Friday, May 02, 2008

"What observations would be inconsistent with climate model predictions?"

Roger Pielke keeps on posting the same question, and keeps on ignoring the replies, so rather than just posting it again in his comments I'll write it out in full here.

First, I should make it clear that I don't accept the true/false dichotomy implicit in his question. Is the Newtonian view of gravity "falsified" by relativity? I suppose so, but in practical terms for everyday applications, it does just fine. Is relativity "falsified" by the Pioneer anomaly? Maybe, at some level. I wouldn't like to bet on that one. No-one is going to "falsify" the fact that CO2 absorbs LW radiation - that doesn't make this statement an act of "faith", it simply makes it true.

That said, some observations would strongly modify our views on the impact of this on the Earth's climate. Most obviously, sustained cooling on the multidecadal time scale would greatly change our estimates. (I'm ignoring the theoretical possibility of major external shocks such as meteors, volcanoes, or nuclear winter). Warming over 30 years is assured, 20 years must be "very likely", 10 years I would certainly say "likely" but that is a bit of a rough estimate. Note that despite the press coverage of the Keenlyside et al work, they don't actually predict any cooling in the future (although they do seem to think it cooled from 1990 to 1998)! Of course there are also upper limits to the expected warming trend (of roughly double the central model projections, at the same level of confidence as I've given the warming/cooling threshold). But I've seen presentations which explicitly draw attention to the possibility of ~5y cooling trends even with a strong background warming, so obviously on the very short time scale we can't expect global mean temperatures to tell us anything conclusive or even highly informative. After all, global temperatures decreased by a whopping 0.22C/year only 10 years ago (1998 to 1999) - that's a rate of 22C per century!! Scary ice age is going to kill us all!!! Not.

I'm sure Roger will find some way of not reading or understanding this. After all, I wrote it in the first comment to his post, and then posted it again in direct answer to his question, and he still ignored it (and according to a comment, Gavin said the same thing previously). I could do a detailed calculation about the probability of different trends over the next 30 years, but that's already been done. FWIW, I think there are some problems with the work described in that article, and intend to have a go myself shortly, but I don't expect to see any really large changes - the issues are similar to those in the climate sensitivity stuff I've talked about before, but I expect the impacts to be smaller in the transient case.

Interesting fact in passing: if the 2008 anomaly is merely +0.3C or greater, then the newest 10y trend 1999-2008 will actually get steeper compared to the current last 10y trend (which is already positive, despite starting in 1998). I predict that were this to occur, some people will start looking hard at 11 or 9 year trends :-) Currently 2008 is running a little colder than 0.3, as Jan and Feb were very cold (but still warmer than the 1961-1990 baseline). But the March anomaly is up above 0.4....

21 comments:

Things said...

I'm sure Roger will find some way of not reading or understanding this.

You don't understand the way Roger's mind works. All you have to do is provide him with several decades and $10 billion in research funding in order to come up with a response and he'll get it immediately.

bigcitylib said...

Roger's version of falsificationalism is extremely naive. And even less naive versions don't track the actual process of science very well. In reality, when presented with apparent counter-evidence, it is often more rational for scientists to add Cēterīs paribus clauses to a successful theory rather than abandoning it.

crandles said...

I can't say I care for the way he is presenting it (ideal for sceptics to use to confirm their prior reached conclusions)

But isn't Roger complaining about the use of statements like 'these observations are consistent with global warming theory'.

Over short time frames the only observations that could be made are either (1) consistent with global warming theory or (2) they are inconsistent with global warming theory but also inconsistent with what we would expect in the absence of global warming theory.

So if such a statement is made about observations over a short time frame then it is meaningless, saying nothing though it gives the appearance of supporting global warming theory.

To me it seems very similar to you riling against statements like we cannot rule out sensitivity of over 7C.

You have been there, done that, done something about it in your IPCC AR4 review comments.

If this is what is behind his post (and this is a big if and others do not seem to be seeing what I see) then perhaps what I would expect to see from you is an attack on the presentation but support of the underlying point with perhaps a hint that you feel you have done more about that sort of thing.

crandles said...

I am wondering if authors include such statements to try to head off any sceptics trying to hijack some part of what they have written and claim the paper falsifies global warming. Roger might be seeing such statments as erroneously claiming support for global warming theory and climate models.

bigcitylib said...

The authors expressed concern that their paper might wind up becoming an Exxon talking point.

Roger said...

James-

Crandles gets it exactly right.

James you do not. You suggest that I somehow expect "to "falsify" the fact that CO2 absorbs LW radiation". Nothing could be further from the truth. I am focused on prediction, not theory. Hence your analogy to Newtonian mechanics vs. relativity is evidence that you continue to talk past my point. So you can claim that I don't "get it" but when you so compeltely fail to get my point, it is clear why you might think so.

James, when you write, "Warming over 30 years is assured, 20 years must be "very likely", 10 years I would certainly say "likely" but that is a bit of a rough estimate" you are much closer to what I am looking for. I am asking for somewhat less "roughness" in these estimates, and grounding them more quantitatively than this sort of hand-waving which is a common response.

And no I am not requiring falsification to be true/false, it is of course probabilistic, as I've written many times.

As far as providing fodder for your skeptic friends, we perhaps disagree on how to best deal with that. I am asking to climate science community to take on this subject openly, and colonize it with clear, rigorous thinking. Ceding the territory to the skeptics (by not giving them "talking points" by staying silent) or attacking people who raise questions (e.g., this post, RC) is exactly the wrong thing to do. Though I am aware that in the climate PR war there are only a few acceptable topics/constructions.

bigcitylib said...

"James you do not. You suggest that I somehow expect "to "falsify" the fact that CO2 absorbs LW radiation". Nothing could be further from the truth. I am focused on prediction, not theory."

The predictions are based on the theory. How is it that the theory should in no way be affected by the fact that it does not appear (in your eyes) to constrain predictions? Now it seems that you are being too kind to the theory. One would surely have to say at this point that the theory is unfalsifiable, no?

Roger said...

BCL-

There are plentiful examples of various degrees of predictive skill based on different methods drawn from the same theory.

For instance, mutual funds are composed based on predictions of future market performance. Any mutual fund manager worth his or her salary will ground their work in a solid understanding of economic theory. The expectation is that such funds will outperform those based on astrology etc. Does the poor performance of a set of funds tell us anything about the validity of economic theory? No.

Weather prediction is very much along the same line.

Theory informs prediction, but falsified predictions from complex models do not invalidate the fact that CO2 absorbs LW radiation. It is good to keep these issues separate, and not to conflate them as James has with this post.

bigcitylib said...

"The expectation is that such funds will outperform those based on astrology etc. Does the poor performance of a set of funds tell us anything about the validity of economic theory? No."

But its reasoning like this that drives many people to the conclusion that economic theory is not really scientific. A lot of math representing nothing. Are you really saying that if for example an astrology based fund did BETTER than one based on solid economic principles, this would say nothing about economic theory?

(If you ever followed day trader mailing lists, you would have seen both varieties of theory doing fine in the late 1990s.)

Tom C said...

James -

While I am not accusing you of this behavior, what bothers me and many others, including Roger, is that we are bombarded with claims from "climate scientists" about: exactly how much rainfall there will be in the SW US in the year 2050, what the temperature of Central Europe will be in 2030, and so on. Moreover, any increase in global temperature is interpreted as a pure response to CO2, with no contribution of internal variability. Then when confronted with the last ten years of data, and a possible continuation of same for many years to come, we are given admonitions of not confusing long term trends vs. noise, and not expecting predictive power from models, etc.

It just doesn't add up. There has to be some sense of discipline in the profession.

Roger said...

"Are you really saying that if for example an astrology based fund did BETTER than one based on solid economic principles, this would say nothing about economic theory?"

Absolutely.

bigcitylib said...

So the economist's motto must be: "True yet useless." "True but unfalsifiable"

And you are claiming that climate science is in a similar state?

By the way I wonder what you would say about the climate models that predicted in advance various climate features of Titan later observed by Cassini? Is it just on Earth that they fail so abjectly?

Things said...

Tom C said: Moreover, any increase in global temperature is interpreted as a pure response to CO2, with no contribution of internal variability.

What? For the IPCC projections some have referenced in regards to this issue, internal variability is intentionally smoothed out and/or not included (e.g. solar in some models). That isn't because internal variability isn't acknowledged, it's because what most people are after in looking at the future projections is the warming trend apart from the noise. Roger likewise seems to make this error when he assumes that the IPCC projections reflect a monotonic warming- they absolutely do not, and in fact even averages of individual models do not (e.g. AR4 Fig 10.5).

Then when confronted with the last ten years of data, and a possible continuation of same for many years to come, we are given admonitions of not confusing long term trends vs. noise, and not expecting predictive power from models, etc.

The admonition is to not judge projections by standards they were not created to address. The AR4 projections are ensembles basically smoothed to remove noise- and when you look at them as what they are- trends for 20 or 30 years (20 in the case of AR4, not sure if it was 20 or 30 for the TAR), studies like this recent Nature one aren't contradicting them.

It just doesn't add up. There has to be some sense of discipline in the profession.

There has to be discipline in judging modeling results on the criteria they were produced under. Smoothed ensemble runs for 20 year periods aren't meant to capture decadal variability. Comparing this Nature study to them without context is comparing apples to oranges.

James Annan said...

Roger,

Getting back on topic: you asked for more quantitative estimates, but did you read the link I provided, where such quantitative estimates were explicitly presented 6 years ago?

If, after reading that (and the two papers it refers to) you still have a question then feel free to follow up.

James Annan said...

Chris and others,

Yes I agree there is a potential problem with people claiming that some convenient observations have too much confirmatory power. I made exactly this point in my recent interview on the "More or Less" program (but I don't think it actually made it to the broadcast). If one is taking a probabilistic viewpoint, then it is not really a case of observations being consistent or inconsistent, but rather weakening or strengthening our confidence in model predictions, and perhaps nudging our best estimate in one direction or another. To take a recent example, if the jetstream had been robustly observed to shift equator-wards then this would have certainly challenged our models, so it seems pretty reasonable to say that the obs (which show a poleward shift) are consistent with what we expect. However I don't think there is an accurate quantification of this effect and the obs are probably noisy so their value, taken in isolation, is not that high.

Accurate quantification is easiest to achieve with global mean temperature, and the simple fact is that the answer - at least, some pretty reasonable answers - have already been provided (eg see that Nature link), but Roger refuses to acknowledge it. Instead he prefers to bluster on his blog about "incoherent, abusive, and misdirected responses". Well you can fool most of the people most of the time, and I guess that is the readership he is after.

Roger said...

James-

If you think that I'm focused on 2020-2030 (the subject of the essay in Nature that you linked to) then you are not really paying attention.

You write, "it is not really a case of observations being consistent or inconsistent, but rather weakening or strengthening our confidence in model predictions" -- I agree with this, and would just note that you take strong issue when I focus on inconsistency, but you are silent about those claiming consistency. But wouldn't your complaint apply to each?

It is of course this double standard offered by modelers that I have highlighted.

Blog bluster, indeed.

James Annan said...

Roger, you started off with "if global cooling over the next few decades..." (my emphasis) which remains on your blog even after several people have pointed out that it is a gross mischaracterisation of the Keenlyside paper. So I pointed you to explicit probabilistic predictions about the next few decades which are as clear as day about the probability of cooling over that time frame.

Now you say you are not focussed on the next few decades...

If you want shorter term, I'm sure you have already seen the Smith et al Science paper, within which 50% of years post 2009 are predicted to beat the 1998 record. But as you can see, this is still a rather young area of science, and Keenlyside disagree to some extent (although not as strongly as some have portrayed it - I think their 10y mean forecast could still validate even if we see some new records).

On the wider point: I don't bother commenting on every minor detail in climate science, but (obviously) I think I have been reasonably fair overall. I've certainly managed to upset people on both extremes of the argument, which suggests I can't be that far wrong :-) (Not that I actually deliberately set out to offend people even if it does come across that way, honest guv.)

EliRabett said...

A warming stratosphere after an increase in greenhouse gases would be a strong refutation of any current climate model.

A refutation of Kirchoff's law would be a strong refutation of any current climate model.

CO2 mixing ratio NOT rising after some other forcing warmed the system would be a strong refutation of any current climate model

The Earth system NOT cooling after aerosol is injected into the upper troposphere/lower stratosphere would be a strong refutation of any current climate model.

Anyone else want to play?

James Annan said...

Global average temperature returning to where it was as recently as 1996 would be a fairly strong refutation....

Low pressure systems turning clockwise in the NH would be hard to reconcile with the models too.

Of course scientists don't usually waste their time stating the bleeding obvious in this way. It is what RC might call the tacit knowledge that anyone working in the area takes for granted.

Note that if the aerosol injection is small enough then natural variability could overwhelm the forced effect over a short interval (and the same goes for some of your other examples). And what about the troposphere warming less rapidly than the surface? But yeah, I get the point. Of course, I wasn't the one who was missing it in the first place.

Zeke said...

Eli:

Would an increasing stratospheric temperature coupled with increasing GHGs really falsify model projections? I was under the impression that CFC-driven ozone loss was at least as significant as GHGs in driving stratospheric cooling, and increasing ozone might in itself produce a slight warming. Though I could well be wrong, so please enlighten me!

EliRabett said...

Zeke, Yes, but not where the actual cooling is observed and not by as much. Follow the links here

James, it pretty much goes back to what big city said in the second post that " Roger's version of falsification is extremely naive", to which I might also add extremely aggressive. Coupled with that annoying whine it gets him a lot of press.