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[UPDATE (Nov. 12, 2013 at 20:30 UTC): The conclusion I draw below — that the signature of global warming is too weak to see in current cyclone development — is not correct. It turns out a 2008 paper shows that the strongest cyclones have an increased maximum wind speed over the past few decades due to warming waters. The issue is important enough and detailed enough that I decided it warrants its own article, so I wrote an update to all this. You can read what's here first, but then please go read the followup. We're seeing the effects of global warming now.]
Yesterday, the supertyphoon Haiyan made landfall in Vietnam and China. Reports are still coming in, but many are confirmed dead and there are certainly many more injured. There’s considerable damage to property, infrastructure, and so on. Luckily — if that word is even appropriate here — the storm had weakened considerably before hitting those countries.
It was at its full and fearsome strength when it came across the Philippines last week, and the devastation there is almost beyond imaging. There are certainly thousands dead, with some estimates as high as 10,000. Over a half million people have been displaced, and millions more affected in one way or another. Humanitarian aid is pouring in, a bright spot in this dark moment.
In situations like this, it’s common to ask why these things can happen, how these things can happen, and even to call them “an act of God.”
Feeding the Monster
However, we know what causes large-scale cyclones like hurricanes and typhoons: heat. Specifically, warm water, which provides energy to the storm. The water warms the air above it, which responds by rising. Surrounding cooler air is drawn in, is warmed by the water, rises, and the cycle continues. As it grows, the rotation of the Earth sets the huge air mass spinning, and you get a hurricane (or, as they are called when they’re in the Pacific Ocean, a typhoon — the generic term is a tropical cyclone). It continues to strengthen as long as more energy is available.
Perhaps you see where this is going. The more warm water there is, the more energy the tropical cyclone can get. This is why we see them in the summer, not winter; the water must be warm. And if the water is warmer than usual, or there’s more of it, the system can grow until it becomes a monster.
But we know — we know — the oceans are warming. A huge amount of energy is being stuffed into them, because we know — we know — that excess carbon dioxide in the air is preventing the Earth from being able to radiate away some of the energy that comes down in the form of sunlight. The process is as simple as it is terrible and damning: More CO2 means more energy, which means more heat stored in the oceans.
And that means either more strong hurricanes and typhoons, or stronger ones overall.
I’ll note, with some care, that we cannot say that any specific storm is due to global warming. As climatologist Michael Mann says, it’s like throwing loaded dice; you might have gotten two sixes naturally in any given throw, but over time they’ll turn up more than they should randomly.
The ocean waters in the Pacific have been warming in recent years. Haiyan fed off that, and there have been a greater number of intense storms recently as well. Haiyan had sustained winds of 195 miles per hour and gusts up to 235 mph just before it made landfall; speeds usually thought of for tornadoes, not hurricanes. It is one of if not the strongest storm ever to make landfall in recorded history.
Can we say that global warming directly made Haiyan the monster it was? No, of course not: There are many, many factors that can affect the size and strength of a storm. The exact path, the upper level winds, the moisture content of the air: These all contribute to the strength of a cyclone.
Can we say then that global warming contributed to the typhoon’s strength? Even that can be a little murky. It’s very difficult to disentangle the various factors that cause a cyclone to form and grow. It’s worth noting, for example, that the Pacific’s vast reservoir of extra warm water fueled the typhoon across its path. However, the current Atlantic hurricane season has been fairly weak, due not to lack of warm water, but instead most likely to plumes of dry air and more than usual amounts of wind shear, which tend to choke off hurricanes before they can form. This is why the recent IPCC report has “low confidence” that global warming contributes significantly to current cyclone activity*. It’s not that global warming doesn’t contribute, it’s just that we don’t know.
But all this is talking about the current conditions, the cyclones occurring now. What about the future?
The Warming Future
While it may be difficult to see the effects of global warming on cyclones today, that almost certainly won’t always be the case.
We know that climate change is real, and that the planet is warming. We also know that the oceans are warming, and that they feed cyclones. Things may fluctuate over a single cyclone season, or even over a timescale of years. But over decades, these conditions will make themselves known.
As time goes on, and the overall heat of our planet increases, the likelihood of more and more powerful storms increases as well. At the very least, as oceans warm up, there’s a lot more fuel for them.
At Climate Central there’s an interesting article about where this all may lead; some researchers are saying there will be fewer but more powerful cyclones, others say they will be both more powerful and more frequent.
That’s my concern. We may not start seeing Haiyan being the new normal for some time, but by the time that happens, it’ll probably be too late. You can’t start worrying about paying for your retirement when you’re 64; if you do, you’re screwed. You need to worry about it decades in advance.
Global warming is like an evil 401(k). Ignore it, and you’ll be sorry eventually.
I think we’re getting plenty of warning of what the future will be like. Global warming is very real, and very real right now. We have the science to back up the claims. We know temperatures are on the rise. We know sea levels are going up, polar ice is melting, glaciers are retreating, and a whole passel of other problems. And we know these effects are due to human influence.
Supertyphoon Haiyan may or may not be one of them. But it’s certainly a harbinger of things to come. At what point will we stop calling them an act of God, and instead an act of man?
* Note that “low confidence” is not the same as “unlikely”; it just means they can’t be confident one way or another. This is yet another reason I’m not overly thrilled with the IPCC reporting style; it’s easy to obfuscate their actual meaning.