Monday, May 12, 2008

Are you avin a laff?

Round and round the mulberry bush...

Roger Pielke, 30 April:

there is in fact nothing that can be observed in the climate system that would be inconsistent with climate model predictions. If global cooling over the next few decades is consistent with model predictions, then so too is pretty much anything and everything under the sun.
Me (in the comments):
over the 30 year time frame there will be strong warming
Roger:

I see that you neglected to address my central question

Me:
I explicitly wrote "over the 30 year time frame there will be strong warming" - and actually 20y would be a safe bet too.

Roger:

I see that you have once again avoided addressing this question.

Me here in more detail:
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.

I could do a detailed calculation about the probability of different trends over the next 30 years, but that's already been done.

Roger:

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.
Me:
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.


Roger:

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.


Me:

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).

Roger again (not in response to me, but bringing up the topic again on his blog):


You can just clear all of this up by answering my original question:

What observations of the climate system to 2020 would be inconsistent (lets say at the 95% level of certainty) with the climate model projections of the IPCC AR4? It is a simple question. use global average surface temps from UKMET as the variable of interest if you'd like, since that is what we've been discussing, or use a different one.


Me, hopefully for the last time:
Stott and Kettleborough estimate that the global mean temperature in the decade 2020–30 will be 0.3–1.3 K greater than in 1990–2000 (5–95% likelihood range)
and
Knutti et al. find that the projected distribution of likely surface warming is independent of the choice of emission scenario for the next several decades; that the probable warming for 2020–30 relative to 1990–2000 is about 0.5–1.1 K (5–95% likelihood range)
(these being direct quotes from the paper I linked to earlier).

As I mentioned back then, I think these forecasts do have some limitations, but since I pointed them out to Roger 10 days ago it is more than a little tendentious of him to repeatedly insist that they do not exist, and furthermore to pretend that he's been met with nothing but dodging and evasion in response to his question about which observations over the next few decades would be inconsistent (at the 5% level) with the model forecasts. The reason why that paper specifically looked at decadal averages over a 30 year interval is because on this time frame the GW signal is clearly visible above natural variability, but its magnitude is not very sensitive to emissions scenarios (within reason). But it is a simple matter of reading off the graphs for anyone who wants a different forecast interval. However, it seems quite clear that Roger is more interested in pretending that the answer has not been provided, than in actually looking at it. He's avin a laff.

Also relevant: Eli Rabett and RC.

33 comments:

Mark said...

I've only scanned the relevant comment threads on Prometheus, but I wonder if the problem is that Roger just can't see that something like this

"Stott and Kettleborough estimate that the global mean temperature in the decade 2020–30 will be 0.3–1.3 K greater than in 1990–2000 (5–95% likelihood range)"

is an answer to his question. Perhaps you have to complete the last step for him.

James Annan said...

I really have no idea what is going on in Roger's head. He has just posted up a graph (based on the RC one) which shows that the model ensemble for 2000-2007 comfortably includes all observational analyses over that interval, and still concludes

"one could properly claim that the surface temperature observations 2001-present fail to demonstrate consistency with the models of IPCC AR4 at the 95% level."

It's just mind-bogglingly wrong. I have commented over there (if his blog will allow it).

EliRabett said...

The point about the global response being pretty much independent of the emission scenario over a few decades (and within limits of the climate sensitivity) is an old one that Hansen made in his 1988 paper.

Hank Roberts said...

Wow.

He's completely inverted how the confidence range in statistics work, hasn't he?

95 percent overlap or no good at all?

Roger said...

Hank-

Consider the question:

What are the chances that the distribution of observations match the distribution of model realizations?

Are you seriously suggesting that you'd be happy with a 5% probability?

Check your Allen Murphy on forecast verification for a somewhat different view.

Hank Roberts said...

Roger, you've misunderstood me again.

"We are used to the spaghetti graph, but the AR4 has a nice way of showing the overlaps between the various studies ...."

http://rabett.blogspot.com/2007/05/it-writes-itself-ethon-after-sharing.html
http://lh5.google.com/image/EliRabett/RjvmGmt8vyE/AAAAAAAAAKU/H0gN5qFcRw4/UntitledAlbum38.jpg

Hank Roberts said...

Or, for that matter

http://upload.wikimedia.org/wikipedia/en/a/a2/Climate_Change_Attribution.png

Yes, look, some of the black line is outside the 95 percent gray.

These folks are just learning to shoot their bow and arrows, and their target looks like a pincushion, arrows all over the place and even some into the broad side of the barn behind the target.

You expect every arrow to be in the center spot?

Watch. They're getting more accurate over time.

Don Thieme said...

Since Roger is talking quantification, someone should probably break this down to the details of the spatial measuring grid, daily weather data, monthly and annual means, etc....

It may be possible to resolve a "trend" over eight years at one station or in a small region. For global climate, though, decadal predictions are going to have such large uncertainties that noone is going to test a model against just one. The "Real Climate" folks seem like they felt this would be understood by readers, but not all their readers actually know how we derive climate from weather measurements.

P.S. I just noticed that the "Real Climate" folks already said this several weeks back.

Tom C said...

It seems to me that we taxpayers have forked over untold millions for climate models with millions of lines that essentially predict an upward march of temperature (smoothed over decadal scales) as a function of CO2 increase, but don't predict anything else except maybe periodic cooling from an eruption. So couldn't the whole thing be simplified to read T = f(CO2)? And, what use are the things if that's is the exent of the preditive capability?

Mark said...

Tom

The 3D atmosphere-ocean climate models predict a great deal more than a steady upward march of global temperature. They predict changes in atmospheric & ocean circulation patterns, changes in rainfall, regional changes in temperature, changes in stratospheric temperature. Some of these predictions can be verified (and some already have been) some cannot (or not yet). Some of these predictions could have been made with simpler models and some could not. That's the way it is with complex models.

Roger has shown what those familiar with the models already knew: that 8-year trends provide a very weak test of the models. He seems to find this surprising and significant. I find his surprise surprising.

James Annan said...

Tom,

What Mark said.

Also, they don't just predict "upward march" but they also quantify it (~0.2C/decade for the foreseeable future). They also predict finer details like more rainfall in total (but spatially heterogeneous), more warming over land and high latitudes...

In a nutshell, what the models tell us is that if we keep on pumping out CO2 in ever increasing quantities, then the warming will continue, and this will almost certainly bring other changes even though we cannot currently quantify these changes accurately on a regional scale.

As for what use they are...well that depends on whether we care about climate change on the 30 year and longer time scale. If we don't, then I suppose we might as well not bother doing any of this research. But even in that case, it would be hard to argue that it is actually less useful than lots of other scientific research like astronomy and high energy physics.

The models do tell us that the changes will not be devastating over that time scale (although they are already noticeable and will only become more so), which must be worth something, even to a denialist.

Michael Tobis said...

Tom's question is based on a common misunderstanding of what the field is and does. I am not entirely happy with Mark's and James' answers. They are true as far as they go, but they leave a very crucial misunderstanding unanswered.

The implication is that we would stop modeling if, say, atmospheric composition stabilized.

The models are a crucial instrument for a science that would exist whether or not there was a policy question. Indeed I sometimes wonder whether both the science and the models would not be further along were it not for all the public attention.

Focusing only on the prognostic uses of these models, however important, contributes to common misperceptions about the field.

Tom C said...

Thanks for the three thoughtful replies. But let me state the question in a different way. Were we to go back in time, would any of these models predict the entry into, or the exit out of, the LIA? I presume that this climate event would not be considered "internal variability" or "noise" or "weather". If the models would not have picked it up, they are fatally flawed and are no more than T = f(CO2) machines.

Regarding the other climatic aspects of rainfall, etc., I would think it fair at this point to have assembled a substantial "scorecard" to evaluate the maturity of the models. What Koutsoyiannis has done, rightly or wrongly, should be only a fraction of what should have been out there for public consumption long ago.

Steve Bloom said...

Tom, FYI your assumptions about the models with regard to the LIA are incorrect. If you can cite Koutsoyiannis, you can look this stuff up.

Re the scorecoard issue, I would commend you to the AR4. While we're on the subject, here's a nice confirmed model result that should be getting a lot more attention (and arguably has not because denialists have nothing to say about it).

Tom C said...

Steve Bloom

You wrote:

"...your assumptions about the models with regard to the LIA are incorrect. If you can cite Koutsoyiannis, you can look this stuff up."

I'm sorry but I don't know what it is that I am supposed to look up. Which assumptions are incorrect? That there was an LIA? Did that get thrown out along with the MWP?

Regarding the paper you linked to, as far as I can tell the models failed spectacularly. That they failed in the same direction as recent warming does not provide any vindication.

Steve Bloom said...

It's one of many such "failures," Tom. It's odd that climate scientists consider such things successes, don't you think?

This is a bit like ignoring all those trapped children in China because earthquake damage models predicted that only half as many schools would collapse. IMHO you should be paying more attention to the fact of the phenomenon itself, and that the important thing the models are telling us is that the trend will continue. Is it not obvious to you that shifting climate zones and storm tracks driven by a warming atmosphere are just a bit of a problem?

Re the LIA/MWP, read the AR4 chapter on paleoclimate.

The assumption I was referring to is that you would blame the models for a failure to accurately model something like the LIA when the problem is actually uncertainty about the forcings and the parameters of the event itself. IIRC the models are perfectly capable of replicating the LIA (insofar as it can be described via proxy records and the very limited measurements that were taken at the time).

Hank Roberts said...

Sanity check please, on the second image I asked about:

http://upload.wikimedia.org/wikipedia/en/a/a2/Climate_Change_Attribution.png

The black line is the observation, the gray area is the confidence range for the model, and some observations fall outside the gray area.

Does it seem like that's the kind of gap Roger's talking about?

Munin said...

Apologies for the nonsequitor, but I was just flicking through a compilation of questions and answers from the New Scientist Last Word column when I noticed a response from Hank Roberts of Berkeley to a question about runny noses.

Hank, was that you?

James Annan said...

Hank,

Roger has repeatedly refused to say clearly what he is talking about, and indeed now admits that he doesn't actually know what he is talking about, so reverse-engineering what might be going on in his head is a bit of a lost cause IMO.

Tom, regarding LIA: given the current state of climate science, if we had known back then that solar output was going to go down, we'd have been able to predict the cooling pretty well. I don't know how well we could have predicted the solar output though. Analogously today, if we know how much CO2 we will produce over the next century, we can predict the temperature change pretty well. Of course the amount of CO2 produced is (to some extent) a matter of choice, and predicting it is socio-economic issue. We have it easy in some respects though: the current radiation imbalance, and near-term committed emissions in the world economy, are large enough that we can e pretty confident over 30 years at least (as I said, 0.2C/decade, plus or minus a bit).

AdamW said...

"Roger has repeatedly refused to say clearly what he is talking about,"

I used to think he just isn't very good at communicating what he means (actually, I still think that).

However, I've recently come to the conclusion that he doesn't actually understand, in at least some cases.

There are some posts of his though, where "not understanding" is possibly a charitable interpretation.

BTW I see that someone's already using his post as "proof" that climate scientists don't know what they're doing. See the comments at Stoat.

Tilo Reber said...

"over the 30 year time frame there will be strong warming"

"Also, they don't just predict "upward march" but they also quantify it (~0.2C/decade for the foreseeable future)."

"Strong" is a handwave on your part. Are you willing to say that there will be .6C warming between 2000 and 2030? Since you believe that .2C per decade is correct, then we should have a 50% chance of .6C or greater by 2030.

50% odds one way or the other seems like a fair bet to me.

So here is my bet to you, James. If a linear regression trend line that is run through monthly HadCrut3 data from 2000 to 2030 shows .6C or more of warming I will pay you 10,000 dollars. If the trend line shows less than .6C of warming, then you will pay me 10,000 dollars.

Now that is pretty cut and dried. Do you believe in the models or don't you? Do we have a bet?

Tilo Reber said...

Just update to April. No warming for the last ten years!

http://tinyurl.com/4de3v7

Hank Roberts said...

http://julesandjames.blogspot.com/2008/04/has-global-warming-stopped.html

Trends

Tilo Reber said...

Hank: "Trends"

Don't care. It's plain as the nose on your face. I gave you the plotted data. No warming for 10 years. Don't believe me, reproduce it for yourself.

Hank Roberts said...

> Don't care

Your faith is unarguable.

Tilo Reber said...

Hey James, are you going to take my bet?

James Annan said...

I don't find the idea of betting $10,000 on a coin toss to be attractive. I see you've already had this explained out to you on Deltoid.

Tilo Reber said...

Do you find standing behind your own work in some meaningful way attractive?

James Annan said...

It's not my work.

Will you bet $10,000 on a coin toss? I don't think many rational people would (due to their nonlinear utility function - you can look this stuff up you know).

Yeah, I know there are compulsive gamblers who bet even when the odds are stacked against them. I'm an intelligent gambler who only bets (large sums) when I judge the odds to be in my favour.

HTH HAND

Tilo Reber said...

"It's not my work."

You certainly seem to be working very hard to defend it.

But okay. In terms of the temperature trend of .2C per decade, if you don't stand behind that number, then what number do you stand behind. What number do you think represents a trend such that we will have a 50% chance of having a warmer trend and a 50% chance of having a cooler trend.

Tilo Reber said...

"Will you bet $10,000 on a coin toss?"

It's not a coin toss in my mind, because it's not the gain or loss of money that is the primary objective. For me it is to see if Climate Scientists will ultimately stand behind their predictions with something other than the public's money. For a climate scientist it should be a wonderful opportunity to show that they are in fact sincere about their numbers.

James Annan said...

I think about 0.2C/decade is a reasonably fair prediction, although I'm currently engaged in calculating my own estimate. I still don't find betting a significant sum of money on a 50-50 proposition attractive.

Tilo Reber said...

Well, let me know what your estimate is and then we can find out how much faith you have in it by what it takes to make a bet on it "attractive".