The answer depends on the exact question you're asking. Here is my view of the scientific consensus on a range of questions:
1) Did global warming cause Katrina? Or Rita? Or any single storm?
As far as I know, there exists not a single peer-reviewed article that connects global warming with the increased ferocity of any single storm. The commonly used dice analogy provides a good explanation of why the case is so hard to make. Assume the weather is determined by rolling a six-sided die, with a six corresponding to a massive hurricane. Now assume that by adding greenhouse gases to the atmosphere, we've loaded the die to make six come up twice as frequently.
Now, we roll the die once, and it comes up six. Did it come up six because it was loaded? After all, a normal die has a 16% chance of coming up six, so it's absolutely possible that the die would have come up six even without the loading.
So the answer to this question is "maybe, maybe not, we just don't know," and I think it's likely to stay that way.
2) Can we identify a trend in hurricane intensity over the past few decades?
There have been several peer-reviewed publications arguing that the data show a clear increase in hurricane intensity over the past few decades. Kerry Emanuel started the controversy with a paper in Nature (PDF) that came out just before Katrina flattened New Orleans. Then Webster et al. published their paper in Science (PDF) that essentially confirmed the Emanuel results.
Subsequent papers by these investigators make the case that this increase in intensity can be connected to global warming (e.g., here and here, both PDF).
However, there have also been legitimate concerns about the analyses, in particular the quality of the data.
There certainly are scientists out there who consider the evidence totally convincing and have entirely accepted the idea that global warming is leading to more intense hurricanes. And there are those who are wholly unconvinced. My sense is that most scientists think there's a good chance these analyses are right, but would not consider the case a slam-dunk. Science is by nature conservative, and important claims are accepted only when the evidence supporting them is overwhelming. That is not the case yet
So I estimate the answer to this question is somewhere around "probably."
3) Will climate change make future hurricanes more intense?
Most scientists agree that increasing sea-surface temperatures will lead to increased intensity. The real question is how much. In a letter to Nature, Emanuel claims a 2°C increase in sea-surface temperature corresponds to a 10% increase in wind speed, which is quite significant.
There is a general consensus that it's very likely that global warming will lead to more intense hurricanes in the future. The exact amount of the intensity increase, however, is much more uncertain.
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Bart Anderson Posted 4:03 pm
25 Oct 2006
I like the dice analogy as a way of explaining this sort of causality.
The gift of explaining scientific concepts clearly will be increasingly valued in the coming years. I hope you write more for Gristmill!
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Zarkov Posted 6:07 pm
25 Oct 2006
No precautionary policy ?
Just wait and see.. ?
What a wonderful frame of mind, I suppose you don't live near the Gulf.
But even if you live inland, there will be an increase in tornado activity.
It seems china bore a lot of wind activity with its typhoons.
Good Luck.
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Andrew Dessler Posted 12:44 am
26 Oct 2006
Regards
PS: I do, in fact, live near the Gulf.
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jjwfmme Posted 1:18 am
26 Oct 2006
So you can never say climate change caused any severe storms. But doesn't this open the way for some absurdity at some point in the future? Let's say we get to the point where the dice are loaded to the point where only one face of the die means that climate change didn't cause a storm's severity. At what point do we release ourselves from saying "we don't know?" Perhaps not until it's too late for the persuasiveness of our certainty to have any impact on the problem.
I think Gore's movie was on the right track when he gave people an idea of the mechanism that creates the severe storms. He showed Katrina moving over the warm water and talked about how climate change means more frequent, unusually warm water. I think this is the better way to go. We can say something like climate change produces patches of progressively longer-lasting, warmer waters, creating more windows of opportunity for severe storms. Climate change creates more vulnerability for bad storms hitting our coasts. Something like that. Maybe someone can say this clearer than me.
I remember Roger Pielke saying that a bigger problem than CO2-enhanced storms ,is that too many people live on the coasts, and that more people move there every day, and that this creates more risk than climate change does. This may be true, but this doesn't take some things into account:
One-- people who choose to live on the coast bargain that they'll get natural hurricanes, but they might feel differently about human-enhanced hurricanes (and some people in third world countries that live on the coast didn't even produce much of the CO2 that caused the problem).
And Two-- stronger hurricanes are a major data point on the public's radar that we are changing the world. If we're creating stronger hurricanes, we can only guess what other problems we are creating.
So anyway, I don't think hurricanes, or even Katrina should be dismissed as part of the climate change discussion...
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Andrew Dessler Posted 1:42 am
26 Oct 2006
Here's my answer to your question: At what point do we release ourselves from saying "we don't know?"
When we get enough good statistics that show that hurricanes are getting stronger. In your example, if six were loaded to come up 80% of the time on a six-sided die, it would only take a few rolls to determine that. If the loading were slight, then it would take many more rolls. Regardless of the loading, at some point we can look at the data and say that the die has changed.
Even at that point, however, we still wouldn't be able to say with great confidence whether a single roll (storm) was caused by loading the die (global warming).
Regards
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David Roberts Posted 1:55 am
26 Oct 2006
There are also plenty of places where we act to address risks we are unable to exactly quantify. What was the statistical chance that Saddam would develop WMD and hand them off to terrorists? Impossible to say, particularly with the state of our intelligence, but the very same people who deride the notion of counteracting global warming happily signed on for a massive expenditure of resources to head off that faint risk.
It's important to understand our state of knowledge around hurricanes and global warming, but it's also important to note, given how arbitrarily standards of proof and evidence are applied to various kinds of risks, that there must be something else going on here besides pure risk assessment. What that something else is -- what makes people so resistant to the idea of addressing global warming -- is a mystery to me, I confess.
www.grist.org
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bookerly Posted 3:45 am
26 Oct 2006
It's the fear of change. Most people fear and resist change (there are personality types that seek change, but they are in the minority).
Most people change only when they feel they must. They don't have this feeling about global warming yet.
patrick
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jjwfmme Posted 12:16 am
27 Oct 2006
That stark warning was given to Tony Blair and his cabinet yesterday by Sir Nicholas Stern, a former World Bank economist, and is said to have left cabinet ministers chastened by the magnitude of the threat posed by climate change.
http://news.independent.co.uk/environment/article1932727....
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EliRabett Posted 8:49 am
28 Oct 2006
The question about NO is an interesting one because no one can make the argument that its being there was caused by recent building. Thus the damage to NO had nothing to do with the economic boom along the Gulf Coast and that smoke screen vanishes.
Eli Rabett
http://rabett.blogspot.com
Ethon's pet bunny
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