Yes, I'm Going There: Harvey And Climate Change

Global warming didn't cause Hurricane Harvey. But scientists
are beginning to look at whether climate change might
have influenced this mega-disaster.

As I mentioned yesterday, some people tell me it's unseemly to talk right now about whether Hurricane Harvey was influenced by climate change.  

We're still trying to save lives and help people begin to pick up the pieces, like my friend George Quenzer, a meteorologist who lost his home and belongings in the flood.  Shouldn't we focus on that?

Well,  yes, of course, but Americans can walk and chew gum at the same time.

We can give all the aid we can to people in Texas and Louisiana who need our help.  And we can begin the process of learning from Harvey, and whether any part of the calamity was a result of climate change.

We know Harvey wasn't entirely the fault of climate change, but it might have altered the storm enough to make it worse.

Here's how climatologist Michael Mann puts it in his article this week in The Guardian:

"While we cannot say climate change 'caused' Hurricane Harvey (that is an ill-posed question) we can say that it exacerbated several characteristics of the storm in a way that greatly increased the risk of damage and loss of life. Climate change worsened the impact of Hurricane Harvey."

HARVEY STRENGTHENED ODDLY

Harvey came ashore as a Category 4 storm, packing winds of over 120 mph. As you can imagine, these winds were devastating to the area hit by the storm's eye, especially around Rockport and Port Aransas, Texas.

It was stronger than your average hurricane, but it wasn't the strongest ever. This powerful a storm has happened before, with or without global warming. The fact that Harvey was strong is not proof in and of itself of global warming.

Still, it's possible, but not certain, that climate change influenced Harvey's strength. Sea surface temperatures in the Gulf of Mexico were a little warmer than average in the path of Harvey. Hurricanes feed on warm water. The warmer the better.

As climatologist Michael Mann pointed out in The Guardian, the Gulf of Mexico is warm down to unusually deep depth, which probably helped fuel Harvey.  Such deep layer warmth in ocean water is a sign of climate change

One of the unusual aspects of Harvey is that it continued to strengthen right up to the time of landfall. Almost all hurricanes level off or even weaken just before hitting shore. An Atlantic article by Robinson Meyer suggested the unusual depth of warm water in the Gulf contributed to Harvey's strengthening trend that continued right up to the moment it hit land.

HARVEY STALLS

What made Harvey such a calamity is the fact that it stalled over Texas, unleashing an unrelenting firehose of downpours on areas from Houston to Beaumont and beyond.

Homes almost entirely submerged by Harvey

Again, hurricanes and tropical storms can and do stall, with or without global warming.

This was a case of incredible bad luck. If a hurricane stalls way out over the ocean, who cares? If it stalls near Houston, America's fourth largest city, it's worse than terrible.

It's unclear whether steering currents are slower in a warmer world. Scientists are debating this, and discussing to what extent slower atmospheric steering currents might be influenced by global warming.

But if steering currents are slowing in the atmosphere, that would increase the number of extreme weather events.

If a wet storm of any sort moves right along in a fast atmospheric flow, it's not a big deal,  becaue the rain won't last all that long. If the same storm stalls over one area, it's a disaster. That's why the science of understanding atmospheric patterns and flows in a warmer world is a priority for climate scientists.

HARVEY'S RAINS SUPER-INTENSE

Rainfall rates during Harvey were incredible.  At the peak of the downpours in Houston, a half inch of rain fell in just three minutes. Never heard of anything like that before.

The 26 inches of rain that drowned Beaumont Texas in one day included an incredible eight inches of rain in just one hour. (For perspective, here in Vermont, it normally takes two months during the summer to accumulate eight inches of rain.)

As Friederike Otto wrote in Climate Change News:

"In a warming world, the vapor capacity of the atmosphere increases and more extreme rainfall, like Texas is witnessing right now, is to be expected as a result. This leads many to conclude that climate change exacerbated the impacts of Hurricane Harvey."

I will add a caveat: The increased capacity of a warming atmosphere to hold more moisture and unleash incredible downpours is not proof that Hurricane Harvey was worse than it otherwise would have been.

It's hard to tease out exactly how climate change affects individual storms. But this is something scientists will study in Harvey.

Land use patterns probably worsened the Texas flooding, too. Houston sprawled out incredibly over the decades, and miles upon miles of land are paved over. This used to be land that could absorb much of the water from downpours, minimizing flooding.

Now, with the concrete and pavement, the water has no place to soak in. So it floods neighborhoods.

Still, Harvey was yet another mega-flood in a new era that seems to bring more and more mega-floods. This was the fourth so-called 100 year flood in Houston in three years.

Even as Houston was drowning this week, the worst flooding in decades was striking parts of India, Nepal and Bangladesh.

Another flood in Yemen this week killed at least 15 people.

Other parts of the nation have also had huge, catastrophic floods in recent years. Like Baton Rouge last August. North Carolina with Hurricane Matthew last October. The deluge in South Carolina in 2015. I could go on and on.

Only a handful of climate deniers can't accept the fact that global warming is happening. Scientists understand the concept more than ever and research is continuing at a sonic-boom inducing pace.

However, as Hurricane Harvey demonstrates, we still need to learn a lot more about climate change. Our lives might end up depending on it.