Did Climate Change “Cause” Harvey?

Scientists say no—but it did make the storm much, much worse.

Floodwaters from Tropical Storm Harvey surround homes in Port Arthur, Texas, Thursday, Aug. 31, 2017

Gerald Herbert/AP

Harvey is now, officially, the heaviest and most destructive rainstorm in our nation’s history.

Nearly 25 trillion gallons of water pummeled southeast Texas and Louisiana over the course of a week, totaling more than 51 inches in some places. About 13 million residents came under some type of flood watch or warning, and the storm displaced as many as 30,000 people, many of whose homes and businesses were utterly destroyed. The injury and death totals won’t be settled for days, maybe even weeks. In trying to process the scope of this unprecedented natural disaster, people understandably want to know how and why it happened—and, of course, what we can do to keep it from happening again. So, in our grief and desperation, we ask: Was it climate change? Is that what caused Harvey?

And the climate scientists respond by saying: It’s more complicated than that.

Climate scientists are by nature and training a cautious bunch, and in their admirable caution they can frustrate those of us who clamor for the psychological comforts of a simple answer. We want them to identify a single, villainous entity that we can blame for a calamitous weather event like Harvey, in hopes that we can rally together against that which has been named, collectively staving off a repeat performance. In the face of such suffering, hearing that “it’s complicated” can feel like overcaution bordering on evasion. But it’s not.

In fact, the scientific community’s resistance to easy answers right now is a long-overdue teachable moment. We need to listen very closely to what scientists are telling us. And then, just as soon as we’ve addressed the humanitarian crisis at hand, we need to start talking seriously about the complicated nexus of atmospheric causes and effects, meteorological conditions, and other factors implicated in a disaster of this scale. To attribute Harvey to climate change, and then just leave it at that, would be incomplete and therefore incorrect. But to avoid talking about climate change—to ignore the role that it played in making Harvey much worse than it might have been otherwise—would be incomplete, incorrect, and immoral.

Here are two things that climate scientists agree on. Warmer air has a greater “carrying capacity” for moisture. That is, it can hold (and eventually deposit) a lot more water than cooler air can. At the same time, warmer ocean waters often bring more intense storms—and as it happens, waters in the Gulf of Mexico have been unusually warm lately. Put these two uncontroversial facts together and you arrive at an equally uncontroversial prediction: Rising air and ocean temperatures increase the risk that when hurricanes and tropical storms occur, they will bring with them a greater chance of extended rainfall and extensive flooding.

With Hurricanes Harvey and Irma, tell our political leaders they must act on climate now

For a Harvey-like deluge to occur, though, a storm system needs to stay put over a given area instead of moving along at its normal rate of speed. This phenomenon, known as a block or a blocking pattern, occurs when a storm gets trapped between two high-pressure areas that end up pushing against it with roughly equal force—the storm gets stuck and hovers in place, possibly for days. We saw this in Colorado’s “superflood” in 2013, and we seem to be experiencing more and more of this pattern lately. Scientific unanimity hasn’t yet been reached in regard to what causes blocking patterns, but an increasing number of scientists believe the melting of Arctic ice may be involved.

Think of it this way: There have always been and always will be tropical storms, but global warming is making them wetter. Similarly, storms and hurricanes have always posed and will always pose a threat to coastal communities, but it’s very possible that global warming is encouraging these storms to stick around longer, and do more damage, before dissipating.

These statements were true before Harvey. What’s changed in the past week, of course, is that these truths have been made even more visible and palpable for Americans, bitterly and tragically so. In other parts of the world—where deadly flooding is just as terrible, but much more common—the connection between devastation and a warming planet has been firmly established in the public mind for years. In South Asia, flooding has killed more than 1,200 people this week in what experts and locals are calling the worst monsoon season in memory. On Tuesday alone, the city of Mumbai received nearly a month’s worth of rainfall in a single day.

It’s fine—and even appropriate—for scientists to balk when asked, point-blank, if climate change “caused” Harvey or some other disastrous weather event. Because it actually is more complicated than that. But within that complexity is a compelling argument for acknowledging the role that a warmer atmosphere is playing in this ongoing pageant of human misery—and an equally compelling plea for us to do whatever we can to minimize damage and loss of life. We may not have the power to stop storms, hurricanes, or flooding events from taking place. But if it’s within our power to make them less devastating in the future, how can we, in good conscience, decline to act?


onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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