As I write this, Hurricane Irma is bearing down on the continental United States. This storm is a monster, truly terrifying. It is a Category 5 hurricane, the highest rating on the Saffir-Simpson wind scale: Although variable, it has had sustained winds of nearly 300 kilometers per hour (185 mph). That’s equivalent to an EF4 tornado, powerful enough to tear roofs off houses and completely demolish some smaller structures.
It sustained that wind speed for a day and a half, breaking the previous duration record, and is the strongest Atlantic hurricane since 2005. And even that is not necessarily the worst part. With a hurricane comes a storm surge, a bulge of water driven by winds and lower pressure in the hurricane’s center. This can be several meters high, well above the tidal surge height, and can cause devastation on huge scales.
Irma has already leveled the island of Barbuda, a few hundred kilometers east of Puerto Rico, and just missed Puerto Rico itself. It’s currently headed for Florida, and hurricane watches are in effect from Jupiter on the eastern coast to points south and around the peninsula to just south of Fort Myers. Again, this is all as I write this (Thursday afternoon, Sept. 7), and the situation is changing rapidly. It’s not possible to know exactly where it will hit or how powerful it will be when it does (beyond extremely and perhaps cataclysmically), so if you live in the southeastern U.S. please get up-to-date details. Check the NOAA National Hurricane Center often. Be cautious, and be safe.
But just because we don’t know everything about this hurricane doesn’t mean we know nothing. And one thing we know for sure: Climate change has had a hand in making it the behemoth that it is.
Before I even start, let me be clear: My immediate concern is with the people and places in this storm’s path. I have lived through hurricanes in the past, and my heart dreads what many have already experienced and what others are about to go through. But there are also people and groups out there who are using this hurricane to continue their long game of attacking science. That too must be discussed, now, so that you are aware of them going into this situation. These groups never rest, and they most assuredly won’t hesitate to use this catastrophe for their own political purposes. They already have. [UPDATE (Sep. 8, 2017 at 15:00 UTC): And right on schedule, our climate-science-denying pollution-loving head of the EPA Scott Pruitt has chimed in, literally saying now is not the the time to talk about this. Incredible.]
One of the worst offenders, both for the scope of their denial and their ability to actually harm science on a global scale, is the current House Committee on Science, Space, Technology. Ever since the Republicans won the House majority in 2010 they have stacked this committee with science deniers, including (and especially) the chair, Lamar Smith. Their Twitter feed has been used to spread outright anti-science propaganda, and on Wednesday it was true to form:
This is an especially pernicious tweet, because it sounds reasonable, but in fact is another in a long list of dangerous attacks on the integrity of science.
Unsurprisingly to those of us who don’t have our heads in the sand, that tweet is wrong, or at the very least misleading. The Washington Post has an article written by my friend Chris Mooney about this. I strongly urge you to read it, since he goes over this very well.
To be clear: It’s not known why we seem to get pulses of hurricanes in the Atlantic, and then periods of relative quiet. The situation is complicated, of course, because a lot of factors are involved. But to be certain, even in slower years, there are still plenty of hurricanes that form in the Atlantic. It’s just that none has hit the continental U.S. since 2005. It’s possible that there are slow, long-term changes in the Atlantic causing it, but it’s also possible that climate change has been showing its hand as well.
The thing is, the idea that scientists “blame” climate change for hurricanes, specifically Harvey, is luidicrous. That’s not at all what scientists are doing. What they’re saying, firstly, is that hurricanes form because that’s what hurricanes do. In the summer, warm water + rising air + the Coriolis effect makes cyclones, and these can grow.
What scientists are also saying is that climate change affects how hurricanes form and how they behave. This isn’t speculation, it’s inevitable. Hurricanes feed off warm water — it’s literally the source of their energy. If the water is warmer, there’s more energy to be tapped, and waters are definitely warmer now than they used to be. So is air, and warmer air holds more moisture, so there’s more rain. That part is simple.
The next part is not. While climate change can make it easier for a hurricane to grow, it may also affect wind shear that can cut the head off of a growing hurricane, preventing it from forming. So, it’s not clear how our warming planet affects the number of hurricanes in a given season.
What is clear, however, is that climate change makes the most powerful storms even bigger, giving them more energy and increasing their top wind speeds. The signature of this in the Atlantic has already been seen, and a climate science paper published in 2008 lays it out starkly:
Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere.
That’s the very first line of that paper. The authors clearly wanted to state their case right up front.
Not-so-incidentally, one reason Hurricane Harvey was so catastrophic to Texas last week is that it moved so slowly, so it had more time to dump its deluge of rain. Why was it slow? There was (and is) a blocking pattern, a high-pressure system over the mid-west, and this prevented the usual northward movement of a Gulf hurricane. Why was there a blocking pattern? There’s evidence tying these to global warming as well: The warm air means a weaker jet stream, so it meanders in latitude. The jet stream is pretty far south right now, and kept Harvey over Texas (it’s also keeping smoky air over the Midwest from more northern fires as well, as I can see very well when I look out my window in Colorado).
Harvey did vast damage to lives and property. Irma will as well. We don’t know what Jose will do, but it’s a Category 3 hurricane following a few days behind Irma. Climate change is making the damage from these huge storms worse. As we face down these monsters, we must not deny the science.
As climate scientist Peter Gleick put it,
We need to listen to climate scientists now, as we should have been listening to them for decades. There are people out there saying we shouldn’t be politicizing these hurricanes … but they have already been politicized. When the president of the United States denies climate change, when he fills his cabinet with more of his ilk, when he continues to nominate them to important climate-related agency offices, then it is long past time to talk politics and hurricanes.
As I wrote on September 1, when Hurricane Harvey was still pummeling Texas: “Discussing how climate change amplified the effects of Harvey is not politicizing the event. Ignoring/denying those effects is.”
Correction (Sep. 8, 2017 at 15:20 UTC): I originally wrote that 300 kph winds were equivalent to an F3 tornado. That's using the old Fujita scale; however, meteorologists now use the Enhanced Fujita scale, where that wind speed is rated EF4. My thanks to Mark Westbrook for pointing this out.]