The devastation of Hurricane Harvey marks a turning point and raises the terrible possibility that we’ve entered the age of climate chaos

Let there be no doubt: the horrific damage wrought by Hurricane Harvey was an almost entirely man-made catastrophe, one fingerprinted by all-too-human neglect, corruption and denial. If we needed a reminder of the power of water to destroy an American city, Hurricane Harvey provided it. In Houston, a fast-growing metropolis of more than 2 million people, it wasn’t the wind that was so damaging, or a storm surge pushing in – it was just water everywhere, falling for days in biblical torrents and transforming highways into rivers, flowing into homes, killing dozens, sending tens of thousands of people fleeing for higher ground. It was a terrifying and deadly display of what happens when nature collides with urban life on a planet radically altered by climate change.

Harvey is the worst rainfall event ever in the continental U.S. More than 50 inches of rain deluged parts of Houston. The amount of water that poured from the sky is difficult to conceptualize. By some estimates, 19 trillion gallons of water fell in five days. That’s roughly a million gallons of water for every person in southeastern Texas. Harvey’s economic toll will likely exceed Katrina as the most expensive disaster in American history.

Hurricanes are nothing new in Texas. In 1900, a hurricane hit Galveston, causing 15-foot storm surges, killing an estimated 8,000 people. But given what scientists know now about how rising CO2 levels impact the climate, it’s wrong to dismiss Harvey as a purely “natural” event.

First, thanks to increasing carbon pollution, the waters in the Gulf of Mexico, over which Harvey formed, were about five degrees higher than average. “As the world warms, evaporation speeds up,” explained climate scientist Katherine Hayhoe. So on average, there is more water vapor in the air now to sweep up and later dump over land. Also, because hurricane winds are generated by the difference in temperature between the atmosphere and oceans, the warmer waters tend to intensify a hurricane’s gales.

Second, a warming climate fuels sea-level rise, which is the result of the thermal expansion of the oceans and the melting of glaciers. Higher seas mean bigger storm surges, which can be devastating (recall the destruction wrought by Hurricane Sandy). But when the seas are higher, it also means that it is more difficult to drain rainwater into the ocean. And that is what happened in Houston: The water had nowhere to go.