Hurricane Harvey was ‘almost certainly’ more devastating because of human-caused warming

• Climate change was not the cause of Hurricane Harvey, but there's reason to think a warmer planet can make such storms more devastating.
• "Harvey was almost certainly more intense than it would have been in the absence of human-caused warming," said one scientist.
• Understanding the effects of climate on storms can help us better prepare for them in the future.

Climate change didn't cause Hurricane Harvey. But scientists can say it likely made the storm worse, according to Michael Mann, a distinguished professor of Atmospheric Science at Penn State.

As the storm swirled and took shape in the Gulf of Mexico, warmer-than-normal waters allowed the weather system to absorb more moisture than it otherwise would have. That led it to drop an unprecedented amount of rain over Texas — some areas are expected to have up to 50 inches by the time the storm is over.

Additionally, higher sea levels — due to climate change and to human disturbances like oil drilling that have changed the sea and land levels — created more devastating flooding as the storm caused waters to rise.

"Harvey was almost certainly more intense than it would have been in the absence of human-caused warming, which means stronger winds, more wind damage, and a larger storm surge,"Mann wrote on his Facebook page.

How climate change and human activity make storms hit harder

There's nothing new about hurricanes hitting the Gulf and Atlantic coasts, as climate scientist Katharine Hayhoe said on Twitter. Hurricanes are natural and their causes are complicated.

But a recent draft of a major government report on the state of the climate (which Hayhoe contributed to) noted that a warmer climate increases ocean temperatures, raises sea levels, and creates more atmospheric water vapor — which makes heavy precipitation events more likely.

Harvey and other hurricanes are exacerbated by these factors, Hayhoe said. That's why meteorologists were so concerned about this storm as it approached the coast.

"If you look at the ocean temperatures in the Gulf of Mexico, they're at near-record warm levels, about 87 Fahrenheit underneath Harvey right now, that's about 2 degrees Fahrenheit above average for this time of year. That's a lot of extra heat energy available to evaporate water vapor into the air," Jeff Masters, a meteorologist at The Weather Company who cofounded the weather-data website Weather Underground, told Business Insider on Thursday.

As Harvey picked up more moisture, it rapidly strengthened from a tropical storm to a category 4 hurricane before making landfall, after which it stalled as a tropical storm, dumping so much rain that the National Weather Service had to add more colors to its map.

Harvey has been described as a once-in-500-years-event, though some spots could hit the once-in-a-million-years benchmark. But such events seem to be becoming more common, as evidenced by major recent storms like Allison in 2001, Rita in 2005, and Ike in 2008. By some definitions, the Houston area faced 500-year floods in both 2015 and 2016. 

As ProPublica and the Texas Tribune reported in 2016, the way that we've traditionally calculated how rare these events are may no longer be valid, largely because of climate change.

"Houston's perfect storm is coming — and it's not a matter of if but when," the authors of that story wrote. One researcher told ProPublica that more people die from floods in the Houston region than anywhere else.

ProPublica and the Texas Tribune pointed out that Houston doesn't have enough regulations in place to mitigate flood risk, and that prairies that used to absorb water have been paved over. For these and other reasons, Houston was ill-prepared for a major storm.

And a recent executive order by the Trump administration rolled back Obama-era regulations that would have required new infrastructure built in flood-prone regions to be climate resilient. So Houston and other cities won't have to take such factors into account when considering future development. 

Why this matters

Some argue that it's too soon to talk about whether climate change contributed to the ongoing Harvey situation, or suggest that doing so politicizes the event.

But the evidence we have indicates that climate is likely to have had an effect on the severity of the storm, as did human development and other factors. And understanding those things is vital for future preparation.

As Hayhoe said on Twitter, scientists care about the way that climate affects hurricanes because climate change can make storms stronger and more devastating. Action on climate (or lack thereof) could therefore make a difference for people vulnerable to storms like this in the future. One of the reasons the Department of Defense cares so much about climate change is because severe weather can have a big impact on human lives.

That's not about politics, it's about preparation.

Right now, of course, the most important story is what's happening to people in southeast Texas and what's being done to help those suffering in the storm.

But as meteorologist Eric Holthaus said on Twitter, understanding the effects humans have on climate is important, both now and in the future.

Rebecca Harrington contributed to this post.

SEE ALSO: There's a 95% chance the world will warm beyond a crucial tipping point — here's what that means

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