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