Is Al Gore's Presentation of Global Warming in An Inconvenient Truth Accurate?

[ecofan]

As such, the entire atmosphere is not simply considered as a filter, but is also an emitter.

The author of that statement may be a physicist, but he's seemingly forgotten about conservation of energy. Sure, the CO2 absorbs heat, and then may re-emit it... but in doing so the emitting molecule "cools" again, so there's no net heat gain anywhere. Shuffling it around the atmosphere doesn't increase "global warming" - unless it acts on water vapor and affects cloud formation, which can alter the "greenhouse effect". And, since the direction of re-radiation can be 50% in the "upward" direction, and 50% in the "downward" direction, eventually it's all pretty much going to escape the atmosphere. Of course, any "10 year old" could have told us that, in noticing how quickly the air cools down after sunset.

I guess no "physicist" is immune from blunder, eh?

 

[ecofan]

AIP says that the above paper has exactly 3 citations amongst all peer-reviewed work.

Strange, I could quickly find 21 citations to the work in both papers and books in print.

Do I get a prize for being a better researcher?

 

[ecofan]

Being a second author on a paper is not absolute proof of any real knowledge of the subject matter. A second author could be a person that builds instrumentation, makes samples, writes computational algorithms, etc.

Quite possible, but also possible that the post-docs and grad students are doing most of the work, with the Big Boss writing the final paper and using his clout to get it published.

Order of authorship doesn't indicate who the project director is; sometimes they are alphabetical, sometimes they are random, and sometimes they are ordered by who spent the most time on the task. Take a look at your own co-publications, assuming you have quite a few. How were they ordered as to author? Anyone in this forum ever make it to the Journal of Chemical Physics or the Reviews of Modern Physics? Give us some citations, please...

 

[Gokul43201]

Strange, I could quickly find 21 citations to the work in both papers and books in print.

Do I get a prize for being a better researcher?

Are they all peer reviewed? Books, typically, are not. In any case, the bar for a "landmark paper" is set pretty high. For a comparison, look at the recent list of top cited papers in PRL ( http://prl.aps.org/ ). The papers in the bottom of that page have hundreds of peer-reviewed citations that do show up within the AIP system. Want to guess how many of them get described as "landmark papers"?

 

[ecofan]

I'm not sure I know what "peer review" is anymore. Most of the AGW hacks are now peer-reviewing their own crap, while shutting out the more serious work that exposes them for what they are.

Michael Mann, for example, has become a "peer-reviewer". Will Al Gore be next?

 

[Gokul43201]

Quite possible, but also possible that the post-docs and grad students are doing most of the work, with the Big Boss writing the final paper and using his clout to get it published.

Or, very often, the big boss doesn't even write the paper. But typically, you would have to know your stuff to end up becoming big boss.

Order of authorship doesn't indicate who the project director is; sometimes they are alphabetical, sometimes they are random, and sometimes they are ordered by who spent the most time on the task. Take a look at your own co-publications, assuming you have quite a few. How were they ordered as to author? Anyone in this forum ever make it to the Journal of Chemical Physics or the Reviews of Modern Physics? Give us some citations, please...

In experimental materials/condensed matter physics, it is common that the first author be the grad student/post doc that did most of the work, and the last author be either the PI or a collaborator that provided essential support. That's how we order it in our group, and I know many others that use a similar scheme. JCP does not use alphabetical listing.

Don't you think it is hard to explain how a published author can make such basic errors as we have seen on the site? I would like to believe, for the sake of the Peden on the JCP paper, that the two authors are not the same person.

 

[vanesch]

The author of that statement may be a physicist, but he's seemingly forgotten about conservation of energy. Sure, the CO2 absorbs heat, and then may re-emit it... but in doing so the emitting molecule "cools" again, so there's no net heat gain anywhere. Shuffling it around the atmosphere doesn't increase "global warming" - unless it acts on water vapor and affects cloud formation, which can alter the "greenhouse effect". And, since the direction of re-radiation can be 50% in the "upward" direction, and 50% in the "downward" direction, eventually it's all pretty much going to escape the atmosphere. Of course, any "10 year old" could have told us that, in noticing how quickly the air cools down after sunset.

No, what I was pointing out is that you do not necessarily "keep the wavelengths separated". That is, if only one single line in the spectrum is absorbed by an absorber, but that absorber converts the absorbed energy in general heat, and doesn't simply re-emit at the same frequency, then you get a coupling between the different wavelengths. So the entire layer becomes then an emitter of black body radiation, while only one line was absorbed. But I don't know in how much this plays a role in a typical atmosphere.

 

[ecofan]

OK, makes sense to me. No wonder no one can completely understand the atmosphere... there's a twist at every turn.

 

[vanesch]

Vanesch if I am following your correspondence with the Middlebury author correctly he seems to be advocating a model which equates to an atmosphere 1 molecule thick and so any non-CO2 molecules act as spacers (ignoring any possible absorption by other atmospheric components) an IR photon has only one chance to hit a CO2 molecule and if it misses it's lost to space?

The other extreme is the second viewpoint you reference which suggests the atmosphere is so deep that inevitably all IR photons of the right wave length/frequency will strike a CO2 molecule meaning we are already at saturation point so adding more CO2 is irrelevant?

If this summary is correct how would one go about proving which if any is correct?

In fact, both viewpoints can be correct. In order to understand this, what you need to know is an elementary concept in radiation/matter interaction, which is "interaction cross section".

If you have a beam of particles which transports N particles per second, and this beam hits a slab of material of a thickness d and a density rho (number of interacting molecules/atoms/... per cm^3), then it turns out that the number of reactions per second, M, is given by:

M = A x N x d x rho (at least, as long as M is much smaller than N, which means that the beam is not "depleted" throughout the slab).

In other words, the number of reactions is proportional to the thickness, it is proportional to the density of target molecules, and it is proportional to the number of particles per second in the beam.
A is a constant of proportionality, and if you work out its dimensions, it is a surface.

(indeed, N has no dimension,d is in cm, rho is in 1/cm^3, and M has no dimension).

A characterises the interaction between a particle in the beam, and a target molecule, and is a microscopic quantity that is only dependent on the incident particle and the target (and the collision energy). It can in some cases be calculated from first principles. It is the so-called "interaction cross section" for the specific reaction under study, and is independent of the macroscopic material presentation.

The interaction cross section has the dimension of a surface, so officially m^2, but one usually uses a smaller unit: 1 barn = 10^(-24) cm^2.

For instance, the incident particle can be a photon of this or that wavelength (or energy), the target molecule can be a CO2 molecule, and that's it.
One usually gives the interaction cross section (in barn) as a function of the "incident energy" - or for photons, the photon energy or wavelength. So interaction cross sections are usually plots or tables of the cross section as a function of wavelength.

This function can show "peaks", which means that for certain incident energies (or wavelengths for photons) the value of the cross section increases strongly, to fall back again at a bit higher value. Usually one specifies the center energy/wavelength of that peak, and calls it "an absorption line", but don't forget that it is actually a continuous rising and falling of the cross section.

Note that it is a pretty universal concept. You can have scattering cross sections for neutrons on nucleae, or absorption cross sections for photons on molecules, or fission cross sections for neutrons on uranium nucleae...

It all follows the same universal concept of a 2-particle interaction: you specify the two particles (beam and target) and you specify the kind of interaction (scattering, absorption, another reaction), and you can define a cross section for that.

Now, one can re-shuffle the formula:

M = A x N x (d x rho)

d x rho is the number of target molecules PROJECTED on a perpendicular surface to the beam in the entire slab. So this is the number of molecules one would find per unit of SURFACE if the entire slab were compressed into a thin sheet.

This was part of my argument: the number of interactions doesn't change as long as (d x rho) is the same, so whether or not you have a thick slab (a column) or a compressed sheet doesn't matter. It is also the "difference" between the two views.

Now, we can now calculate A x (d x rho). A was a (tiny) surface, the cross section. (d x rho) was the compressed number of molecules per unit of surface.

So it looks as if we can associate a tiny surface to each of these molecules, of size A, and A x (d x rho) is then the FRACTION of the initial unit surface which is now "covered" with "molecules"... at least, as long as this number is much smaller than 1, so that there is no "overlap". It gives you then "the probability" that a beam particle will "hit" a molecule.

Indeed, if you have N beam particles per second, and each of them has a probability Ax(dxrho) to "get hit", you have N x A x (d x rho) hits per second: our initial formula.

But let us not forget, that's only valid when this probability of hitting is small. If not, you have to "re-adjust" the beam as it depetes throughout the slab - which comes down to saying that the molecules "hide one behind the other" ; it can then be shown that you have:

M = N (1 - exp( - A x d x rho) ), the exponential absorption law, at least under the hypothesis that there is only one kind of interaction: the one under study, and that upon interaction, the beam particle disappears. If scattering happens, the problem becomes way more complicated, but the elementary concepts remain valid for thin slabs.

My main argument was, that in this formula M = A x N x (d x rho), at no point, the ratio of our target molecules (CO2) to any other species appears. It is not because you ADD another, neutral, species to the mixture, that the number of interactions diminishes - which was the principal argument in the first page.

Now, in the second argument, of course, if A x d x rho is a very big number (say, 2000 or so), then the number of interactions M ~ N. Indeed, exp(-2000) is a very small number, negligible in comparison to 1. If now, we double the density of CO2, we would obtain A x d x rho = 4000, and we STILL have M ~ N.

However, things are in reality more complicated. We don't have a monochromatic beam, and there are other interactions. The cross section is a function of the photon energy, in the reference frame of the target molecule. If these molecules move around, then in their reference system, the incoming photon has a bit more or less energy, and hence the cross section is different: this is what one calls "doppler broadening". There are many other small effects. Once you want to take all this into account, you need to write a computer simulation (such as MODTRANS). I would like, myself, to see a more detailed explanation of which effects are dominant, and what does what. It can seriously alter the balance of the radiation.

I've written (small) transport codes myself, in the nuclear domain. I can assure you that the results are sometimes surprising. That said, as long as you take into account all relevant interactions, and if you have accurate enough tables of cross sections (and if you don't make any silly bugs), then there is not much doubt about the result of such a computer calculation: the theory of radiation transport is rather well-understood.

You can compare it a bit to finite-element calculations in mechanical structures.

NOTE:

sometimes one defines cross section in a different (but equivalent) way:

M = A x N x d x rho

Let us consider the geometrical section of the incoming beam to be S (surface), and let us assume that the beam is homogeneous across this section.

Let's multiply by 1: S / S:

M = A x N x d x rho x S / S

Now, d x rho x S is rho x V is the number of target particles in all exposed to the beam.

M = A x (N/S) x (d x rho x S)

N/S is the number of incident particles in the beam per unit of time and per unit of surface: it is the flux density of the beam.

So we have:

M = A x (incoming beam flux density) x (total number of exposed target particles).

 

[vanesch]

BTW, an interesting thing to read about a radiation transport model is given here:
http://forecast.uchicago.edu/archer.ch4.greenhouse_gases.pdf

 

[Andre]

That link says:

The sensitivities of climate models are often compared as the average equilibrium
temperature change from doubling CO2, a diagnostic number that is called ΔT_2x. Most
models have ΔT_2x between 2 and 5 K, which is the same as 2 to 5°C. You can use ΔT_2x to estimate a temperature change resulting from some change in CO2. Note that this is the ultimate temperature change, after hundreds or even thousands of years have passed (see Chapters 7 and 12).

This is the essential point of dispute. If you run the numbers along MODTRAN, the result is around one degree (note they changed default to tropical atmosphere, which gives higher results). The highest I got was some 1.5 degrees (tropical atm) with maintaining relative humidity, which already implies positive feedback. To crank things up some more, even more positive feedback is required. However autocorrelation of individual climate records do not support that positive feedbacks are prevailing over negative feedback.

 

[vanesch]

This is the essential point of dispute. If you run the numbers along MODTRAN3, the result is around one degree (note they changed default to tropical atmosphere, which gives higher results). The highest I got was 1.4 degrees (tropical atm) with maintaining relative humidity, which already implies positive feedback. To crank things up some more, even more positive feedback is required.

The only point of discussion here was not the necessary temperature change and all the feedback that goes with it, but rather the absorption in the atmosphere of black body radiation, and how this changes or not with the CO2 content.
In other words, the radiative forcing. We had two "claimants" which claimed no dependence on CO2 level, for two extremely opposite reasons:
- one claimed that all the CO2 in the atmosphere couldn't absorb in the worst case not more than a millionth of the thermal radiation emitted by the Earth - but I think after a tedious discussion that it starts to be clear that this was based on a gross error (multiplying the spectral fraction absorbed in a thick layer by the ratio of CO2 over N2/O2). So this was pretty clearly wrong.
- another one claimed that the atmosphere was already "totally black" in the CO2 bands, so any change in concentration wouldn't alter anything.

It turns out, if I understand well - correct me if I'm wrong - that this last position is not fundamentally wrong: at the peaks, the CO2 does already capture everything it can. But there seem to be two effects which make that there is still a tiny change in absorption, due to the "wings" of the peak, where the cross section is such that the atmosphere is not totally black yet, and can hence absorb more if the concentration is increased (widening of the peak), and the black body radiation from the atmosphere itself.

Now, when running that model, one then sees that instead of 340 watts per m^2, only, say, 339 watts get out, meaning a radiative forcing of 1 W or so.

Now, it was my understanding that these numbers are about sure. One can tweak them still a bit more or less, but they are not off by a factor of 10. So trying to prove that AGW is bogus simply because the radiative forcing is 0, with a simple physics argument, is not going to work.

The whole dispute is of what is going to be the temperature effect of a given radiative forcing, as I understand well.

At least, that's how I understand it.

 

[ecofan]

I think we're all forgetting that the fellow in question is trying to simplify the situation for the layman, who doesn't know feedback from a family barbeque. While that may be an impossible task, I personally don't think he's that far off in his final result and conclusion, and we all know the general public isn't capable of understanding any of the technical issues.

Incidentally, I have an ( unnamed ) friend who works for an (unnamed ) agency that can find out everything about anyone, and I've asked her ( yes, it's a female senior analyst ) to check out the author in more depth. I'll report back if I learn anything interesting, but it may take a while.

 

[vanesch]

I think we're all forgetting that the fellow in question is trying to simplify the situation for the layman, who doesn't know feedback from a family barbeque. While that may be an impossible task, I personally don't think he's that far off in his final result and conclusion, and we all know the general public isn't capable of understanding any of the technical issues.

But if "simplifying" means "making gross errors" and if the motivation behind it is "well, given that in ANY CASE nobody's going to understand what I'm talking about, so I can just say ANYTHING that sounds good, as long as it can be erroneously be understood as supporting my position", then that's nothing short of trying to manipulate the gullible public.

You see, in "simplifying for the public", you have to be very careful NOT to fall in the above trap of "telling nonsense which sounds good to an idiot in the street". You have to limit yourself to the essential effects, and explain them honestly, eventually by finding analogies and so on, but NEVER by doing something grossly wrong.

Simplifying doesn't mean "doing away with complicated effects", when those effects are ESSENTIAL in the result. Simplifying means: doing away with those effects of which you found out that it doesn't play a significant role in the result.

 

[ecofan]

I'll take some small credit for talking him into removing the complexities to which you so ardently objected. The version running now is very straightforward, is extremely generous to the AGW hysterics in it's analysis, and appears to me to be "good enough for government work". I'd suggest if you can do a better job for the layman, you put fingers to keyboard and do so. Something like this is sorely needed by the general public, who only hear the biased media side of the argument. If you can do a better job, go to it...

 

[vanesch]

I'll take some small credit for talking him into removing the complexities to which you so ardently objected. The version running now is very straightforward, is extremely generous to the AGW hysterics in it's analysis, and appears to me to be "good enough for government work". I'd suggest if you can do a better job for the layman, you put fingers to keyboard and do so. Something like this is sorely needed by the general public, who only hear the biased media side of the argument. If you can do a better job, go to it...

You see, that's the difference between the author of that page and myself: I don't consider myself qualified enough to go and tell the public about it. Now, when I have to think that it took me several messages and that it took other works and other people (like you) to CONVINCE that guy that he was making an elementary and gross ERROR (not a simplification), then I have to say that I think he's not qualified either!

I looked again at his page. It is less wrong. But it is still wrong for two reasons.

We've decided to be exceptionally generous to all concerned in the debate and look at the worst-case scenario, where we'll say that all of the available heat in the CO2 absorption spectrum is actually captured. We know that man is responsible for about 3 % of it, so with the simplest of math, we have .03 x .08 = .0024. And remember that 8% figure was actually larger than reality, since the two side peaks don't have much energy to capture.

What's wrong here ? The 8% and the 3%. The 8% is wrong, because it is 8% of the black body radiation that can get captured by CO2. Now, as that OTHER anti-AGW guy told us (and he's not totally wrong), the CO2 window is "almost entirely black already". But there are OTHER "black windows", mainly due to water vapor. So that part of the BB spectrum can already not get out. So the "8%" is not 8% of what can get out, it is much more, because a large part of the remaining 92% are already blocked. And the 8% is not 8%, because the wings of the distribution get larger. So, the fraction of the ESCAPING BB radiation on which the CO2 has a handle, is much more than 8%. It's closer to something like 15%. (see a MODTRAN calculation when you first put no CO2, and then, say, 0.1 bar of CO2: the difference in absorbed power is of the order of 15%)

The 3% is wrong, because even if the postulated human CO2 contribution NOW is of the order of a few percent, one makes models for a DOUBLING of the CO2 content, so then the postulated human contribution is 100% (we go from 100% to 200%). One treats the case that by the end of the 21th century, man will have doubled the CO2 content of the atmosphere, and it is in THAT case that some people say we might have a problem.

So his upper limit, using the approximations he makes, is rather that CO2 has the potential to alter the BB escaping radiation by something like 15%. But even granting him his 8%, with a doubling of the CO2 content, we would then arrive at an absorption of 8% of the power that would otherwise have escaped.

In reality, that's then a gross OVER estimation of what AGW proponents claim! According to MODTRAN, a DOUBLING of the CO2 content will give rise to an extra absorption of the order of 0.5%- 1% of the escaping radiation (and not 8%).

In other words, the argument simplified, when made correct, is so much over-simplified, that it doesn't make a point anymore.

Because the problem is not there. The problem is rather: what will be the *effect* of this a priori small imbalance of incoming and outgoing radiation: how much does the Earth temperature have to rise in order to compensate for it. And THERE you enter in the twilight zone of feedbacks, soil responses, etc...

 

[ecofan]

Which proves his point even more strongly. There is some considerable OVERLAP in the certain bands of both CO2 and Water Vapor - meaning that he was already being very generous for the AGWer's. CO2 does not absorb all the IR anyway because Water Vapor absorbs some of it too RIGHT IN THE SAME 3 SLIM CO2 FREQUENCY BANDS! There is only a very small area where CO2 is totally free of Water Vapor overlap.

And if the available IR is already being absorbed to extinction, ( as most think it is ), then additional CO2 would be most welcome, to improve plant growth.

The more I look at it, this is an outstanding summary, and very conservative - even if it doesn't meet your standards for being so technically exact no layman could ever understand it. There's no gross error here anywhere... except to be exceptionally generous and deliberately err on the conservative side. That leaves him virtually immune to meaningful criticism except, of course, from individuals who are only interested in hearing the sound of their own voice.

 

[Art]

Which proves his point even more strongly. There is some considerable OVERLAP in the certain bands of both CO2 and Water Vapor - meaning that he was already being very generous for the AGWer's. CO2 does not absorb all the IR anyway because Water Vapor absorbs some of it too RIGHT IN THE SAME 3 SLIM CO2 FREQUENCY BANDS! There is only a very small area where CO2 is totally free of Water Vapor overlap.

And if the available IR is already being absorbed to extinction, ( as most think it is ), then additional CO2 would be most welcome, to improve plant growth.

The more I look at it, this is an outstanding summary, and very conservative - even if it doesn't meet your standards for being so technically exact no layman could ever understand it. There's no gross error here anywhere... except to be exceptionally generous and deliberately err on the conservative side. That leaves him virtually immune to meaningful criticism except, of course, from individuals who are only interested in hearing the sound of their own voice.

If I follow correctly IF CO2 absorbed 8% of Earth's IR then when the downstream effects (positive feedback etc) are factored in then the situation would be a whole lot worse than even the most ardent AGW proponents claim and so proving this number in itself does nothing to debunk AGW.

On the other hand although as Vanesch correctly points out most models of doom are based on a doubling of CO2, AGW folk claim the current 3% excess produced by man is already responsible for GW and climate change which seems highly unlikely.

An important question seems to be how quickly does CO2 re-emit it's photon of extra energy and in what wavelength. If this happens very quickly and the energy is converted into a form easily absorbed by other elements of the atmosphere which did not absorb it in it's original form then it seems CO2 is important beyond it's size in it's role as a catalyst?

 

[vanesch]

If I follow correctly IF CO2 absorbed 8% of Earth's IR then when the downstream effects (positive feedback etc) are factored in then the situation would be a whole lot worse than even the most ardent AGW proponents claim and so proving this number in itself does nothing to debunk AGW.

Yes, that was the point.

On the other hand although as Vanesch correctly points out most models of doom are based on a doubling of CO2, AGW folk claim the current 3% excess produced by man is already responsible for GW and climate change which seems highly unlikely.

Well, it depends. 3% since when ? As of now, I think the CO2 content is something like 375 ppm, and this has increased by more than 100 ppm in the last century. Even in the last 10 years, there has been a noticeable increase. It depends of course when you put the counter to 0, and what data you find reliable, but 3% would represent only 10ppm, which is certainly not the total observed CO2 increase.

An important question seems to be how quickly does CO2 re-emit it's photon of extra energy and in what wavelength. If this happens very quickly and the energy is converted into a form easily absorbed by other elements of the atmosphere which did not absorb it in it's original form then it seems CO2 is important beyond it's size in it's role as a catalyst?

All this shows that in order to really find out, you need to do quite a lot of detailed studies. There is NO SIMPLE ARGUMENT one way or another. The devil is in the details. This is why I consider the IPCC claims as "scientific fact beyond doubt" oversold, exactly because the whole issue is so complicated and delicate. But in as much as I think that the case is less evident than politicians want to make it sound, the opposite, that there is FOR SURE no AGW, is even less evident. It is not 3 simple lines on a sheet of paper that are going to prove beyond doubt that there is no AGW.

This is a horrendously complicated scientific problem, and a very interesting challenge.

 

[ecofan]

Strange, C02 levels were much, much higher 100,000 years ago, when there was a mile high layer of ice covering half of North America. Who do the AGW theorists blame that one on?

 

[mheslep]

... As of now, I think the CO2 content is something like 375 ppm, and this has increased by more than 100 ppm in the last century. Even in the last 10 years, there has been a noticeable increase. It depends of course when you put the counter to 0, and what data you find reliable, but 3% would represent only 10ppm, which is certainly not the total observed CO2 increase.

Its commonly known that measurements have been taken to tell how much of the C02 increase is man made, that is due to the burning of fossil fuels, and how much is due to natural causes, due to out gassing from warming oceans for instance. In this 'last 10 years' case are you sure the increase again has been checked for man-made vs natural? Yes or no, I often wonder in general when I see the CO2 updates quoted whether or not they are quickly grabbed from a raw partial pressure measurement or the required discriminator (some isotope measurement I assume?). In the last 10 yrs its obviously warmed so we'd expect natural increases in CO2 even if man made vanished.

 

[kamerling]

Strange, C02 levels were much, much higher 100,000 years ago, when there was a mile high layer of ice covering half of North America. Who do the AGW theorists blame that one on?

II think you are misinformed here. I don't think anyone believes CO2 was ever significantly above the preindustrial levels during any ice age in the last few million years. see here for example:

http://www.ncdc.noaa.gov/paleo/icecore/antarctica/vostok/vostok_co2.html"

There's a strong positive correlation between CO2 and temperature during the last 400,000 years at least, however with CO2 lagging up to 1000 years after the temperatures. The CO2
is probably produced when the ocean is warmer and taken up when it gets colder. This is believed to increase the severity of ice ages.

 

[kamerling]

Its commonly known that measurements have been taken to tell how much of the C02 increase is man made, that is due to the burning of fossil fuels, and how much is due to natural causes, due to out gassing from warming oceans for instance. In this 'last 10 years' case are you sure the increase again has been checked for man-made vs natural? Yes or no, I often wonder in general when I see the CO2 updates quoted whether or not they are quickly grabbed from a raw partial pressure measurement or the required discriminator (some isotope measurement I assume?). In the last 10 yrs its obviously warmed so we'd expect natural increases in CO2 even if man made vanished.

We produce more CO2 than the increase in the atmosphere, so the ocean is still taking it up .

 

[Andre]

There's a strong positive correlation between CO2 and temperature during the last 400,000 years at least, however with CO2 lagging up to 1000 years after the temperatures. The CO2
is probably produced when the ocean is warmer and taken up when it gets colder. This is believed to increase the severity of ice ages.

Well, if you scrutinize the details a bit, it may seem a bit different:

https://www.physicsforums.com/showthread.php?t=162192

 

[ecofan]

In the last 10 yrs its obviously warmed so we'd expect natural increases in CO2 even if man made vanished.

Actually, temperatures have been nominally flat for the past 8 years, except for this winter, which has been unseasonably cool.

 

[ecofan]

This just in:

Excerpt: Some 3,000 scientific robots that are plying the ocean have sent home a puzzling message. These diving instruments suggest that the oceans have not warmed up at all over the past four or five years. That could mean global warming has taken a breather. Or it could mean scientists aren't quite understanding what their robots are telling them. The buoys can dive 3,000 feet down and measure ocean temperature. Since the system was fully deployed in 2003, it has recorded no warming of the global oceans. "There has been a very slight cooling, but not anything really significant," Willis says. So the buildup of heat on Earth may be on a brief hiatus. "Global warming doesn't mean every year will be warmer than the last. And it may be that we are in a period of less rapid warming."

Interesting, since the story comes from the liberal NPR . Rest of article http://www.npr.org/templates/story/story.php?storyId=88520025"

 

[mheslep]

Actually, temperatures have been nominally flat for the past 8 years, except for this winter, which has been unseasonably cool.

Eh, unusually?

 

[kamerling]

Actually, temperatures have been nominally flat for the past 8 years, except for this winter, which has been unseasonably cool.

While it may be true that the temperatures have been flat for the past 8 years, because of the increases in previous years and the slow heat uptake of the ocean, you would still expect the ocean to become warmer. If it does not there must be something else going on.

 

[Gokul43201]

Actually, temperatures have been nominally flat for the past 8 years, except for this winter, which has been unseasonably cool.

I just looked at the recent data from NASA: http://data.giss.nasa.gov/gistemp/

I then compared the mean temperature anomaly during the period 1999 through 2001 (mean = +0.4833K) with that during the period 2005 through 2007 (mean anomaly = +0.7133K). I get an increase in mean temperature of 5.7K/Cent, which I think is actually significantly larger than the long-time average slope in the last couple decades.

How do you say the temperatures have been flat?

 

[vanesch]

Its commonly known that measurements have been taken to tell how much of the C02 increase is man made, that is due to the burning of fossil fuels, and how much is due to natural causes, due to out gassing from warming oceans for instance. In this 'last 10 years' case are you sure the increase again has been checked for man-made vs natural?

I wasn't talking about what was the origin of the CO2 (human or natural), nor whether it gave rise to any warming (or whether it was caused by any warming); just the observation that the amount of CO2 in the atmosphere did rise for more that 3% in the last century.

 

[vanesch]

In any case, when we see already here how involved the debate is, how easy one gets convinced by an erroneous argument, how complicated the interpretation is of the data, I wonder how a poor judge is going to "know the truth" in just a few hearings!

 

[mheslep]

I wasn't talking about what was the origin of the CO2 (human or natural), nor whether it gave rise to any warming (or whether it was caused by any warming); just the observation that the amount of CO2 in the atmosphere did rise for more that 3% in the last century.

Well if we're not interested in whether or not the CO2 source is natural then the whole subject is moot since we can't do anything about the source. (Other than for purposes of scientific curiosity).

 

[vanesch]

Well if we're not interested in whether or not the CO2 source is natural then the whole subject is moot since we can't do anything about the source. (Other than for purposes of scientific curiosity).

The discussions on the web pages of "debunkers of AGW" were trying to establish that the CO2 concentration has no influence at all on the thermal balance in the atmosphere ; one by trying to demonstrate that CO2 didn't absorb anything (or almost so), the other by showing that CO2 already absorbed everything it could, and that adding more to the atmosphere was not going to change the radiation balance.

In as much as I regret not seeing a detailed description of the physical processes taken into account in MODTRAN, I would take it as a more reliable radiation transport calculation, which shows us that a doubling of the CO2 content is responsible for a "radiative forcing" which is of the order of a to a few watts per square meter.

I don't think that trying to prove that CO2 doesn't do anything in the radiative balance of the atmosphere is going to work out, honestly. And from the moment that it does *something*, then everything comes down to careful calculation. We are talking here of a 1% effect. This means you have to be accurate on at least the promille level, and then you have to take into account all kinds of small details.

EDIT: BTW, if there is a positive feedback mechanism on the CO2 (for instance, by heating the oceans, they give off more CO2 etc...) and if this mechanism is significant, then in fact MOST of the CO2 increase we see in the the atmosphere is NOT going to be from human origin, but rather from this mechanism. If this is true, then we are already in deep doodoo because even if we totally stop our emissions today, we haven't gotten any handle on MOST of the increase.

 

[ecofan]

I don't think anyone is trying to say CO2 doesn't do anything... certainly there is BB absorption by CO2 and CH4. But the contribution appears to be relatively small compared to H2O and the whole impossibly complex cloud cover situation.

Frankly, I think we've been lucky that the past century or two has been nice and warm - we should be enjoying this interglacial period instead of trying to kill the warming trend with carbon offsets and other nonsense.

I see the latest sat photos show the Arctic Ice Cap now up to about 14 million square kilometers... even larger and reportedly thicker than the winter of 06-07, before the "catastrophic" breakup of the summer of '07 which caused Al Gore to predict the cap will be gone in 5 years.

I watched The Day After Tomorrow on DVD last week. Temperature dropped to minus 170 so fast the oil lines in some helicopters froze while ferrying the royal family somewhere. Seems there's a good side to all this after all.

 

[vanesch]

I don't think anyone is trying to say CO2 doesn't do anything... certainly there is BB absorption by CO2 and CH4. But the contribution appears to be relatively small compared to H2O and the whole impossibly complex cloud cover situation.

The way I understand this, AGW can be sliced in several components:
- the forcing by CO2, and the radiative effects of CO2.
- the origin of CO2, and the carbon cycle
- the climate effect of the radiative forcing, including a lot of feedback mechanisms
- the predicted evolution over a century of all of this, including human behaviour

I would say that in this list, we go from the pretty well established to the totally speculative, and the problem is that what matters is not whether certain effects exist, but rather, how numerically accurate all of this is. Because in the end, it makes a difference if we will warm or cool, and whether it will be 1 degree, or 5 degrees, or 25 degrees.

I'm trying to understand the argumentation from each side. I don't think anything has been shown for sure, either way. It is a pity that the debate is now so polarized, that one cannot have a open, scientific, inquiring discussion. I personally *would like to know* what is scientifically established, what is plausible, what is suggested, what are possible explanations, and what is totally open to speculation.