Curry's Hallowe'en Piece

Well, I don't think she'll be able to save the Italian Flag stuff. But she does keep a man guessing.

I have read Judith Curry's Hallowe'en post Decision Making Under Uncertainty Part I . The criticism I can offer here, that the Obersteiner and Weitzmann critiques are rather less inclined to catastrophic outcomes and probably biased to the relatively near future, is of a very different sort than my critiques of the Italian flag, or others' critiques of other seemingly baldly elementary errors. And the statement

The net result of such a feedback loop is an overconfident assessment of the importance of greenhouse gases in future climate change.

while slyly implying an overstatement of said importance, is at least relatively unobjectionable in its literal content. We could, after all, be overconfidently underestimating greenhouse gas sensitivity as well. Now I'm reasonably convinced by James and Jules that we have the thing well bracketed, while much of the community thinks the low side is better constrained than the high side. Presumably Curry's audience does not want to hear this sort of thing.

Once she gets off trespassing directly on James' turf without mentioning James (surely a faux pas among climate bloggers) and starts talking about the near term future of modeling, she seems to be channeling me.

If we assume that CO2 sensitivity dominates any conceivable combination of natural (forced and unforced) variability, what do the simulations actually say about 21st century climate? Well, the sensitivity range for the IPCC calculations are essentially in the same range (1.5-4.5C) that was estimated in the 1979 Charney report. And the calculations show that the warming proceeds until about 2060 in a manner that is independent of the emissions scenario.

So exactly what have we learnt about possible 21st century climate from the AR4 relative to the TAR (and even relative to the 1979 Charney report) that refines our ability to set an optimal emissions target? I suspect that we are probably at the point of diminishing returns from learning much more in the next few years (e.g. AR5) from additional simulations by the large climate models of the current structural form.

Yup.

The big new push in the climate modeling enterprise is for Earth Systems Models. These models are beginning to include biogeochemistry (including a carbon cycle) and ecosystem interactions. Some are proposing to incorporate human dimensions, including economics models and energy consumption models. Such models would could in principle generate their own scenarios of CO2, and so reduce the scenario uncertainty that is believed to become significant towards the end of the 21st century.

There is also a push for higher resolution global models to provide regional information, particularly on water resources. There is currently no evidence that global models can provide useful simulations on regional scales, particularly of precipitation.

Another push is for credible predictions on a time scale of decades (out 20 years in advance). This necessitates getting the natural variability correct: both the external forcing, and the decadal scale ocean oscillations. I don’t expect the models to do much of use in this regard in the short term, but a focus on the natural variability component is certainly needed.

So it seems like we are gearing up for much more model development in terms of higher resolution and adding additional complexity. Yes, we will learn more about the climate models and possibly something new about how the climate system works. But it is not clear that any of this will provide useful information for decision makers on a time scale of less than 10 years to support decision making on stabilization targets, beyond the information presented in the AR4.

Yup.

In fact I'd say that 10 years is extremely optimistic given current methodologies.

Further climate modeling has relatively little foreseeable policy relevance. We have done as much as we can in terms of policy advice. It's far better than some claim, and yet limited in what it can reliably achieve in future. We know the scope and scale of the damage we are doing, but we don't know the details, and probably won't until they come to pass. It's one thing to predict a falling vase will shatter, another to predict where the pieces will end up. Policy makers want regional predictions, and the models are not likely converge regionally. After the fact, somebody can always find a study saying "See! Just like we said!" and ignore the contradictory study.

At Curry's conclusion,

The strategy (primarily model based) has provided some increased understanding and a scenario with about 3C sensitivity that is unlikely to budge much with the current modeling framework. A great deal of uncertainty exists, and emissions target policies based on such uncertain model simulations are not robust policies.

she refers to a formal definition of robustness given earlier in the piece as [a property of] "a strategy that formally considers uncertainty, whereby decision makers seek to reduce the range of possible scenarios over which the strategy performs poor".

I don't know as it's fair to suggest that strict emissions targets are not robust in that sense, though. Essentially, one can always squeeze more toothpaste out of the tube; one cannot easily put it back. That being the case, one could argue that the most stringent emissions scenarios that are consistent with economic well-being would be the most robust in this sense.

So, on careful reading, I find several points of emphasis to disagree with, which seem to be preparing to lay the groundwork for a somewhat skewed risk assessment. We'll see. To my surprise, I also find an extensive section with which I am entirely in agreement.

The main point, though, is that it is hard to imagine that this was written by the same person who has made so many elementary errors in the recent past. What we see here is a tolerable amount of counterspin, surely no worse than some of the spin out there by other mainstream scientists.

If Dr. Curry proceeds at this level of cogency, maybe she can start a meaningful conversation after all. I'd advise her to let the dreadfully posed flag business drop. I won't pursue it if she doesn't. And I'd advise her to take comparable care in future. This isn't some veiled threat, it's simply an assertion that people are on the lookout for elementary errors now, and that Curry will be called out on them.

This piece is, mysteriously, far less disappointing than several recent ones. While there are points with which I disagree it doesn't seem remotely as amateurish as recent ones have. I genuinely hope it represents the sort of thing we can expect in future.