Bishop Hill Overpeck notes the problems with attribution statements
Dec 16, 2014 Climate: Models FiveThirtyEight has an amusing article about the competing explanations for the California drought. A bunch of NOAA scientists have reported that it's all down to natural variability, noting that they are pretty sure of their results:
This is the first study to show that a West Coast dry pattern could be triggered by warmer water anomalies in the tropical western Pacific. Seager said researchers feel “pretty confident” about the association because it shows up in all their models. (One objective of the study was to look for factors that could help predict future droughts.)
This seems to me to be a fairly hilarious example of the fallacy I lampooned in this posting a few months back.
But of course reporting that bad weather is down to natural variability rather than the global warming bogeyman is never a good thing for some prominent people and so we also have all The Disreputables hauled out to criticise Seager et al. But this doesn't mean that what they said was not without interest. Take Jonathan Overpeck for example:
They’re assuming that our climate models capture variation and change perfectly and that you can use these climate models to determine whether what we see is due to human causes or natural variations.
Well I couldn't agree more. All attribution statements about climate change depend on GCMs and an assumption that they capture change perfectly, despite all evidence to the contrary.
So can we now just all agree that the IPCC's statement on attribution - that most of the observed change in climate is down to mankind - is simply unsupportable?
Reader Comments (51)
They’re assuming that our climate models capture variation and change perfectly and that you can use these climate models to determine whether what we see is due to human causes or natural variations. Jonathan Overpeck
What more is there to say...
"Well I couldn't agree more. All attribution statements about climate change depend on GCMs and an assumption that they capture change perfectly, …"
This is simply untrue.
Doug
What next, Jonathan Overpeck saying that the Medieval Warm Period really existed?
Or perhaps they might even admit the temperature "pause" is happening!
But you can be sure it is going to be "worse than we thought"!
Ok Doug let us know which attribution statements are not dependent on models. I'm presuming you won't be saying they are based on gut feeling.
I've heard British scientists will announce this week they've attributed heavy rains to AGW. I've also heard the Met Office is preparing a major announcement with or by the UK government about future climate change in the kingdom, all based on regional climate models, the skills of which are known to nobody.
With all these impressive results around us, maybe one of the esteemed scientists can pop by and explain why we've got it all so wrong. I see Doug is at hand already 8)
I just love that!
I guess fly-by-Doug is saying that that they don't capture change perfectly, but the results are tightly constrained and the uncertainties are small. But just guessing. Whatever, the models are useless.
The IPCC's statement actually referred to the warming since 1950 and went something "we're 95% sure that more than half of the warming since 1950 is anthropogenic". If you think this is unsupportable, then I assume you mean that there is quite a good chance (more than 5% that more than half of the warming could be natural - i.e., non-anthropogenic)? Is that a fair interpretation?
If so, there's an easy calculation one could do. The change in CO2 from 1950 to today is about 310 - 400ppm. The change in temperature is about 0.6K. The change in anthropogenic forcing is therefore about 5.35 ln(400/310) = 1.4 W/m^2. If only half the warming is anthropogenic, then that implies a TCR of (3.7x0.3)/1.4 = 0.8K. If we assume that the system heat uptake rate in the 1950s was small and that it is about 0.5W/m^2 today, then that would imply an ECS of about (3.7x0.3)/(1.4-0.5) = 1.2K (and this may be an over-estimate given that the system heat uptake rate in the 1950s wasn't zero). My calculation may be even more of an over-estimate since the AR5 radiative forcing diagram suggests that the change in anthropogenic forcing since 1950 is closer to 1.7W/m^2 than to 1.4W/m^2.
So, if you want to argue that there is a reasonably good chance that more than 50% of the warming since 1950 was natural, you're essentially arguing that feedbacks to anthropogenic forcings are zero (or negative). Given the greenhouse effect, Milankovitch cycles, and other known warming events, this would seem rather implausible and hence that there is only a small chance (say less than 5%) that more than half the warming since 1950 was not anthropogenic. I'm guessing others here (almost everyone I imagine) disagrees, though.
An additional issue is that if the feeback response to anthropogenic forcings is very small (or negative) what process can cause natural warming? If you look at studies of internal variability (and I think Doug McNeall may be an author on a paper like this) it is essentially the same physical processes that drives warming through internal variability as produces feedbacks to anthropogenic forcings (water vapour and clouds). It seems that you want to have your cake and eat it too. You want to argue that somehow our climate is sensitive to internal variability but not to changes in anthropogenic forcings. Some might argue that this is logically inconsistent.
PLEASE
The models have been validated.
[1] Each model has been tested by comparing its output with that of other models.
[2] They are able to reproduce
the training data used to tune thempast climate (some, at least), therefore their ability to predict future climate has been confirmed.aTTP: What greenhouse effect are we given? Is that the one where greenhouse gases have this remarkable ability to trap heat?
Philip,
I think the answer to your second question is essentially yes (remarkable - like catastrophic - is a judgement). However, are you implying that you dispute the standard explanation for the greenhouse effect?
My God are people saying that the science is not settled?
Next you will be telling me Sooty and Sweep are not real? What is the world coming to!
"The change in anthropogenic forcing is therefore about 5.35 ln(400/310) = 1.4 W/m^2."
The physics of atmosphere is very straightforward in ATTFizzy's world (as in the world of EM, who also takes this formula as the fundamental basis).
Martin,
I don't think I've ever thought it straightforward, but, just out of interest, how does it work in your world?
aTTP - Please no greenhouse gas effect debates. Lindzen already put the net feedback of zero or less here:
http://www-eaps.mit.edu/faculty/lindzen/236-Lindzen-Choi-2011.pdf
And nobody is being logically inconsistent. The mere fact that there is an 18 year plateau tells us that natural variation is more dominant than was previously supposed. Trenberth and others had of course previously poo-pooed the skeptics who said that positive PDO might have caused the 1975-1998 jump yet now the negative PDO forms part of his theory of why the pause happened. If you accept that as plausible then you must also accept that skeptics were proven right to be skeptical in the past and you'd be wise to listen more carefully to us now. We also know there was indeed a medieval warm period despite certain scientists trying to deny it. That being the case nobody has a good explanation for why the MWP nor for the subsequent little ice age, nor for any of the warming and especially the cooling events of the past. Whatever caused these events may easily have caused this current mild warming of 0.6K/century. You know this to be true!
To go further, the pause also suggests that there is no real basis for suspecting CO2 is even a driver of climate in the first place. The error bars in the assumptions and the numbers allow many interpretations. Assuming that what cannot be explained must be manmade is like the drunk man looking for his keys under the lamppost because that's all he can see. Whatever that is called, it isn't science!
My own skepticism stems from the memory that a new ice age and forest devastation from acid rain were also supposed to arise from fossil fuels. Both were ridiculously over-hyped. If we go further and point to the deforestation that has actually been over-ridden by reforestation due to warming and/or CO2 fertilisation (according to satellite data) and to the falsified population crisis of the 70's then we form a picture of earth scientists who not only seek out only pessimistic positive feedbacks and ignore all other possibilities but seem to have a fixation about the fossil fuels that sustain our current prosperity.
And then there is physics
From the IPCC: "we should recognise that we are dealing with a coupled non-linear chaotic system"
What is it about 'non-linear' and 'chaotic' that makes you use linear projections based on percentages of CO2 in the atmosphere and assumed forcings from that radiative gas?
Ian,
I didn't make a linear projection.
I'll say some of it.
This ever was was the smoking gun of climate science. That the models had "constrained" the Great Satan of carbon dioxide and its myriad streams was always very unlikely.
But what the dogs-that-didn't-bark also ignored was that the above also required that the models must have already constrained all the other satans, and nobody had received any Nobel prizes for it!
Wasn't there that paper that "showed" if you remove CO2 effects you allegedly can't get the observed temperature variation in recent decades? Never mind circular arguments but I think it did demonstrate that the objective was to decide if human influence was different than natural.
Did I just read that right? ATTP showed that if you assume that CO2 caused all of the warming, you can conclude that most of the warming is caused by CO2? Brilliant!
It is just such a shame science doesn't work that way.
Micky
That modeling exercise you refer to, first done by Hadley Centre and available on youtube, is where the IPCC attribution arose from. It contained a crucial assumption that natural variation was in decline, which is falsified by any explanations for the pause/plateau that utilise natural variation (deep ocean cooling, pdo, etc). Hence there was no longer a scientific basis for the attribution statement to re-appear in the AR5 summary and even less basis to increase the confidence of it - which is really no more than a show of hands anyway. The summary for policymakers is a self-proclaimed policy document designed to increase the cost of fossil fuels by taxation or other means. Whether or not this is based on the science that it purports to summarise seems not be too important to scientists - and indeed to journalists and policymakers, none of whom bothered to read AR5 itself.
Real Climate experts have told the world to spend billions on climate science and models. They have to think of their grandchildren's ability to earn money for doing nothing, but scare people.
We must have faith in the science, because without faith, there is no science, or problem to scare people with
...and Then There's Physics; the problem with taking only the warming post-1950 is that the world existed before 1950 as well.
Look at the slope of Global T in the first half of the 20thC. It is the same as the slope in the second half. But the emissions are very different. Thus your back of the envelope calculation is entirely inappropriate. CO2 emissions just don't have that much effect compared with everything else.
The natural variation that caused the warming pre-1950 can’t just be assumed to disappear so as CO2 can take over.
More than that, every climate scientist knows that emissions don’t correlate with Global T. The UNFCCC demands that they look for the evidence that man is affecting the climate. They must have graphed emissions vs Global T – that is what the IPCC is meant to look at.
But they didn’t put it in AR5.
They must know that CO2 is negligible compared with natural variation because otherwise they would publish the graph and discuss it. Instead they look only after 1950 and hoe no-one notices.
If so, there's an easy calculation one could do. The change in CO2 from 1950 to today is about 310 - 400ppm. The change in temperature is about 0.6K. The change in anthropogenic forcing is therefore about 5.35 ln(400/310) = 1.4 W/m^2. If only half the warming is anthropogenic, then that implies a TCR of (3.7x0.3)/1.4 = 0.8K. If we assume that the system heat uptake rate in the 1950s was small and that it is about 0.5W/m^2 today, then that would imply an ECS of about (3.7x0.3)/(1.4-0.5) = 1.2K (and this may be an over-estimate given that the system heat uptake rate in the 1950s wasn't zero). My calculation may be even more of an over-estimate since the AR5 radiative forcing diagram suggests that the change in anthropogenic forcing since 1950 is closer to 1.7W/m^2 than to 1.4W/m^2.
What is it about 'non-linear' and 'chaotic' that makes you use linear projections based on percentages of CO2 in the atmosphere and assumed forcings from that radiative gas?
I didn't make a linear projection.
It looks very linear. Add this percentage CO2 -> leads to this percentage warming via simple 'forcing' calculation.
You are aware that chaotic systems can react differently and non linearly to the same inputs and that a small input at one instant can have more effect, even in a different sense, than a large input at another instant?
You also appear to expect all feedbacks to be similarly linear and act at the same speeds, whereas a thermohaline feedback may be initiated but take centuries to have effect while a solar event can cause some change in minutes and clouds in minutes to days.
Can we be certain, about uncertainties, around the IPCC's high levels of confidence?
It makes climate science seem like astrological guesswork.
"The change in anthropogenic forcing is therefore about 5.35 ln(400/310) = 1.4 W/m^2."
(...)
I don't think I've ever thought it straightforward,...."
Fizzy - anybody who thinks that 'radiative forcing' is a concept that means something in reality (rather than something that can be simulated in computer models) and who also believes that it can be calculated by a precise formula, is truly living in a world where things are straightforward compared with the barely-understood world that the rest of us live in.
Spence,
No, you clearly did not. You could surprise me by reading it again, and actually giving it some thought. On the other hand, if you want to simply respond with snarky comments like "Ooooh, look what he said, what an idiot", that's also fine. I'd expect little else, to be honest.
MCourtney,
Yes, I'm well aware of that. The IPCC attribution statement, however, refers to the warming since 1950. Also, we have much more information about the period since 1950, than the period before this and hence can make stronger statements about the warming since 1950 than we can about the warming prior to 1950.
Martin,
Ahh, I thought it was something that was quite well defined. I'm guessing you think it isn't?
Fizz - You seem to think that "means something in reality" has the same meaning as "is well defined". Or have I misinterpreted what you just said?
Martin,
I'm not sure. What do you mean by "means something in reality"?
No ATTP, I did read what you wrote, and my summary is accurate. Let me give you an example that is a little easier to understand.
Let us consider a much simpler system. Say we have ten bags, each with two balls which are identical except for the colour; one red, and one blue. I take one ball, blindly, from each bag. From the draw, I take 6 red balls and 4 blue balls. From this, I make a claim that I have light receptive fingers, and I can sense the colour of the balls from touch alone. It is not a perfect capability, but I claim I can get the red ball 60% of the time.
Assessing the deterministic evidence at hand, we find that the expected value of someone who could not detect the difference between red and blue balls would be 5 red, 5 blue. The expected value of someone who can get the red ball 60% of the time would be 6 red and 4 blue. So, from the claimed effect, I could argue that the difference between expected values is 100% explained by my claimed effect.
Why is this not science? The answer, of course, is that there is not just a deterministic effect; there is also a random, or stochastic effect, and that must be assessed. And the stochastic effect is not calculable from the deterministic effects alone.
In my example, each draw is an independent Bernoulli random variable, and the combination of ten draws will, from first principles, follow a binomial distribution. The probability of drawing 5 red, 5 blue is around 25%. The probability of drawing 6 reds and 4 blues around 20.5%; the probability of something other than 5 red, 5 blue is approx. 75%, equally split between red more and blue more. Of course, had I drawn blues, I could have claimed I was selecting for blue. So in fact, it is more probable in this case that I do not draw the "expected value". It shows that it is highly likely that my draw of 6 reds could have occurred from mere chance alone.
On this basis, the claim that light sensitive fingers is shown to be without merit, even though the claimed deterministic effect matched the outcome of the draw. Without calculating this stochastic element, our deterministic claims are insufficient.
For climate, the stochastic element is natural variability. You did not assess at all whether natural variability could explain the temperature rise of the last 150 years. This is where is gets difficult. Drawing balls from bags is easy; each event is independent random and this enables us to use a simple, well known distribution (binomial) to assess the result. For climate, this is not the case. Nobody knows what the correct distribution is, or what the dependency between samples is. The models certainly don't tell us, as they bear no resemblance to natural variability at all. That said, we can rule some models out as unrealistic (e.g. random walk); but that still leaves a wide range of possibilities.
We've been here before of course, and as we know from this paper, for many reasonable assumptions we find that the warming we have seen could easily have happened by chance alone. And I doubt the pause in the nine years since that paper was published would mean the results would be any different today.
In summary, the claim that drawing six balls out of ten provides evidence of light-sensing fingers is not scientific because no assessment of the stochastic element was considered, even though the claimed effect explains 100% of the difference between the expected result and actual result. In the same way, the Cohn and Lins paper shows that the claim that the greenhouse effect is 100% of the cause of the warming is also without merit.
In the case of the light sensing fingers, the claim of 60% effectiveness is chosen to make an apparent match - the conclusions are built into the assumptions based on prior knowledge of the results, as I pointed out in my previous comment. Likewise, the greenhouse feedback can be set to match the observations, and also claiming an apparent match. Neither of these are valid scientific claims, nor are they supported by the evidence at hand when stochastic elements are accounted for.
Spence,
No, you clearly did not understand what I wrote and clearly have no interest in trying to understand what I wrote. Having engaged in discussions with you before, though, this is probably about as good as it's going to get.
Yes, we have been here before and it's still complete and utter nonsense!
What do you mean by "means something in reality"?
Gosh - I'd imagined it was a common enough phrase but here goes...
"Means something in reality" means "has meaning in reality". See a dictionary for the meaning of "meaning" if needed.
“Has meaning in reality” means that the meaning we are concerned with applies to something that exists in reality. (So far as I am concerned, “exists in reality” means “exists physically”.)
So the meaning does not apply to something that can only be imagined, or to something abstract, or to something that can be represented on a canvas, in a computer, can be described in words, etc, but cannot exist in reality.
Does that explain it adequately?
Not really. I still fail to see how something that is a well-defined physical concept (such as a radiative forcing) doesn't mean something in reality. As I understand it, it does.
Yes we've been here before, your last attempt was to get gradually more aggressive while not addressing a single point I made. Eventually you retired to your blog, completely misrepresenting my argument and banning Paul Matthews for pointing out some of the obvious errors that you made.
Yes, I remember that well.
I also remember you said that anyone who simply declared another persons argument as "nonsense", without any supporting evidence or claims, as being the sign of someone not to take very seriously. I remember that well also.
I see you have declared my argument as nonsense without providing any reason or supporting evidence, despite my very careful attempts to explain my position in terms even a layman could understand.
You are right, there is no point in continuing, is there?
Fizz -
Would you please copy and paste the definition of radiative forcing...
Spence,
First part probably true, but exacerbated by your obvious tendency to make blanket and absolute statements (without addressing a single point I made).
If I misrepresented your argument, then I apologise as that is never my intent. I'm not sure I did, but have no interest in investigating further.
True, but I tire of explaining why we cannot simply warm by chance. I have no interest in explaining it again and doubt you have any interesting in discovering why it is nonsense. If you think it isn't, that's fine.
Absolutely. I didn't even think there was really any point in starting.
Martin,
Nope, look it up.
Fizz - I know perfectly well what it is.
you are the one who said "I still fail to see how something that is a well-defined physical concept (such as a radiative forcing) doesn't mean something in reality. As I understand it, it does".
I was going to point out where it does not mean something in reality.
Bye.
Martin,
Carry on. I wasn't the one who made a strong claim about the reality of the term "radiative forcing".
Technically, it is not "by chance". It is an unpredictable excursion of attractor that governs climate. And the only way you could possibly know we cannot warm in this way is if you had mapped out the attractor of climate in full.
If you had done that, you would already have a Nobel prize. Since you haven't, and since all of the available evidence from proxies suggests the attractor exhibits fractal dynamics, we can simply dismiss what you claim to "tire of explaining".
Spence,
I didn't enjoy our last discussion and - as you point out - my behaviour wasn't quite what I would normally hope it to be. I don't intend to start another one with you. If you wish to believe that it is simply an unpredictable excursion of the attractor, carry on.
...and Then There's Physics says
So ...and Then There's Physics asserts that we don't even know the temperature of the planet before 1950.
Wrong.
If you said before the satellites in the '70s you may have a case. But to say before 1950 we couldn't read a thermometer but in 1951 we could? Ridiculous. Come back with a justification for that, please.
We do know the temperature in the first half of the 20thC. It rose at the same rate as the second half of the 20thC. This is a real problem for those who still think CO2 is a major driver of global warming as the emissions came after 1950 - not before.
The key point is that this problem is ignored and waved away as "we have much more information about the period since 1950" instead of discussing the issue. Ducking reality is politics - not science.
...and Then There's Physics, are you discarding the surface temperature measurements?
If not, what is the difference between the scientists of the 1020s and 10s over the scientists of the 2000s and 2010s?
It isn't a question of belief. It is a question of objectively applying a consistent set of scientific principles to problems. I'm applying the same set of principles to the climate problem as I do to the balls-in-a-bag problem described above.
Sure, the climate problem is a lot more difficult. I don't have the convenience of independence of trials which I designed into the balls-in-a-bag example. I don't have the convenience of knowing the distribution that I expect from first principles. It is a harder problem to understand. But it isn't intractable.
The principles that I apply here are not unique to me either; many scientists share my views, and many have published in the peer-reviewed literature on the topic, from Kolmogorov in the 1940s, Hurst in the 1950s, Mandelbrot in the 1960s right up to Koutsoyiannis, Cohn etc. in the 2000s and 2010s. The tools these scientists have handed down are more than adequate to provide some understanding of the scaling behaviour of climate.
But if it helps you to pretend none of this work exists, and that it is all down to an esoteric belief of some random blog commenter, knock yourself out.
MCourtney,
No, I don't. Don't be ridiculous.
Spence,
I'm not really the one ignoring swathes of research.
Are you guys still wasting your time arguing with the ignorant idiot with the laughably pompous pseudonym? He gets it all from SkS and Wikipedia and behaves like a demented adolescent!!
ATTP, this isn't about "swathes of research". It's about why your reasoning in this comment is pseudo scientific nonsense. And I don't even need to invoke fractals to show that; my red ball/blue ball example is sufficient.
(In the red ball / blue ball example I was originally going to suggest that the ability to select red was "psychic power". Yep, your reasoning can be used to "prove" psychic powers. Good job most sceptic organisations have a better grasp of probability than you do)
Anyway, if the work by Koutsoyiannis was wrong, then there would be publications explaining the error made. All we hear at the moment is... crickets. In fact, all climate scientists who have looked at the problem (e.g. Hans von Storch, Armin Bunde etc) acknowledge that fractal dynamics ARE present in the climate system. Although at least IPCC AR5 acknowledges this shortfall, and that climate scientists have no idea of the consequences of this fundamental flaw in their methodologies.
I wouldn't waste any time dealing with this aTTP character - see how he describes sceptics on his own blog:-
"there’s certainly no point in discussing science with climate change deniers. "
What an arrogant pathetic little sh*t this aTTP guy is!
Spence,
I have no idea if Koutsoyiannis is wrong. What I do know is that our climate responds to changes in external forcings. Arguing that those have had a minimal effect on our recent warming and that that is primarily some kind of natural fluctuation is probably wrong. You may, of course, disagree and I, obviously, don't really mind either way. You appear to feel that you have a good understanding of the topic and, so, you certainly don't need to discuss anything with me.
RKS,
You're rather making my case for me. You may note that I didn't actually malign any particular individual, I referred to a generic group of people who deny that anthropogenic influences are the main reason for our recent warming. If that isn't you, you shouldn't be offended. If it is, why not simply own it?
Some characteristics of borderline Aspergers...
⚫ average or above-average intelligence
⚫ difficulties with high-level language skills such as verbal reasoning, problem solving, making inferences and predictions
⚫ difficulties in empathising with others
⚫ problems with understanding another person’s point of view
⚫ difficulties engaging in social routines such as conversations and ‘small talk’
⚫ problems with controlling feelings such as anger, depression and anxiety
⚫ a preference for routines and schedules which can result in stress or anxiety if a routine is disrupted
⚫ specialised fields of interest or hobbies.