Some years ago, I wrote that although global warming seems like it should make hurricanes worse, we can’t really say that it has. Until just a few decades ago, if a hurricane happened not to pass over human observers or equipment, we might not know it existed. It’s not that we have no data before that, it’s just not a complete picture. How can we compare “before” and “after” when we don’t have a full “before”? There are other complications, too.
Of course, as I pointed out, all that applies only if “worse” is taken to mean more frequent or with higher wind-speeds. Since the most dangerous part of a hurricane is always its storm-surge, which is unambiguously worsened by sea-level rise, another answer to the question is that yes, global warming does make hurricanes worse and is going to keep doing so as long as the seas keep rising.
In any case, I didn’t expect any of that to change any time soon–but it might have just done so.
The problem of inadequate “before” data is still there, but a team from Stony Brook University has just modeled Hurricane Florence as it would have been without anthropogenic climate change–essentially, they used the models used to forecast hurricane behavior, but altered the model so as to simulate an un-warmed world. Because the same computer system was used to forecast both the real-world hurricane and the counterfactual one, the reliability of the system can be checked simply by comparing the real-world forecast with the actual behavior of Hurricane Florence–the forecast was pretty good, as it turned out.
So, all of you who were under Hurricane Florence? It’s official. Those of you who saw the heaviest rainfall–you saw 50% more of it because of climate change. And if you live on the coast, the storm was about 50 miles wider when it made landfall than it would have been, so at least some of you were hit by a storm surge that would otherwise have passed you by.
Now, when I say “it’s official,” I don’t actually know whether there is any controversy around this approach. I don’t have an inside view of either climatology or meteorology, though I do have friends I may be able to ask. So we may have to wait a while to see how this is received, but so far it seems legit to me.
While we’re discussing new hurricane research, it seems there are two more variables to how “bad” a hurricane can be, and climate change looks to be making them both worse.
One is the speed at which storms travel. The slower a hurricane is moving, the longer it takes to pass over your house and the more hurricane you get. That was part of the problem with Harvey, which simply stayed put over Houston and rained for way too long. A study just published in the journal, Nature suggests that storms are, on average, getting slower, apparently because climate change is causing weakening of the air currents that move hurricanes along.
The other variable is how fast storms intensify. We’re used to tropical systems strengthening gradually over a period of days, so that if a tropical storm (wind speed no greater than 74 mph) is pointed at you and about a day away, you can go ahead and prepare for a tropical storm, or possibly a category 1 hurricane. But occasionally a storm will undergo “rapid intensification” and you can go to bed prepared for that tropical storm and wake up to find a cat 4 bearing down on you. Scary, no?
And while nobody is actually sure yet how rapid intensification works, it does seem to be happening more and more often. A recent computer simulation shows that climate change does indeed result in more of the most severe hurricanes (categories 4 and 5) and does so specifically by making rapid intensification more frequent.
So, there you have it, folks. While I’m sure more research needs to be done (doesn’t it always?) and the picture will get clearer and more sure as we learn more, climate change is making hurricanes worse. That means worse in the future and it means worse already.
So when I say we all need to vote for climate-sane candidates willing to re-instate Paris? This is why.