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Our First Solid Evidence For What Climate Change Did to Hurricane Harvey

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Hurricane Harvey appears to be just the beginning of what’s to come for Houston, and Texas as a whole. That’s according to a study published online Monday in the Proceedings of the National Academy of Sciences.

The relationship between climate change and hurricanes is a tricky one. We know that, generally, storms are more intense when the air is warmer, and their impacts on coastlines are more severe when the sea level is higher. But determining whether the odds of a single storm were affected by the warming climate is a science all unto itself. It’s called weather attribution.


Many researchers weren’t sure what to initially think about Harvey when it struck the Gulf in August. Nearly three months later, at least one scientist is offering some answers as to how much climate change impacted the odds of the hurricane that left at least 82 dead and damaged more than 119,000 homes in Harris County, Texas—and how much it’ll continue to boost those odds in the future.


Kerry Emanuel, an atmospheric science professor at MIT who authored the paper, found that record rainfall—like the 27 trillion gallons of water we saw with Harvey—will become 18 percent more likely to hit the state by the end of the century under a business-as-usual, worst-case-scenario emissions model, which Emanuel uses in the study.

Between 1981 and 2000, those chances were slim: 1 percent for a given year. When looking at Houston, specifically, he found that storms like Harvey have historically happened once every 2,000 years, describing it as “biblical,” in a press release.

Climate change is changing all that. It already is: Emanuel estimates that, in 2017, those 1 percent odds have increased to 6 percent.


“You’re rolling the dice every year,” said Emanuel, in the press release. “And we believe the odds of a flood like Harvey are changing.”

Most climate models available to scientists like Emanuel are too coarse in resolution to simulate the formation of hurricanes. But Emanuel and his team developed one that can model hurricanes at high spatial resolutions within a changing climate. At least one other scientist, atmospheric scientist Phil Klotzbach, at Colorado State University, knows and trusts this approach. He’s seen this model used in previous research by Emanuel, and “it seems to work fairly well at replicating overall Atlantic hurricane activity,” Klotzbach wrote in an email to Earther.


But we also know that Texas saw some unique conditions with Harvey that made the storm’s impacts so much worse. For one, Houston didn’t build with storms in mind. Its sprawling development and vast impervious surfaces allowed water to just pool in the city and create flooding like no one (well, except these journalists) expected.


Then, there were the meteorological conditions surrounding the storm itself. Atmospheric steering currents, which would usually bring a storm like Harvey inland to die, were unusually weak, so the hurricane stayed close to shore picking up more and more water from the Gulf with which to pound Texas.

That’s where Klotzbach has some questions: “How will steering current patterns change in the future?” he asked, in the email to Earther.


Emanuel ponders this, too, in his study. Still, in an email to Earther, he emphasized his confidence in his methods, which account for both storm movement and changing atmospheric moisture. And this study isn’t the last one coming. He and his team are analyzing how much of the state’s projected rainfall increases will result from either changing atmospheric moisture levels or longer-lasting events. “Preliminary results show roughly equal contributions from both factors,” he wrote to Earther.

Emanuel does know some things for certain, though. And he makes note in his study:

[A]nthropogenic climate change is expected to lead to a greater incidence of high-intensity hurricanes, which together with rising sea level, will produce increased risk of storm surge flooding, while hurricanes are projected to produce substantially more precipitation as the atmosphere and oceans warm.


While it’s difficult to say climate change caused any one storm, we can safely assume climate change will bring about more storms like Harvey, or Irma, or Maria. Research like Emanuel’s gives us a sense of how much more likely these storms will be in the future. And that information will help us prepare.