Harvey and climate change

Excellent column from Dave Leonhardt:

Even before the devastation from Harvey, southeastern Texas was enduring a year unlike any before.

The daily surface temperature of the Gulf of Mexico last winter never dropped below 73 degrees. You can probably guess how many previous times that had happened: Zero.

This sort of heat has a specific effect on storms: Warmer weather causesheavier rainfall. Why? When the seas warm, more moisture evaporates into the air, and when the air warms — which has also been happening in Texas — it can carry more moisture.

The severity of Harvey, in other words, is almost certainly related to climate change.

Yes, I know the sober warning that’s issued whenever an extreme weather disaster occurs: No individual storm can be definitively blamed on climate change. It’s true, too. Some version of Harvey probably would have happened without climate change, and we’ll never know the hypothetical truth.

But it’s time to shed some of the fussy over-precision about the relationship between climate change and weather. James Hansen, the eminent climate researcher, has used the term “scientific reticence” to describe this problem. Out of an abundance of academic caution — a caution that is in many ways admirable — scientists (and journalists) have obscured climate change’s true effects.

We don’t display the same fussiness in other important areas. No individual case of lung cancer can be definitively linked to smoking, as Heidi Cullen, the chief scientist at Climate Central, notes. Few vehicle accidents can be definitely linked to alcohol, and few saved lives can be definitively linked to seatbelts…

Yet smoking, drunken driving and seatbeltless riding each created a public health crisis. Once the link became clear and widely understood, people changed their behavior and prevented a whole lot of suffering.

Climate change is on its way to becoming a far worse public health crisis than any of those other problems. Already, it has aggravated droughts, famines and deadly heat waves. In the United States, global warming seems to be contributing to the spread of Lyme disease.

So, did climate change cause the devastation of Harvey?  Well, in the sense that basic science and logic tell us it almost certainly made it worse.

Also like Drum’s take:

Once in 500 years? Hmmm. Here are a couple of relevant illustrations from the Fourth National Climate Assessment, which was recently made public…

Down on the Gulf Coast, the number of “precipitation events” that exceed the largest amount expected over five years has already gone up 40 percent since 1901. By about 2030, what used to be a 5-year event around Houston will occur every two months. This means that Hurricane Harvey used to be a 500-year event, but maybe not anymore. Maybe it’s now a 20 or 30-year event.

These kinds of extreme flooding events will increase thanks to (a) rising sea levels, (b) an increase in tropical storm intensity (though not frequency), and (c) greater rainfall from tropical storms.

And a related post:

I wrote about this yesterday, and naturally got some pushback. “Harvey is unprecedented because it got stalled by a front, not because of climate change,” said one tweeter. That’s true about the front, and of course no one can say that climate change “caused” the flooding. But you can say that climate change increased the probabilities. Maybe it made Harvey a little more intense. Maybe it increased Harvey’s water vapor content a little bit. Maybe it made the front a little bit stronger. Add it all up and climate change didn’t cause Harvey, but it probably made it a few percent more likely and a few percent worse than it otherwise would have been. And at the tail end of bell curves, a few percent can mean a lot. It can turn a 500-year event into a 30 or 50 or 70-year event. Multiply this by the entire country, where the probabilities average out, and you can say without a doubt that climate change will produce more drought, more wildfires, more intense storms, and more flooding.

That’s how this stuff works. No big weather event ever has a single cause, but climate change skeptics are unwise to hang their hats on that. Likewise, I think that climate change hawks are unwise to shy away from blaming climate change for individual events. Their fear, generally, is that you can’t prove the role of climate change in any single extreme weather event, and they don’t want to open themselves to charges of alarmism. That’s admirable, but maybe just a bit too precious.

So, why should this matter?  Safe to say there are some Americans out there (especiallly those of a political party not named here) that just don’t think climate change is a serious issue.  When 1000-year floods become <100 year floods, that’s a pretty serious issue.

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About Steve Greene
Professor of Political Science at NC State http://faculty.chass.ncsu.edu/shgreene

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