took unexpected paths before hitting land.” Five of the 35 recorded category 5 hurricanes in 169 years of record-keeping have occurred in the past four years.

So what gives? Is this just Mother Nature flexing her muscles? Part of shifting and completely normal trends? Bad luck? Or is an influx of powerful hurricanes linked to climate change? We break it down.

What happened in the Bahamas?

First: let’s go over what’s going on with Dorian, the most recent hurricane to form in the Atlantic Ocean.

As of the morning of Friday, September 6, Dorian seems to be widening and weakening along the coast of North Carolina. But before Dorian made its way up the east coast of the U.S., it first made landfall in the Abaco Islands — an outcropping of smaller islands in the Bahamas populated by fishermen and Haitian immigrants — as a category five storm early on Monday, September 2. It then stalled out over Grand Bahama, the popular tourist island, for an entire day, pummeling the island with “sustained winds as high as 180 miles per hour.”

Of the damage to the Abacos, Lia Head-Rigby, who runs the hurricane relief group HeadKnowles, told the Associated Press, “It’s total devastation. It’s decimated. Apocalyptic.” The death toll in the Bahamas is at least 30, but expected to rise in the coming days and weeks as rescue efforts get underway.

The storm moved toward Florida on Tuesday, September 3, and, though it’s now hovering between a category two and three storm, it’s making its way up the east coast of the U.S. with a substantial forecast cone, which effectively means: while they can guess, experts can’t say exactly where it’ll go next.

Was climate change a contributing factor to the intensity of Hurricane Dorian?

Maybe, according to Tom Knutson, a research meteorologist at the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory. Knutson researches the intersection between tropical cyclones (hurricanes) and climate change, so he would certainly know.

And while Knutson is careful not to make assumptions about what caused something as complicated as a hurricane — which depends on a multitude of factors, from sea surface temperatures to the amount of moisture in the air, to variables in wind shear — he’s quick to point out promising research from colleague Jim Kossin about what the human-caused warming of the planet could be doing to the speed of storms. There’s preliminary evidence that, as the atmosphere warms, it slows down atmospheric circulation, which, in turn, causes storms such as hurricanes to slow down. These stall-outs can cause extensive damage if they happen when the storms make landfall — and that is precisely what happened in the Bahamas. Dorian stayed put over the Bahamas for almost two days.

“Potentially it’s another way in which climate change could lead to greater impacts on people,” Knutson says, “because if storms start slowing down, they can hang around longer, rain longer. As is the case with Dorian, [hurricanes like that] just hang around longer with high winds, and cause more damage that way.”

So wait, does climate change have anything to do with hurricanes?

This is a loaded question with a complicated answer. The simple version is, “yes.” Many experts believe climate change is creating certain conditions that could be conducive to larger, more destructive storms. Still, the evidence to support climate change’s impact on hurricane patterns isn’t as clear as, say, the evidence showing that global warming is largely anthropogenic.

Here’s what we mean.

Human-caused global warming has caused the earth to warm by approximately 0.8 degrees celsius (1.4 degrees Fahrenheit) and the sea surface to warm by approximately 0.55 degrees celsius (1 degree Fahrenheit). We can say this definitively. (It’s also worth noting that, though these numbers may seem low, scientists at NASA stress that a one to two degree drop in temperature was enough to plunge the earth into the Little Ice Age, and a five-degree drop “was enough to bury a large part of North America under a towering mass of ice 20,000 years ago.”)