It would depend. The AGW theory simply states that there is a greenhouse effect which can be increased or decreased by humans. It doesn’t say that there’s no other factors in the universe that could possibly effect the global climate. There most certainly are other things factoring into the climate and changing any of those will most certainly change where things are. That doesn’t disprove the greenhouse effect since you’re not modifying anything that has to do with greenhouse gases.
If you can show that our understanding of the physical nature of the molecules and elements making up the greenhouse layer are different than we currently understand them to be, -that- would certainly be a thunker.
Hi Blake – I’m a little surprised to see claims of unfalsifiability directed at AGW. How is it different from theories of tornado formation or oceanic circulation?
**1. First falsifiable test of AGW:**
Can the human-produced carbon dioxide (and other gases) retain extra heat in the atmosphere?
The answer to this question is clearly yes, but it could have been no. If the asymmetric stretch absorption CO[sub]2[/sub] were in the range 2-3 μm instead of around 4 μm and 13-15 μm, it would not be a greenhouse gas (the Earth emits thermal IR in the range 6-30 μm or so) and AGW would have been falsified.
It is a result that meets your criteria:
It is replicable
It would lead to AGW being rejected
Actually, I don’t know enough about chemistry to know if it is subject to a statistical test. I suspect your #3 requirement is inappropriate for the wavelengths of IR that CO[sub]2[/sub] absorbs. Could you elaborate on whether you accept these measurements despite the fact that they are not a statistical test? I would guess that the error values for the measurements would suffice, wouldn’t you?
But as you mention, it’s not really enough that we know that. We need more information…
2. Second falsifiable test of AGW
Are the burning of fossil fuels and other human activities the source of the additional GHGs in the atmosphere?
Luckily, we can trace our own input of carbon due to the fact that fossil fuels have a slightly different isotope ratio of [sup]12[/sup]C to [sup]13[/sup]C than modern carbon found in the atmosphere. We can trace the isotope ratios of carbon in ocean and atmosphere, and discover that the additional signal of anthropogenic carbon is detectable:
Citation: Quay et al. 2003. Changes in the [sup]13[/sup]C/[sup]12[/sup]C of dissolved organic carbon in the ocean as a tracer of anthropogenic CO[sub]2[/sub] uptake. Global Biogeochemical Cycles Vol. 17, No. 1.
(N.B. ∂[sup]13[/sup]C is negative in these measurements because fossil fuels have more [sup]12[/sup]C than [sup]13[/sup]C. Plants preferentially take up [sup]12[/sup]C over the heavier isotopes of C.)
It would lead to AGW being rejected if the anthropogenic carbon were found to not remain in the atmosphere.
Again, I don’t think the one statistical test notion applies here. Would you accept the confidence interval of the carbon measurements instead?
There are some people who would say that this is really all you need to know – no one disputes that humans burn large amounts of fossil fuels, that the combustion products go into the atmosphere, and that works to retain heat.
But to really give AGW another falsifiable test, why don’t we test it against other theories of what could change the temperature of the globe on average? 3. Third falsification test of AGW
This one’s a little different from the others, in that it’s actually not a falsification of AGW – rather a falsification of an alternative hypothesis, that solar irradiance changes explain the changes in temperature.
How do we know the sun’s not just heating up the Earth more? Fortunately, we can measure TSI, Total Solar Irradiance, and find out if that has changed.
Citation: Foukal et al. 2006. Variations in solar luminosity and their effect on the Earth’s climate. Nature v. 443, pgs. 161-166.
It is replicable
It would lead to AGW being rejected if TSI were found to be large enough to account for the observed changes in temperature.
Again, I’m not sure the “single statistical test” idea applies here – what test would you perform? 4. Fourth falsification test of AGW
Again, a falsification of an alternative hypothesis, that volcanic action explains the changes in temperature.
It would lead to AGW being rejected if volcanic emissions of GHGs were large enough to account for the observed changes in temperature.
Again, I’m not sure the “single statistical test” idea applies here – what test would you perform? But wevets, tests #3 and #4 are not tests of AGW, they just test alternate hypotheses! You can’t declare AGW correct just because an alternate fails!
True, but if you eliminate the alternate hypotheses, the un-eliminated plausible hypothesis becomes increasingly attractive (implausible hypotheses remain unattractive.) Deduction is not a frequent pillar of Popperian philosophies of science, but that does not make it less effective a tool of logic. There may be some undiscovered factor that could be tested against AGW, and that’s fine. But we don’t put everything on hold until all the undiscovered things are discovered, because that will literally never happen. 5. Fifth falsification test of AGW
Is the amount of anthropogenic GHGs sufficient to account for the observed warming?
It would lead to AGW being rejected if GHGs were insufficient to account for the observed changes in temperature or would cause much larger changes in temperature than observed.
This one actually is amenable to statistical tests – those are elaborated on in the linked paper.
I think part of the problem here is that I would disagree with your definition of AGW, Blake. I would define AGW theory as stating: Human emissions of greenhouse gases have the potential to increase the Earth’s average temperature and change the general state of Earth’s climate.
This appears to differ from your definition of AGW, since you’ve alluded to specific predictions or models of how much temperature would rise as AGW.
I completely reject the notion that future models are a test of the falsifiability of AGW (note that I have used models calculated about the past as a falsifiability test in the ballpark sense.) I also completely reject the notion that models are AGW. Models are built taking into account the principle of AGW (that human emissions of GHGs can change the Earth’s temperature and therefore its climate.) In the same way that this is not the Theory of Gravity, but uses the principles of the Theory of Gravity, models are not AGW, but use the principles of AGW to make predictions.
Of course I read it. The problem is the final link. We know that humans are emitting gasses that are GHGs. We know that the Earth has been warming. We know that the amount of CO2 in the atmosphere has increased - either from one vanishingly small amount to another, or by a large percentage, depending upon how you look at it. We don’t know that these GHG emissions are actually causing the warming we’ve seen. It certainly seems reasonable, but no one has yet demonstrated that human GHG emissions are causing the warming we’ve been experiencing.
The greenhouse effect, as I understand it has been fairly conclusively proven. Comparing the Earth to the Moon or Mars and other planets has allowed us to calculate that without an atmosphere and greenhouse layer, the Earth would be roughly -0.4F.
We know that there is a greenhouse effect and what it’s overall contribution is. The question is what gases produce how much of the effect and how much effect modifying those values will cause.
Now since we know the process by which the greenhouse effect works–heat is collected within the material and then radiated back out in all directions, rather than just back out into space–it’s principally a question of how much a particular gas at a particular concentration absorbs heat and what the limit of absorption is. That can be done in a laboratory.
Since we can measure the concentration of gases in the atmosphere, we can use the above-collected data and math/computer simulation to determine what will happen by changing the concentrations of the gases. To verify that these values are correct, what we do is we take all of our measurements of the atmosphere over the course of the last X number of years (the longer the better) and make those changes in concentrations in our simulator and see if the output temperature is the same as that seen in the real world.
Of course, since the output sun is non-constant, you need to add that in. Since the ocean is a big heat sink, you need to add that in, since …so on and so forth, your simulation needs to also include quite a bit of other stuff to match the real world output, but solving for those is pretty much the same process. You do your best lab testing to determine the physical properties, plug that into the simulator, and see if what you get matches the real world.
Now we’ve got a good dozen simulators and their output is getting better as more things are added (like solar output and oceanic bodies and so forth), but this is all being tested against our recorded past.
With something with that many variables, getting anything which basically resembles the real world output is actually quite impressive. If you can accomplish that, it’s really quite a bit of a proof. But at the same time, that means that it’s quite easily possible that some of your percentages are wrong and it all just happened to come to the right answer. BUT, that’s why there isn’t just one group doing lab tests, there isn’t just one group creating climate models, there isn’t just one group measuring real world states, etc. Where one group might get a couple figures transposed or measurements wrong, if all all 12 independent and competitive groups are coming up with very similar results and those results match back to real world data, I’d tend to buy that–noise in the data aside–we’ve got a legitimate test on our hands.
What’s the goal here? I mean, this discussion is enlightening and interesting, but I can’t help asking what the purpose of it all is. Is anthropogenic global warming falsifiable - does it really matter? Regardless of whether human activity causes global warming, shouldn’t we be taking all steps to minimize our output of known greenhouse gases anyway, just in case? Or is the goal of finding AGW falsifiable merely in order to continue irresponsible practices without care for the cost?
Don’t we have a duty to do our part to take as much care of our environment as we can, even though the Earth can shake us off like a bad cold when looked at in geologic terms? If we continue to dump billions and billions of tons of greenhouse gases into the atmosphere and it turns out that AGW is correct, what then? Too bad so sad? Sounds wildly irresponsible to me.
Going back to the asteroid analogy posted earlier, shouldn’t we be doing all we can to minimize our chances of getting hit by the big one instead of just saying, “ah, screw it?” If we do all we can and it’s AGW isn’t true, we’ve lost nothing (and hopefully the world’s better for it.) If we do nothing and AGW is true…well.
IMHO yes, if you take away those last three words.
We do not know if they are irresponsible.
Yes. How best to do it is a very difficult question.
We don’t know if GW is beneficial or not. It might just be staving off the next ice age. We don’t know what the long-term effects of sea level rises will be. Sure, certain areas will become submerged, but will other areas become fertile? How will it affect the weather? We simply don’t know. More research is needed.
We know too little and determining the falsifiability of AGW will help considerably.
I am vastly skeptical of computer models. I don’t believe that any of them have been shown to be accurate. They require extensive tweaking to match past data. The Earth is not sufficiently understood. Plus there’s the issue of the researchers wanting to find something of interest.
Which is the reason why there’s a certain probability of reliability given to the output and margins of error. And I’d question the veracity of your statement that everything has to be “massively tweaked” to reach something like earthly results. You can look at the PDF I linked to and you’ll see that while there is variation between various people’s attempts to recreate the conditions and separate them into parts, overall everything rises and falls quite nicely with one another.
It should also be noted that there is no simulation made by anyone–simplistic or decently complex–which says that increasing the partcular gases which make up the greenhouse layer will do anything other than increase the average global temperature. While the preciseness of models might be an issue, short of proving that the whole concept of a “greenhouse effect” is false, there is going to be global warming on some scale or another.
Do you mean no simulation published? Unfortunately, this falls into the ‘Well, they would show warming, wouldn’t they?’ field and back to the OP’s issue of falsifiability. And given what happenned to Lomborg and others, who’s going to dare publish one anyway? Note that I think that that last is very sad.
I mean that no one yet has been able to create a climate model based on our physical understanding of chemistry and whatnot that produces any other result. to the best of our knowledge, exact numbers aside, more greenhouse gases means an increase in global temperature.
“To the best of our knowledge” is certainly not a guarantee, but no honest climate scientist says otherwise. They say that for any one particular climate model that it’s got X% chance of being correct and Y% chance of being totally flaming wrong. But X is a larger number and has been steadily growing over the last 60 years, while as Y has been steadily shrinking.
X isn’t 100% so you’re perfectly free to place a bet otherwise, but the smart money is on the people who have the understanding of the physical chemistry and whatnot.
Lomborg was tried for and “convicted” of falsifying data and discarding negative results. What exactly is bad about that?
He’s taken to court and the court decides against him. He appeals and the second court decides in his favor. I see that happen every day in cities all around the world. If this is a grave injustice to fight court battles, sometimes winning, sometimes losing, I’m not seeing it.
What exactly is your recommendation over having peer reviews and trials? What great flaw in the justice system is so grievous that we must replace the whole thing?
I think a little basic chemistry will help you there. Given the massive numbers of molecules involved, if human-generated GHGs can absorb infrared in the ranges I mention in the earlier post, they will absorb in that range.
It is magical thinking to believe that somehow the GHGs are there, they’re human-emitted, but they aren’t retaining heat the way laboratory measurements indicate that they are.
Theories are not enough. We need experimental evidence. Nobody has shown that human GHGs are actually significantly absorbing IR. And nobody has shown that if they are, the absorption is actually producing the warming we are seeing. If things were as simple as you suggest then falsifiability should be fairly simple. But it isn’t. Earth’s climate is monstrously complex, and a lot more research is required.