Thursday, January 31, 2008

Bob Carter on Climate Change (Part III)

[Read Part I and Part II first!]

Carter begins part 3 of his lecture with his second "torpedo": Richard Lindzen's Solar Iris hypothesis. In what has to be the most infuriating part of the lecture so far, he claims that Lindzen's hypothesis has been verified by the fact that cirrus clouds dissipate after a rainfall event, entailing that rain allows more heat to escape into the atmosphere. But as far as I can tell, the argument about the Solar Iris effect isn't about that. It's about whether or not higher ocean temperatures would encourage more efficient precipitation and changes in cloud characteristics. The whole point of Lindzen's hypothesis is to suggest that global warming will be mitigated by a negative feedback caused by changes in rain patterns and cloud cover. That is, as the oceans get warmer, they'll evaporate more, which will cause more efficient precipitation and changes in cloud characteristics which will allow more heat to escape into space, thereby reducing warming. Demonstrating that precipitation affects clouds doesn't prove anything of any relevance. Carter would need to show that increases in ocean temperatures have the sort of effect Lindzen discusses, and he doesn't do that. So "torpedo" two misses its target as well.

Torpedo 3 is much more to the point. Carter rightly points out that concern about climate change is largely drawn from anticipated positive feedbacks thought to occur in the event of warming. On its own, an increased atmospheric concentration of CO2 wouldn't produce the kinds of problematic changes in global temperature that are generating concern among scientists. To be clear, there would be other consequences (like acidification of rain and the oceans, as well as increased capacity for plant growth in water limited areas and better growing characteristics in other places), but the concern about temperature is largely based on predictions of positive feedbacks. Carter gives the example of water vapor, but other positive feedbacks have been described. For example, as temperatures rise, glaciers and ice sheets would be projected to retreat. Because ice is white, while soil, rock and ocean are dark, retreating ice increases the absorption of light by the Earth's surface, resulting in warming.

But it's certainly possible that Carter is right, and on the balance the Earth system is dominated by negative feedbacks. If that were the case, then perhaps concern over climate change is overblown. But the current stance taken by the IPCC is that we have no reason to believe that Carter is right about this, and it's actually quite likely that we've underestimated the positive feedbacks, and climate sensitivity is actually greater than we currently give it credit for being. So for people who say that the science is settled and we can all go home, this point should serve as a wakeup call. But that's not to say that the mainstream view is not aware of it. In fact, the study of feedbacks is one of the most important parts of climate research today, and we're learning more about how they work all the time. So while Carter is right to say that this is an area of uncertainty, it's absolutely unfair of him to say that it in any way disproves the mainstream view. In fact, it's central to the mainstream view, and explains the caution with which the IPCC makes its predictions.

Carter, however, cites a prediction by Stephen E. Schwartz that pegs climate sensitivity at 1 degree for a doubling of CO2. I'm not familiar with the exact paper that he refers to, but I've read some stuff by Schwartz, and I know that he's both controversial and intelligent. So I won't discard Schwartz' opinion as nonsense, because I respect him tremendously, but I also would caution against taking his views as proof of anything.

And I would strongly disagree with Carter's claim that this "torpedo" is devastating to the mainstream assessment. The mainstream view is the result of a comprehensive examination of the available opinions in the field. Taking the conclusions offered by one paper as proof that the mainstream view is wrong is just irresponsible. This is especially clear when Schwartz' prediction actually falls within the confidence interval of the IPCC prediction! So it's not even like the IPCC is saying that Schwartz' prediction is wrong! It's simply saying that most scientists disagree, and for good reasons, but it's certainly possible that Schwartz is right. The strongest thing Schwartz could say in objection is that his confidence interval extends significantly below that of the IPCC, and so some low levels of sensitivity he thinks are reasonably likely are held to be highly unlikely by the IPCC. But if I had to, I could undoubtedly find you a whole collection of reputable scientists predicting at the high end of the interval, upset about the conservative predictions being made by the mainstream community. So to use Schwartz' paper as a "torpedo" is just patently absurd, and I'd suspect that Schwartz might agree (though he'd probably attack the mainstream opinion for other reasons, some of which I likely touched on in this post).

Carter then goes on to lambaste some climate modelers for not being able to properly model the climate. He doesn't actually go into the reasons that modeling might fail, but in the aforementioned post, I briefly sketched some of those kinds of problems, and I happen to think that attacking climate models is a potentially fruitful avenue of attack on mainstream concern. I do think, though, that Carter was out of line in the degree to which he ridiculed these modelers. It's not fair to make them the whipping boys for the problems with modeling. And it's also not fair to suggest that models in general can't be relied on because this one attempt at a climate model didn't produce very good results. Maybe the paper wasn't accepted because of its model; maybe it was worth publishing for some other reason. I've seen model reconstructions, and while they aren't all the best, they're certainly not as awful as he makes them out to be.

In the middle of his tirade, Carter slips in the suggestion that the sun is actually to blame for climate change, which is much more controversial than it looks on the graph he uses. Actually, the solar influence on the climate system has been widely studied, and the IPCC has made an attempt to quantify it. Of course, it's possible that the IPCC doesn't have a good handle on all of the effects of the sun on the Earth system (as has been suggested by people like Willie Soon, Sally Baliunas, Henrik Svensmark, and many others). But while I'm not sure I'm convinced that the solar hypothesis has been disproved, I do think that a lot of work needs to be done if it's going to withstand some of the more convincing criticism it's received.

We'll see if Carter leans on this point in the next part, but hopefully he doesn't, since it's not really the most fruitful line of attack.

[Go on to Part IV]


t3xasfrank said...

On models... In fact, pretty much the whole AGW edifice is based on models (Ch9 of AR4 says so, in so many words, there not being a spare earth to experiment with). The problem is, AIUI, they don't reflect what's happened. AR4 has a nice graphic showing more warming at the tropopause than at the surface as the fingerprint of AGW, but experimental evidence doesn't back it up, does it?

Danny Shahar said...

Well I'm admittedly not a climate scientist, and may well mishandle any answer I attempt to give. So be warned!

Anyway, I'm not exactly sure what graph you're referring to. The discussion of observations relating to atmospheric temperature changes can be found on pages 265-271 of chapter 3 of the report. Perhaps you could direct me to exactly what you're referring to?

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