Hurricane Harvey has already dumped 9 trillion gallons of water on Texas and may leave even more before it backs up to the Gulf of Mexico. Starting as a category 4 hurricane as it made landfall on Friday night, Harvey, which has since been downgraded to a tropical storm, is breaking weather records every hour—and is leaving some scientists scratching their heads as to why it stalled over south Texas instead of cruising northward to Oklahoma and then to the Midwest as storms of this nature typically do.

Is climate change to blame for its atypical path of destruction? Well, a bit, according to climate researchers.

Climate change didn’t spawn Harvey, or any other hurricane, though it has made them more dangerous. But scientists are careful not to blame all of Harvey’s destruction on greenhouse warming. Plus, this is a conditional situation: Houston's lack of rain-sponging green space and devil-may-care zoning laws—have probably made things worse as well.

NASA

“The hurricane is a naturally occurring hazard that is exacerbated by climate change,” says Katharine Hayhoe, an atmospheric scientist and professor of political science at Texas Tech University. “But the actual risk to Houston is a combination of the hazard—rainfall, storm surge and wind, the vulnerability, and the exposure." In Houston's case, vulnerability is particularly high. "It’s a rapidly growing city with vast areas of impervious surfaces," Hayhoe says. "Its infrastructure is crumbling. And it’s difficult for people to get out of harm's way.”

When Hayhoe and others scientists look at the storm itself, they see a hurricane that has been able to keep one foot on the gas pedal while still connected to the gas tank. Warmer water means more water vapor available to power the hurricane, and Harvey’s fuel source—the Gulf of Mexico—is unusually warm right now, thanks to a combo of slow climate change-related warming and a hot August in the gulf.

As Harvey approached the Texas coast last week, the Gulf ocean temperature rose 2.7 to 7.2 degrees Fahrenheit above average. “That provided a deep, warm pool of water used as fuel,” says Dalia Kirschbaum, a research scientist at NASA’s Goddard Space Flight Center who studies hurricane hydrology. Harvey used this hot spot to shift from a tropical depression to a category 4 hurricane in roughly 48 hours.

Long term, the sea surface temperature of that region has risen about 1 degree over the past few decades—from roughly 86 to 87 degrees Fahrenheit, according to Michael Mann, a climatologist at Penn State. Mann said in a Facebook post on Monday that a relationship known as the Clausius-Clapeyron equation tells us there is a roughly 3 percent increase in average atmospheric moisture content for each 0.5 degrees Celsius of warming—almost 1 degree Fahrenheit. That means 3 to 5 percent more moisture in the atmosphere in the Gulf region near the south Texas coast. So Harvey has a big tank of tropical moisture that it has been dumping on land.

The storm surge is also made worse by sea levels that are higher than they were decades ago. Thanks to climate change, storm surges today are seven inches higher than they were 30 years ago, according to a January study by NOAA—though other factors can combine to increase surges even more. By the year 2100, global sea levels will rise an average of 1 to 8.2 feet. But the western Gulf Coast will see an additional rise of 1 to 1.6 feet, according to the NOAA study.