Is Anthropogenic Global Warming Falsifiable?

Not sure whether to put this here or in GQ, but I figure it’ll end up here anyway, so I’ll phrase it as debate.

So, for background I’ll refer you to Popper’s essay on falsifiability. Basically the Popperian standad of science is “the criterion of the scientific status of a theory is its falsifiability, or refutability, or testability.” IOW a theory is only scientific if “the theory is incompatible with certain possible results of observation” Or to put it another way the theory should predict something, and if that prediction fails then the theory is considered wrong. A theory that doesn’t do this isn’t science.

Now there are many other non-Popperian definitions/standards of science. But the Popperian definition is the most widely accepted. It is also the one with the greatest utility when trying to separate psuedoscience such as Astrology form real science, and this is why it is invariably the definition used in the various court cases concerning Intelligent Design. So I’m not looking for debate on the Popperian definition itself. For the purposes of this debate I’m accepting that the Popperian definition is useful and accurate.

So, what possible results of observation are incompatible with the theory of AGW?

Not the fact that the temperature is increasing in line with CO2 emmisions.

The increase in temprature is the very observation that AGW theory was created to explain. For the purposes of this discussion I want to accept as axiomatic that small-c climate change is occurring. Temperatures are rising, they have been rising steadily since since C1860 and more erratically since C1600.

Not the link to CO2 levels. Atmospheric CO2 levels have been rising in a nearly perfect exponential fashion since C1600 and show little to no evidence of recent increases. Moreover historicallly CO2 increases followed temperature increases, just as they have in the present warming event. Cause can’t follow effect. this isn’t to say that CO2 doesn’t cause warming, but the mechanism by which CO2 levels increased started in 1600, well before the invention of the internal steam engine so if a lack of correlation falsifies AGW then it has already been falsified. Now if someone had predicted that temperatures would continue to rise paralleling CO2 increases that would be acceptable of course. But the models don’t; do that. they all work on complex interactions. that’s not a bad thing in itself, but it does mean that the mere fact that CO2 levels increase roughly inline with temperature isn’t a falsifiable prediction because if they don’t the hypothesis isn’t rejected. For example, for the last 11 years temperatures haven’t risen at all despite record atmospheric levels of CO2.

What is being debated is the theory that the rises are anthropogenic. The IPCC notes that all the rises up to 1950 were just as likely to be natural as anthropogenic. So I am working here with a null hypothesis that human activities have made no detectable difference to global temperature. IOW that temperatures had been rising up to 1950 as a result of natural factors and have continued to rise as a result of natural factors.

Now I understand this is a complex field and relationships aren’t simple. But the question isn’t why predictions can’t be made. The question is whether predictions have been made. It’s not science if the theory isn’t incompatible with certain possible results of observation.
In previous threads people have suggested that Hansen’s 1988 models qualify as falsifiable predictions. The problem I have with them is that they predict everything. They cover such a wide range of scenarios. If the temperature trend had continued unchanged then model scenario B would have predicted it. And if temperature had increased scenario A would have predicted it. And if temperatures had levelled off then scenario C would have predicted it. IOW the model predicted any plausible outcome that might have occurred if global temperature changes were purely natural. To paraphrase Popper “I could not think of any climate behavior which could not be interpreted in terms this model”. And as Popper notes this is not scientific. A theory that predicts everything predicts nothing. Hansens models are not incompatible with any possible results of observation that we might get if climate change is entirely natural.

Lest you think I don’t understand how complex this is, I’ll let you in on a bit of my autobiography. I’m an ecologist/plant physiologist. I’ve been employed as a scientist to study climate change, and I’ve been published on the subject in Global Change Biology, the premier journal in my field. I’ve collected data and constructed models. I understand that it’s difficult. But I also know that I have never needed to engage a hypothesis that wasn’t falsifiable. Even though most of my work has been conducted in natural ecosystems where control is impossible I know that you can always construct falsifiable hypotheses if you are engaging in good science.
So I ask those of you who accept AGW and who believe it is good science: what evidence could I show you that would lead you to reject AGW? Obviously a prolonged period of cooling despite an ioncrase in atmospheric CO2 levels won’t do it. In the last 10 years global temperatures have been stable, and for the past five years the temperature trend has actually been negative fig 1. We’ve already had recent papers stating that temperature may not increase over the next decade, but nobody is predicting that they must decrease. IOW this isn’t itself a falsifiable prediction. In fact this makes me even more skeptical of AGW as a theory. It really does predict everything, since it can be used to predict prolonged periods of global cooling as well as periods of global warming.

To pre-empt questions of what evidence I would accept that would lead me to accept AGW. I’ll accept it when someone can show me a peer reviewed paper that 1) Provides replicable evidence for its conclusions 2) Presents a prediction that will lead to AGW being rejected. 3) Analyses observations and concludes, based on a previously acknowledged statistical test, that there is a >95% chance that human activities have produced a measurable effect on global climate. Not a 95% estimate but an actual 95% probability. That’s the evidence that I require to accept everything else as science. AGW isn’t allowed a lowered standard.

To pre-empt comparisons with evolution and other similarly complex topics that have been proved by a body of evidence, I’ll point out that Darwin gave a falsification 100 years ago: if any structure can be shown to exos that couldn’t; derive form previous structures. To which I will add that if anyone can show me a bird fossil in pre-Cambrian sediments or show me that dog DNA is less similar to human DNA than to jellyfish DNA I’ll also consider it falsified. It isn’t any harder to produce falsifiable predictions for theories built on a body of evidence. It’s usually much easier.

So the GQ and the spark for debate is: what evidence could I show you that would lead you to reject AGW? One again I’d like to stress that the question isn’t why falsifiable predictions can’t be made. The question is whether falsifiable predictions have been made. According to Popper it’s not science if the theory isn’t incompatible with certain possible results of observation. So what possible results of observation could I show you that would be incompatible with AGW?

Any evidence for any theory which more accurately recreates the historical climate and conditions of things in modern times, would do. That happens to be the standard for all theories.

The only challengers to the greenhouse gas based climate change theory that I’ve seen are that the sun is hotter/cyclical or that scientists/the UN is falsifying data. The former really doesn’t seem to be based on anything but a couple of very short term graphs that have been mangled, and the latter requires a conspiracy of greater size than has ever been seen on the planet since the Illuminati.

I’m no scientist, but I would assume if you could show that the level of greenhouse gasses in the past had no effect on temperature that would falsify it. Right?

We even had a discussion before on the stunt that “Lord” Monckton made regarding the link on “fig 1” (Yes, I was surprised that you want to pass that as good science.)

It ain’t good.


The alternative theory is that it is all natural. And the evidence is “These results suggest that 20th Century warming trends are plausibly a continuation of past climate patterns. Results are not precise enough to solve the attribution problem by partitioning warming into natural versus human-induced components. However, anywhere from a major portion to all of the warming of the 20th Century could plausibly result from natural causes according to these results.”
Loehle, C. 2004; “Climate change: detection and attribution of trends from long-term geologic data.

And the IPCC itself says that pre-20th century events are plausibly natural and uninfluenced by humans.

So since you now have evidence of an alternative theory that that as accurately recreates the historical climate and conditions of things in modern times, do you reject Global Warming?
Of course you don’t.

Can I ask if you actually read the essay? Because your response is a classic example of what Popper said you can not do in science. It is easy to obtain confirmations, or verifications, for nearly every theory — if we look for confirmations. Confirmations count only if they are the result of risky predictions. The fact that AGW recreates historical climate and conditions of things in modern times doesn’t make it science. All you’ve done is gone and looked for confirmations that theory is true.

In fact your answer is non-responsive handwaving. What evidence could I show you that would constitute evidence for a theory which more accurately recreates the historical climate and conditions of things in modern times? It’s turtles all the way down. What is the actual evidence that I could collect? Not vague references to evidence, but actual observations that I can go out and collect?

In short, what is the falsifiable prediction that you believe AGW makes? Surely it isn’t “It explains things at leats as well as the alternatives”?

No, it certainly is not. The standard, as already noted, is falsifiability. Freudian psychology and Astrology are not considered science because they are better than any alternatives.

The major challenger is the one that I out forward in the OP: that it is all natural and the precise drivers are too complex to understand.
There are any number of non-scientific theories that are more accurately explain events than a null hypothesis of “it’s natural”. No theory more accurately represents the origins of birds and their diversity in modern times than “God did it”? Evolutionary theory doesn’t come close to being as accurate as “God did it” because “God did it” represents everything perfectly 100% of the time. No matter what evidence you find “God did it” explains it 100%.

Does this mean that you accept “God did it” as a scientific? Of course you don’t. That’s because science isn’t based on accuracy. If you had bothered to read Popper’s essay you would know why. It’s because “God did it” and AGW are accurate because they can be used to explain everything. “I could not think of any behavior which could not be interpreted in terms of the theory. It was precisely this fact—that they always fitted, that they were always confirmed—which in the eyes of their admirers constituted the strongest argument in favor of these theories. It began to dawn on me that this apparent strength was in fact their weakness.” AGW suffers from the same weakness. To admirers like you this constitutes the strongest argument in favor of the theories. But it is the every antithesis of Popperian science.

So no, sorry “It explains everything better than the alternatives” does not constitute evidence that I can collect.
But please, if you can think of any actual evidence that I can collect then post it.

Possibly, but what is the observation you are proposing? What data can I go out and collect that will show you that the level of greenhouse gasses in the past had no effect on temperature? Everyone agrees that in the past temperatures rose and then CO2 levels increased. Would that evidence convince you that greenhouse gasses in the past had no effect on temperature? I can show you plenty of times in the past when CO2 level increased and temperature declined. Would that evidence convince you?

This is the question: what evidence can I collect that would lead you to reject AGW?

I can easily provide examples of evidence that you could collect that would cause me to reject evolution, or the germ theory of disease or megafauna overkill any other scientific theory that I accept. So what evidence could I collect that would cause you to reject AGW?

:confused: Nothing in those links suggest the figure is inaccurate in any way.
So are you saying that the figure is inaccurate and that temperature in the past 6 years hasn’t fallen. If not then what “stunt” of any relevance are you referring to? If so then how do you explain almost identical figures in this paper?

And would you care to address the actual subject of the debate: what evidence could show you that would cause you to reject AGW?

I don’t have much time, but recently one component of AGW, the Water Vapor Feedback was confirmed. What is important here is that many people against AGW told us that that was not happening.

The scientists at RealClimate have something to say regarding the overall falsifiability issue:

The conclusions are still wrong. Even the Nature paper reports that:

IMHO I do remember that the temperature graphs that include the recent century show periods of almost 20 years were there was very little change, the problem is that AGW makes the temperature jump up after those periods of stability.

BTW there are issues with that “Energy and Environment” publication:

I disagree with your premise. Popper’s definition is a workable one for experimental sciences but discounts all observational sciences which include commonly accepted scientific disciplines such as cosmology, geography, astrophysics and paleontology. Going by the strict standard posited in your OP, none of these would be counted as science.

If I argue that “frog extinction in the lower San Juan Valley was caused by an increase in pollutants caused by plastic manufacturers”, this is strictly not a falsifiable statement because I have no other San Juan Valleys, no other frog ecosystems and no other universes without plastic manufacturers. I can build up models and make inferences from smaller scale experiments but it’s never going to be possible for me to generate a falsifiable experiment unless I can build replica universes.

Observational sciences lean heavily on modeling and statistics and come from a different philosophical tradition from experimental sciences. Given that you work as an ecologist, I’m puzzled as to why you believe falsifiability is a good criteria for AGW when it’s clearly not the working definition of observational science.

Well, if we continue to produce climate gases and temperatures fail to rise, global warming will be falsified. Conversely, if we significantly reduce emissions, yet temperatures rise unabatedly over a period long enough to exclude possible lag/inertia issues, anthropogenic global warming will be falsified. Unfortunately, we don’t have the means necessary to set up a rigorous control experiment (and if we had, the issue would be pretty much void, anyway), and models can only go so far, but the in principle falsifiability is there.

Conversely, the hypothesis that it’s some unknown natural process is unfalsifiable pretty much by definition.

Quite. The OP indulges in a spot of equivocation between logical falsifiability and practical falsifiability. Any half-decent AGW statement should be logically falsifiable; the problem is that obtaining the data that would falsify it is near impossible, simply because we’ve only got one Earth, and we’re all sat on it, screwing with the data. Assuming, perhaps unfairly, that the OP would like at some stage to exclaim, “aha! Your theories are unfalsifiable, and should therefore be discounted,” it should be noted that the argument applies to every theory of climate change, be it anthropogenic, solar cyclic or intergalactic nazi lizard-based. Assuming we’re not going to throw up our hands and give up all hope of ever understanding our global climate, this standard isn’t a helpful one in determining a theory’s worth.

Should any passing deity be kind enough to provide us with a control Earth, of course, then things will be different.

Did you miss where I said that i didn;t want to debate Popperian science?

And did you miss where I said that I am an observational scientist: an ecologist.

And did you miss where Popper used an example from astrophysics (gravitational lensing) to defend GR as being good science

Let me assure you that Popperian science works perfectly in ecology, geography and astrophysics at least.

But that’s OK. You’ve admitted that AGW isn’t falisfiable by definition. Next thread we can debate whether it’s science at all.

And I repeat Popper: it is easy to obtain confirmations, or verifications, for nearly every theory — if we look for confirmations. This apparent strength was in fact their weakness

But I never referenced the conclusions. I referenced a single, accurate figure.

So can you please stop hijacking my thread.

So would you consider that the decline in temperature in the middle of the last century to falsification? Temperatures declined despite increased production of “climate gases”?

Thank you. The first actual evidence. But as you point out, we don’t actually have any method of collecting such evidence.

Of course it is. It’s actually an admission of ignorance. which has always been a sound scientific defence. A scientist isn’t obliged to accept the existence of gods just because she can’t come up with a better theory to explain a phenomenon. She can say that gods themselves are untestable and hence unscientific and ascribe it to natural effects.

It would be a strange world if we had to accept something as science simply because we couldn’t come up with a better explanation. No?

Fine, you admit that AGW doesn’t meet the standard Popperian definition of science. Not only that, but it can not meet it.

Assuming that you are right (which I don’t think I do) then using Poppers standard this just means that any study of climate change is not a science.

Why isn’t it helpful? Why can’t I evaluate a theory as scientifically worthless if it fails to meet the criteria of scientific worth? This seems like a total non sequitur. How else should one evaluate a theory’s scientific worth beyond gauging it against criteria of scientific worth?

If I told you that I was studying the geology of Pluto using a crystal ball, would you accept my study as scientific simply because we have no way to scientifically study the geology of Venus? Or would yo declare it to be unscientific because it doesn’t meet your criteria of scientific worth.

Your statement here seem like a non sequitur, but please feel free to expand on your reasoning. I would genuinely like to know how the fact that a scientific study of climate change is technolgically impossible makes it harder to determine a theory’s scientific worth. I would have thought it made it easier.

I have yet to see one decent test of the falsifiability of AGW. Part of the problem is that we really don’t sufficiently understand what’s going on. Perhaps a bigger part of the problem is the terrible treatment of those who depart from the consensus. Bjorn Lomborg is the classic case, though ironically, he thinks AGW is true, just disagrees on what we should do about it.

Why put the Lord in quotes? He’s a Viscount and as far as I can tell his title is legitimate.

I disagree on two of your examples, both cosmology and astrophysics make theorectical predictions that can potentially be falsified by either observation or experiment e.g. cosmic background radiation (WMAP), gravitational wave amplitude from the early universe (LISA).

I suspect that a geologist and/or paleontologist will be along shortly to refute the other two as well.

I’m not equipped to make that judgement; however, I can promise you, in 50 years from now, if we’ve continued to blow out greenhouse gasses and the temperatures have stayed at the level they are now, I’ll happily grant that AGW has been falsified – and I do mean ‘happily’, because me being wrong about this appears to be by far the most favourable alternative when compared to the potential disasters that are thought to come bundled with a global rise in temperature.

Well, we could try to reduce emissions, and see if temperatures rise anyway…

But AGW isn’t untestable like gods are: again, if there is no rise in temperature, there is no global warming, and hence, no anthropogenic global warming. And even the existence of gods (or the supernatural in general) would have to be taken into consideration if it turns out to be impossible to find another explanation.

But what you actually are proposing is to accept having no explanation in favour of an explanation you don’t like; if that’s a way to do science, it’s a way that’s new to me. Any possible explanation (gods aren’t, as far as science is concerned, a possible explanation; AGW certainly is) is automatically favoured over none at all; only if that explanation has been ruled out can one revert to a state of ignorance.

The thing about AGW is that it’s such an eminently reasonable assumption to make: CO[sub]2[/sub] does have the simple physical property of being what’s called a ‘greenhouse gas’, i.e. it is able to absorb and emit radiation in the thermal infrared range, and we have elevated its concentration in the atmosphere; that this leads to warming is the natural conclusion to draw, and what looked like warming was the reason to look for such a mechanism in the first place. Of course, there may be some as yet unknown (to me, at least) ‘heat dumping’-mechanism, but to posit such in the absence of evidence for it would be highly unscientific. (That, by the way, in the past carbon dioxide emissions lagged behind temperature rises is a consequence of there not being a natural mechanism to throw the CO[sub]2[/sub] emission/immission equilibrium out of balance – dinosaurs had preciously little industry, in other words.)

Perhaps a bit of a hijack, but what would that actually change? If we now ruled that, yes, AGW is fundamentally unfalsifiable and hence to be expelled from the realms of good science, that doesn’t rule out the possibility that our continued emission of greenhouse gases leads to catastrophic warming in the slightest; we just wouldn’t be allowed to call it ‘science’ any more when we’re discussing this possibility. It would merely be a difference of label, not one of content, and otherwise the discussion would have to go on pretty much the same way it does now: we should hope that AGW is false, while worrying about (and planning for) the possibility that it is true.