A guest post by Spencer Weart, in collaboration with Raymond T. Pierrehumbert
The simple physics explanations for the greenhouse effect that you find on the internet are often quite wrong. These well-meaning errors can promote confusion about whether humanity is truly causing global warming by adding carbon dioxide to the atmosphere. Some people have been arguing that simple physics shows there is already so much CO2 in the air that its effect on infrared radiation is "saturated"— meaning that adding more gas can make scarcely any difference in how much radiation gets through the atmosphere, since all the radiation is already blocked. And besides, isn’t water vapor already blocking all the infrared rays that CO2 ever would?
The arguments do sound good, so good that in fact they helped to suppress research on the greenhouse effect for half a century. In 1900, shortly after Svante Arrhenius published his pathbreaking argument that our use of fossil fuels will eventually warm the planet, another scientist, Knut Ångström, asked an assistant, Herr J. Koch, to do a simple experiment. He sent infrared radiation through a tube filled with carbon dioxide, containing somewhat less gas in total then would be found in a column of air reaching to the top of the atmosphere. That’s not much, since the concentration in air is only a few hundred parts per million. Herr Koch did his experiments in a 30cm long tube, though 250cm would have been closer to the right length to use to represent the amount of CO2 in the atmosphere. Herr Koch reported that when he cut the amount of gas in the tube by one-third, the amount of radiation that got through scarcely changed. The American meteorological community was alerted to Ångström’s result in a commentary appearing in the June, 1901 issue of Monthly Weather Review, which used the result to caution "geologists" against adhering to Arrhenius’ wild ideas.
Still more persuasive to scientists of the day was the fact that water vapor, which is far more abundant in the air than carbon dioxide, also intercepts infrared radiation. In the infrared spectrum, the main bands where each gas blocked radiation overlapped one another. How could adding CO2 affect radiation in bands of the spectrum that H2O (not to mention CO2 itself) already made opaque? As these ideas spread, even scientists who had been enthusiastic about Arrhenius’s work decided it was in error. Work on the question stagnated. If there was ever an “establishment” view about the greenhouse effect, it was confidence that the CO2 emitted by humans could not affect anything so grand as the Earth’s climate.
Nobody was interested in thinking about the matter deeply enough to notice the flaw in the argument. The scientists were looking at warming from ground level, so to speak, asking about the radiation that reaches and leaves the surface of the Earth. Like Ångström, they tended to treat the atmosphere overhead as a unit, as if it were a single sheet of glass. (Thus the “greenhouse” analogy.) But this is not how global warming actually works.
What happens to infrared radiation emitted by the Earth’s surface? As it moves up layer by layer through the atmosphere, some is stopped in each layer. To be specific: a molecule of carbon dioxide, water vapor or some other greenhouse gas absorbs a bit of energy from the radiation. The molecule may radiate the energy back out again in a random direction. Or it may transfer the energy into velocity in collisions with other air molecules, so that the layer of air where it sits gets warmer. The layer of air radiates some of the energy it has absorbed back toward the ground, and some upwards to higher layers. As you go higher, the atmosphere gets thinner and colder. Eventually the energy reaches a layer so thin that radiation can escape into space.
What happens if we add more carbon dioxide? In the layers so high and thin that much of the heat radiation from lower down slips through, adding more greenhouse gas molecules means the layer will absorb more of the rays. So the place from which most of the heat energy finally leaves the Earth will shift to higher layers. Those are colder layers, so they do not radiate heat as well. The planet as a whole is now taking in more energy than it radiates (which is in fact our current situation). As the higher levels radiate some of the excess downwards, all the lower levels down to the surface warm up. The imbalance must continue until the high levels get hot enough to radiate as much energy back out as the planet is receiving.
Any saturation at lower levels would not change this, since it is the layers from which radiation does escape that determine the planet’s heat balance. The basic logic was neatly explained by John Tyndall back in 1862: "As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial [infrared] rays, produces a local heightening of the temperature at the Earth’s surface."
Even a simple explanation can be hard to grasp in all its implications, and scientists only worked those out piecewise. First they had to understand that it was worth the trouble to think about carbon dioxide at all. Didn’t the fact that water vapor thoroughly blocks infrared radiation mean that any changes in CO2 are meaningless? Again, the scientists of the day got caught in the trap of thinking of the atmosphere as a single slab. Although they knew that the higher you went, the drier the air got, they only considered the total water vapor in the column.
The breakthroughs that finally set the field back on the right track came from research during the 1940s. Military officers lavishly funded research on the high layers of the air where their bombers operated, layers traversed by the infrared radiation they might use to detect enemies. Theoretical analysis of absorption leaped forward, with results confirmed by laboratory studies using techniques orders of magnitude better than Ångström could deploy. The resulting developments stimulated new and clearer thinking about atmospheric radiation.
Among other things, the new studies showed that in the frigid and rarified upper atmosphere where the crucial infrared absorption takes place, the nature of the absorption is different from what scientists had assumed from the old sea-level measurements. Take a single molecule of CO2 or H2O. It will absorb light only in a set of specific wavelengths, which show up as thin dark lines in a spectrum. In a gas at sea-level temperature and pressure, the countless molecules colliding with one another at different velocities each absorb at slightly different wavelengths, so the lines are broadened and overlap to a considerable extent. Even at sea level pressure, the absorption is concentrated into discrete spikes, but the gaps between the spikes are fairly narrow and the "valleys" between the spikes are not terribly deep. (see Part II) None of this was known a century ago. With the primitive infrared instruments available in the early 20th century, scientists saw the absorption smeared out into wide bands. And they had no theory to suggest anything different.
Measurements done for the US Air Force drew scientists’ attention to the details of the absorption, and especially at high altitudes. At low pressure the spikes become much more sharply defined, like a picket fence. There are gaps between the H2O lines where radiation can get through unless blocked by CO2 lines. Moreover, researchers had become acutely aware of how very dry the air gets at upper altitudes — indeed the stratosphere has scarcely any water vapor at all. By contrast, CO2 is well mixed all through the atmosphere, so as you look higher it becomes relatively more significant. The main points could have been understood already in the 1930s if scientists had looked at the greenhouse effect closely (in fact one physicist, E.O. Hulbert, did make a pretty good calculation, but the matter was of so little interest that nobody noticed.)
As we have seen, in the higher layers where radiation starts to slip through easily, adding some greenhouse gas must warm the Earth regardless of how the absorption works. The changes in the H2O and CO2 absorption lines with pressure and temperature only shift the layers where the main action takes place. You do need to take it all into account to make an exact calculation of the warming. In the 1950s, after good infrared data and digital computers became available, the physicist Gilbert Plass took time off from what seemed like more important research to work through lengthy calculations of the radiation balance, layer by layer in the atmosphere and point by point in the spectrum. He announced that adding CO2 really could cause a degree or so of global warming. Plass’s calculations were too primitive to account for many important effects. (Heat energy moves up not only by radiation but by convection, some radiation is blocked not by gas but by clouds, etc.) But for the few scientists who paid attention, it was now clear that the question was worth studying. Decades more would pass before scientists began to give the public a clear explanation of what was really going on in these calculations, drawing attention to the high, cold layers of the atmosphere. Even today, many popularizers try to explain the greenhouse effect as if the atmosphere were a single sheet of glass.
In sum, the way radiation is absorbed only matters if you want to calculate the exact degree of warming — adding carbon dioxide will make the greenhouse effect stronger regardless of saturation in the lower atmosphere. But in fact, the Earth’s atmosphere is not even close to being in a state of saturation. With the primitive techniques of his day, Ångström got a bad result, as explained in the Part II . Actually, it’s not clear that he would have appreciated the significance of his result even if he had gotten the correct answer for the way absorption varies with CO2 amount. From his writing, it’s a pretty good guess that he’d think a change of absorption of a percent or so upon doubling CO2 would be insignificant. In reality, that mere percent increase, when combined properly with the "thinning and cooling" argument, adds 4 Watts per square meter to the planets radiation balance for doubled CO2. That’s only about a percent of the solar energy absorbed by the Earth, but it’s a highly important percent to us! After all, a mere one percent change in the 280 Kelvin surface temperature of the Earth is 2.8 Kelvin (which is also 2.8 Celsius). And that’s without even taking into account the radiative forcing from all those amplifying feedbacks, like those due to water vapor and ice-albedo.
In any event, modern measurements show that there is not nearly enough CO2 in the atmosphere to block most of the infrared radiation in the bands of the spectrum where the gas absorbs. That’s even the case for water vapor in places where the air is very dry. (When night falls in a desert, the temperature can quickly drop from warm to freezing. Radiation from the surface escapes directly into space unless there are clouds to block it.)
So, if a skeptical friend hits you with the "saturation argument" against global warming, here’s all you need to say: (a) You’d still get an increase in greenhouse warming even if the atmosphere were saturated, because it’s the absorption in the thin upper atmosphere (which is unsaturated) that counts (b) It’s not even true that the atmosphere is actually saturated with respect to absorption by CO2, (c) Water vapor doesn’t overwhelm the effects of CO2 because there’s little water vapor in the high, cold regions from which infrared escapes, and at the low pressures there water vapor absorption is like a leaky sieve, which would let a lot more radiation through were it not for CO2, and (d) These issues were satisfactorily addressed by physicists 50 years ago, and the necessary physics is included in all climate models.
Then you can heave a sigh, and wonder how much different the world would be today if these arguments were understood in the 1920’s, as they could well have been if anybody had thought it important enough to think through.
For Further Reading
References and a more detailed history can be found here and here.
Some aspects of the "thinning and cooling" argument, and the importance of the radiating level are found in the post A Busy Week for Water Vapor, which also contains a discussion of water vapor radiative effects on the top-of-atmosphere vs. surface radiation budget. A general discussion of the relative roles of water vapor and CO2 is given in Gavin’s post on ths subject.
You can get a good feel for the way CO2 and water vapor affect the spectrum of radiation escaping the Earth by playing around with Dave Archer’s online radiation model here. It would help, of course, to read through the explanation of radiating levels in Archer’s book, Understanding the Forecast. A discussion of radiating levels for real and idealized cases, at a more advance level, can be found in the draft of Pierrehumbert’s ClimateBook; see Chapters 3 and 4.
The Monthly Weather Review article commenting on Ångström’s work is here, and Ångström’s original article is here.
In response to:
…and…
Well, the Georgii quote you(Timothy) provided said quite the opposite, and that there was a decrease in CO2 ppm moving upward and that it was not consistently mixed: “The marked decrease of the CO2 concentration in the lower stratosphere compared with the upper troposphere suggests that, contrary to previous practice, it is wrong to assume a constant mixing-ratio of CO2 in the troposphere and stratosphere.”
But I was more curious as to whether there was a smooth, linear decrease with altitude rather than with a sudden drop.
[Response: There’s a detectable drop in CO2 as you go into the stratosphere from the troposphere, because it takes some time to mix it upward. There’s also a detectable interhemispheric difference in mixing ratio in the troposphere. These are all very interesting for what they tell us about mixing and about sources and sinks, but the variations in mixing ratio are too small to be of much importance for radiative transfer. –raypierre]
re: #32
Money certainly helps, but that’s ill-informed about farming, because cost-effectiveness matters, a lot.
But, this leads me to a question/suggestion for RC: given the highly multi-disciplinary nature of climate science, maybe it would be good to recruit an expert guest poster who could talk about the intersection of climate science with agricultural/bioscience research/ag engineering, etc …
For instance, my alma mater Penn State has a large College of Agricultural Sciences: http://www.cas.psu.edu/
Maybe Prof. Mann knows somebody relevant there.
5 minutes’ rummaging found “Predicting Pests”:
http://aginfo.psu.edu/PSA/07WinSpr/Pests.html
“entomologist Dennis Calvin and his research team look at how climate and weather influence the timing of insect emergence in field crops.”
“Asian soybean rust… needs green soybeans or kudzu leaves to grow, and therefore it can survive only in the deep South, where winters are warm…We speculate that in years when the deep South has a warm and wet spring, this pathogen will be a serious widespread problem.”
Here in CA, UC Davis is quite strong, and there are of course many schools with fine programs, as many American land-grant universities started as ag schools, and many bioscience and environmental departments have some heritage there. Really, agricultural research is way beyond “throw infinite money at the problem”, which doesn’t work.
Anyway, we should keep biology out of the physics discussions, but maybe a little more well-informed biology discussions would be relevant to RC?
Regarding this (5th. paragraph) action summary =>
“What happens to infrared radiation emitted by the Earth’s surface? As it moves up layer by layer through the atmosphere, some is stopped in each layer. To be specific: a molecule of carbon dioxide, water vapor or some other greenhouse gas absorbs a bit of energy from the radiation . . . (so that) . . . the layer of air where it sits gets warmer. The layer of air radiates some of the energy it has absorbed back toward the ground, and some upwards to higher layers. . . . Eventually the energy reaches a layer so thin that radiation can escape into space.”
—- I’m a little surprised that there is no mention of the governing equations for this absorption/re-radiation: the (1905/06) Schuster-Schwartzchild Equations of Transfer.
I have an evalaution set out in this article => Essenhigh, R.H.: Prediction of the Standard Atmosphere Profiles of Temperature, Pressure, and Density with Height for the Lower Atmosphere by Solution of the (S-S) Integral Equations of Transfer and Evaluation of the Potential for Profile Perturbations by Combustion Emissions. Energy and Fuels: 20, 1057-1066 (2006)
DaveS (#51) wrote:
Sorry – I was in a hurry – at work at the time.
Something slightly more recent…
In this context, “roughly constant” or well-mixed would seem to be a good approximation – as ppm would have been above 300 ppm, I presume, and we are speaking of its effects being logarithmic.
Then the make the same point that raypierre made regarding the lag:
Five year lag – through tropical upwelling.
Anyway, my apologies about quoting abstracts on this topic, but this doesn’t seem to be a “hot topic” anymore, and abstracts are all I have. (I am not in the field, but work as a coder for software that tracks cell phone network performance.)
Couple of questions. First, can you show (on the graph in Part 2) the lines for 8x and 16x increases in CO2? That would go very far in clarifying the nature of the relationship.
Second, is it true that heat is radiated from atmospheric GHG molecules at different wavelengths than it was aborbed? If so, how does this affect the how the radiated energy is absorbed by other molecules? Is the difference constant or does it vary by some other factor?
#33 Barton Paul Levnson:
If memory serves me, Henry Bauer said one of Immanuel Velikovsky’s early forays into science involved him assuming that gases were stratified by molecular weight, and a fairly stubborn refusal to accept correction on the issue :)
This is great, as a recent Science article raised the issue, or complaint, that IPCC global warming models did not address the stratosphere but only the troposphere. What would be the difficulties in amending those models to include activity in the stratosphere?
[Response: Almost all the models have a stratosphere of some sort, though there are not generally enough points in the stratosphere to satisfy professional stratospheric dynamicists. Probably the article was complaining not so much about the modelling itself as the degree of attention paid to the influence of what is going on in the stratosphere. As long as you’re not talking about adding in chemistry, most models can improve their representation of the stratosphere simply by adding in more points in the vertical, which isn’t even that expensive computationally. The relative importance of stratospheric processes in tropospheric climate change is a matter of some debate. –raypierre]
There is different band saturation argument going around. This argument goes, if I understand it correctly, that the rate of energy transfer for CO2 is saturated. I think that means that the ratio of transmitted radiation to incident radiation isn’t constant as a function of incident radiation intensity at the levels present in the atmosphere because CO2 can’t transmit energy fast enough either by collisional deactivation or emission. My gut feeling is that this is total BS because I suspect the energy density in a basic IR spectrometer is orders of magnitude higher than that from the surface of the earth, and I don’t think Beer’s Law is violated then. Are you familiar with this argument and is there a quick and dirty answer?
[Response: I hadn’t heard this argument before, but your gut feeling is right. Laboratory spectroscopy that is used to feed the HITRAN archive is done in conditions similar to those prevailing in the atmosphere, and if there were some problem of the sort you mentioned, it would be seen already in the spectrometers. –raypierre]
Very interesting. Thanks for exposing yet another gimmick.
Thing is, it doesn’t matter that it’s wrong, so long as it’s convincing enough that you can manufacture a public sense of uncertainty about the basics of the greenhouse effect.
A two-layer (surface and core separated by opaque gas) model for the Sun doesn’t work too well either, but nobody would be crazy enough to suggest that it should. On the other hand, it is well-known and established for the better part of a century that changing opacities in one place can have profound effects on conditions elsewhere (such as the core). There’s nothing controversial about it, but then again, there’s no big corporate interest trying to persuade us that we got our rad transfer all wrong in that case.
Hey, I checked out Lubos Motl’s page – He’s clearly a very smart person, but he should stick to stuff he knows. Typical theorist.
Notice that Motl doesn’t actually set up a model with multiple layers and numerically solve the radiative transfer problem; he’s really just doing a back-of-the-envelope calculation. String theorists as a rule tend to think that if you can’t solve something analytically it’s not worth solving.
I try to avoid ad hominem, but geez, it really is awfully smarmy to bash Weart with a statement like “It is not that difficult and a good physicist knows how to solve the differential equations that arise in this context.” (re the effect of many layers of CO2, versus a simple one-layer model), AND THEN not to bother either to write down the relevant differential equations, much less solve them! Talk about being a hypocrite! I know some theorists think that if it’s not Yang-Mills or twistor theory then it’s mathematically trivial, but hey Motl, perhaps you could pick up a copy of Chandrasekhar or Mihalas & Mihalas and go teach yourself some plane-layer radiative transfer methods before you go off making such a fool of yourself again. Yes, you do in fact need to know more than just the total column density of CO2, unless you just like to solve Fermi problems.
This is a little bit off-topic, but perhaps not. At glacial maximum, with the oceans three hundred feet lower, is there any effect on the atmosphere? At the Dead Sea, I’ve heard that the atmosphere is much denser, but that is an isolated pocket. Is there any correlation between global climate and sea level?
[[A quick question: I occasionally run into the argument that the 0.7 degrees C warming observed as CO2 levels have increased from 273 ppm to 383 ppm suggests a lower climate sensitivity, because we are already 40% of the way to a doubling of pre-industrial CO2 levels and we would expect greater radiative forcing changes to occur from the initial addition of CO2 given the relationship between CO2 and wavelength absorption described in this post.
The obvious answer is that we are not currently at the “equilibrium” temperature that would accompany a 383 ppm CO2 concentration due to the thermal inertia of the ocean, but am I missing anything else? Also, is there a good chart available of the best guess equilibrium temperatures associated with different levels of CO2? ]]
The argument assumes that there are only two factors involved, CO2 and temperature. In reality several factors are involved. Negative forcings like sulfate aerosols and volcanic eruptions have caused some cooling. The point you raise is also valid; some of the warming is still “in the pipeline” and will show up (is already showing up) in the future.
[[So, he wondered, is anyone aware of any calculations regarding what might happen if over a billion hydrogen powered cars were all operating and expelling water vapor? Would this cause an increase in GHGs that would rival the problems we see with CO2? What about local humidity rates, that sort of thing?]]
It wouldn’t matter, because water vapor rains out quickly, on average in 9 days, whereas CO2 stays up an average of 200 years.
#63
Been wondering whether to post this as it sounds like I’m a snide sceptic but a billion H2 powered cars continuously emanating water vapour? Not taking a break for 9 days? Ah well, answering my own question, if it did become a problem I suppose the WV could be condensed at source.
Keep posting Barton as I do look out for yours.
Re #63 A billion cars producing H20
I can see that there would be no problem with H2O, but what about leakage of hydrogen on a massive scale?
RE 62: “The point you raise is also valid; some of the warming is still “in the pipeline” and will show up (is already showing up) in the future.”
The point is frequently made that the oceans delay atmospheric temperature rise, so that the rest of the expected air temperature increases are in the pipeline and will be coming shortly. This is logical as the atmosphere is well mixed and in contact with the ocean. I live near the cold ocean in the Gulf of Maine and can attest to the cooling impact it has on air temperature. We also are well aware of the 800 to 1,000 year “delay” in the co2 response to air temperature as depicted in the long-term ice core data. The thought there being that co2 is released from the ocean as the ocean warms, but it takes 800 to 1,000 years to fully warm. My question is: Is the warming that is in the pipeline going to take 800 to 1,000 years to play out? If so, it does not appear to be a significant factor in the warming to occur this century. I have never seen an estimate of the delay relative to this century.
Sam (#66) wrote:
The following should give you a few figures. For example, according to our calculations, 50% of the temperature rise should occur within the first twenty-five years.
[[I can see that there would be no problem with H2O, but what about leakage of hydrogen on a massive scale?]]
Might be a fire hazard in the immediate vicinity, I suppose.
[[The thought there being that co2 is released from the ocean as the ocean warms, but it takes 800 to 1,000 years to fully warm. My question is: Is the warming that is in the pipeline going to take 800 to 1,000 years to play out? If so, it does not appear to be a significant factor in the warming to occur this century. I have never seen an estimate of the delay relative to this century. ]]
I think the release in a normal deglaciation takes that long because the temperature changes that drive it take that long — the slow changes in Earth’s orbit and axial tilt that drive ice age/deglaciation cycles. In the present case, we’re warming up the Earth many times faster than that, so we could have problems with ocean-released CO2 much faster.
Re #65:
I read a report a couple of years ago claiming that H2 is an ozone-destroying molecule, so if the “hydrogen economy” emerges, it will wreck the ozone layer.
Is lubos Motl actually a real scientist or a highly educated politically motivated scientific activist ?
He seems to pretend to know but does he know ? Being based at a prestigous university you would conclude that he was a intelligent and objective individual but he sound somewhat politically motivated to me.
Re #67. The reference is:
Potential Environmental Impact of a Hydrogen Economy on the Stratosphere
Tracey K. Tromp, Run-Lie Shia, Mark Allen, John M. Eiler, Y. L. Yung
Science 13 June 2003: 1740
Abstract:
“The widespread use of hydrogen fuel cells could have hitherto unknown environmental impacts due to unintended emissions of molecular hydrogen, including an increase in the abundance of water vapor in the stratosphere (plausibly by as much as ~1 part per million by volume). This would cause stratospheric cooling, enhancement of the heterogeneous chemistry that destroys ozone, an increase in noctilucent clouds, and changes in tropospheric chemistry and atmosphere-biosphere interactions.”
This abstract is available, with some references to the article, at:
http://www.sciencemag.org/cgi/content/abstract/300/5626/1740
The authors apparently admit the effect described depends on how much H2 would get absorbed into the soil. Critics say they greatly overestimated likely leakage rates. I suspect the whole question is moot because of the infrastructural costs of switching to hydrogen-fueled cars – either plug-in-anywhere hybrids, or battery-driven cars with battery-swap stations are probably better bets. Less private car use even better.
# He is a real scientist and a quite talented one, but on his site, describes himself as a “reactionary physicist”.
It seems to have all started when the former Dean at Harvard, Laurence Summers was replaced for making statements to the effect that women weren’t as good at science as men and not supporting positive action on entry to courses.
Motl painted himself into a bit of a corner by supported Summers and has adopted increasingly ‘politically incorrect’ statements ever since. I thinks he’s nearly applied 16 coats by now.
He’s been described as the “string enforcer” by certain elements in the physics community, who find his method of debate a bit over the top. He’s usually regarded as a bit of a troll on their web sites nowadays.
I’m not sure of his current relationship with Harvard University, but he seems to be devoting an awful lot of time to supporting the denialist camp in the AGW debate.
Heaven only knows why…
Barton Paul Levenson (#68) wrote:
There exist materials for the safe storage of hydrogen in relatively compact space. I could look this up a little later if nobody beats me to it. Additionally, hydrogen burns at a lower temperature than gasoline – and it does tend to float and get dispersed by the wind rather than pool at the surface or remain on one’s clothes while it burns.
Re my #72: sorry, when it says “Re #67” it should say “Re #70”.
Re #72,
Thanks for digging up that citation, Nick!
Timothy Chase wrote: “There exist materials for the safe storage of hydrogen in relatively compact space.”
Here is an example from ECD Ovonics, who also manufacture thin-film amorphous silicon photovoltaics:
My memory and knowledge are fuzzy, but I have a couple of questions on H2-powered vehicles I need clarifying. To be effective doesn’t the H2 need to be manufactured on board as needed from hydrocarbons, and isn’t that process currently too slow, energy intensive, and cumbersome for that? If pure H2 is stored (in liquid form??) on the vehicle it seems the fire/explosive hazard would be prohibitive, but, more significantly, wouldn’t the “gas tank”, to handle the high pressure, need 2-4 tons of thick high-grade steel? Wouldn’t all of this make H2 a non-starter? Or am I way behind the times and science?
I find it somewhat amusing that the arguments espoused by denialists today were effectively scuttled half a century ago. It seems more and more true that some skeptics, to quote Gavin regarding Dr. Lindzen, are fighting yesterday’s battles. This article brings that comment into detailed relief.
This is exactly where RealClimate can make a difference, by posting clear, well-developed and well cited explanations in laymans’ terms, which in some cases such as this directly address specific skeptic arguments, and which allow interested “civilians” the opportunity to satisfy themselves that this isn’t all just “guesswork”, and that perhaps there is substantive reason to believe that we can be highly confident of global temperature forecasts.
Of course, there is still much more ground to cover, such as: how do we know precisely how much CO2 is abosrbed by the oceans; when will saturation occur there; what will the short and long term effect be on climate based on that process. Also needing better explanation: does the planet “react” to the greater presence of CO2 and “make use of it”? In other words, is the carbon cycle expanding? Is that even a coherent question?
This article is potentially historically important because it sets a tone for further discussion. I can easily envision it as part of a series, a primer which covers the basic issues with regard to AGW and which does so in a simple yet reliable way.
Bravo.
The problem I have is that a Havard string theorist like Lubos http://motls.blogspot.com/2007/06/realclimate-saturated-confusion.html
can write a plausible critique of your work and people will accept it because he is a scientist. Now how do I know who is correct? With my lack of qualifications in any of the disciplines how do I know what is the correct science?
In reading the two articles I do notice one striking difference. The RC article from Spence and Ray includes copious references to other people’s work and includes no implied or otherwise insults to other researchers.
Lubos on the other hand, as I read it, seems to think that just because he can understand differential equations that he is correct and everyone else is wrong. Lubos in following comments also disparages consensus as being weak however to me other people confirming what you are saying with peer reviewed work is a sign, at least to a layperson such as myself, that you have a greater chance of being correct.
The radiation budget of the Earth is a very difficult subject and contains many non obvious traps for beginners that I thing even a string theorist can fall into. Just because you understand strings does not mean that the subject of radiation is easy.
Again thank you Spencer and Ray for your contribution to helping the understanding of science challenged people such as myself. I know which one has the greater chance of containing at least what truth we know of with our present knowledge.
[Response: Your warm words are very encouraging. Thanks so much. Spencer deserves all the credit for initiating this article,and without his clear prose and historical perspective it would not have been nearly as effective at communicating the things that needed to be said. –raypierre]
One reason this debate can be hard to follow is that there’s a lack of explicitness as to what you are and are not arguing. In particular, if I’m reading right, you’re *not* disagreeing with the claim that each additional carbon dioxide molecule makes less of a contribution to warming than the one before (at least, putting aside potential non-linear positive feedbacks unrelated to radiation). Indeed, my Harvard “atmospheric physics” professor explicitly made this claim while lecturing on radiative transfer, so I presume it’s uncontroversial.
[Response: That’s right. That’s completely uncontroversial, and the effect is incorporated in every radiation model at least since Manabe, and more probably since Plass. If it weren’t for this effect, there probably wouldn’t be any habitable planets at all, since modest fluctuations in CO2 would lead to lethal swings in climate –raypierre]
You *are*, however, disagreeing with the claim that each additional carbon dioxide molecule makes no contribution to warming whatsoever. But is any serious source actually making that argument? Lubos Motl, for example, is not. (Of course, in characteristic “Lubos” fashion, the lack of a concrete disagreement hasn’t stopped him from enthusiastically insulting your intelligence :-D)
[Response: It’s often quite hard to tell just what Motl is saying, and frankly I don’t waste much time paying attention to his blog. Others report that he seems to be claiming that the warming effect of CO2 will saturate before long, and that claim certainly resurfaces from time to time among the skeptics community. I myself thought the argument had died out completely, but Spencer reports that on his blog he had been getting repeated questions about saturation. Anyway, it’s irrelevant what Motl thinks, since this post is not a response to anything in Motl’s blog, regardless of what Motl says. I wasn’t even aware that he had written anything about this subject until I saw his blog show up on the Technorati blog-response tracking for our post. –raypierre]
Re #68, #72, #77 and others: H2-economy
Thanks you all for your answers.
I was not that concerned about explosion hazards: I remember a Dutch study where it was shown that as far as cars were concerned H2 did not have to be more dangerous than gas (= LPG/LNG), which was in use already.
It seems we have to be more concerned about the destruction of the ozone layer (again) by leaking H2.
All this quite apart from the fact that H2 is NO energy source and hence no magical cure for our energy problem.
#60 “He’s clearly a very smart person, but he should stick to stuff he knows. Typical theorist.”
And here we have a quote: “Although I consider myself primarily a theoretician…” from none other than our esteemed co-author.
sorry couldn’t resist!
[Response: I myself wouldn’t describe Motl’s distortions as being in any way typical for a theorist. Of course, any good theorist needs to have a very sound understanding of data. I also don’t think it’s a matter of sticking to things one understands. The kinds of physics we are talking about are easily understood, on a full quantitative level, by anybody with an undergraduate physics degree, or indeed with high-school AP physics. On a sound non-quantitative level, they can be understood more broadly. A person with Motl’s background should be able to comment intelligently about these issues, but when somebody with the capability to understand the system fails to do so, there’s something rotten in Denmark.
Somebody earlier raised the question of how to know which authority to believe. It’s perfectly valid to look at what institution a person was hired at, and ordinarily being hired by the Harvard physics department should lend some weight to ones opinions about things in physics. Even Harvard makes mistakes, though (and the word on the web is that this particular mistake may be in the process of rectifying itself), so one must look beyond just a person’s pedigree. A good place to start is to look at what people have published, in what journals, and how recently. Peer judgment is also worthwhile, so looking at what panels a person has served on is useful. In the end, while some things need to be accepted on authority, there’s really no substitute for actually understanding the scientific arguments, and in a democracy, it’s incumbent on scientists to try to make the arguments comprehensible enough that one doesn’t need to lean too much on pure authority. –raypierre ]
I’m not sure if Lubos isn’t a Sokalian hoax. Has anybody seen him in reality?
My memory and knowledge are fuzzy, but I have a couple of questions on H2-powered vehicles I need clarifying.
I believe Iceland have had H2 powered vehicles and infrastructure for several years, you could probably check out the problems and solutions they have achieved in the last decade or so. Probably getting a bit off track here to go into any details though, and its not hard to find information on it.
Good explanation that even non-scientists can understand.
I think it’s interesting the contradictory arguments denialists make. On the one hand they say the atmosphere is saturated with CO2 & H20, so no GW, and on the other they say how can something as small as a few parts per million make any difference? I’ve seen denialists who make both arguments simultaneously.
Then some go on from “GW is not happening” to “it’s happening, but it’s good for us…warming helps agriculture.” They are all over the board.
“Moreover,the “thinning and cooling” argument — that the brightness temperature depends only on the layer from which radiation escapes to the observer — is absolutely standard stuff in physics. The core of the Sun is some tens of millions of degrees. You don’t see that when you look at the sky, do you? The core of the Earth is several thousand degrees. You don’t see that when you look at the ground, do you? It would be incandescent if you did. You don’t see it because you see radiation at the temperature of the level from which the radiation can escape. It’s that simple. Atmospheric IR is no different. If you are used to the “photosphere” of the sun, just think of what we’re talking about as the “IRsphere” of the Earth.”
There is one big problem with this concept: the photosphere of the earth contains huge windows from which IR can directly escape from the surface, That is also the reason why deserts cool so fast at night. You can see the surface of the earth in the infrared thermal window.
[Response: The concept is fine if you apply it in individual wavelength bands. The “photosphere” for 6 micron IR is at a different height from that for 15 micron IR. –raypierre]
Re #81 Where Ray wrote:
[Response: That’s right. That’s completely uncontroversial, and the effect is incorporated in every radiation model at least since Manabe, and more probably since Plass. If it weren’t for this effect, there probably wouldn’t be any habitable planets at all, since modest fluctuations in CO2 would lead to lethal swings in climate –raypierre]
It is not completely uncontroversial. I am arguing that because it is saturated (optically thick) then adding more CO2 will cause the saturation to be closer to the surface. This means that the surface warming due to CO2 will increase in direct proportion to the CO2 concentration, rather than with the logarithm of the concentration as the current models predict.
Twixt Plass and Manabe, Fritz Moller found “almost arbitrary temperature changes” and that “Very small variations [in water vapour feedback would] effect a reversed sign or huge amplification. We know that the atmosphere does not react in this way.” However, since Moller wrote that, we now know that rapid climate change does happen, and that Venus has suffered a lethal swing in climate!
Re 80: Ender, I don’t see how there can be any question. Motl may or may not be a brilliant string theorist, but he is not an expert on climate, on infrared spectroscopy or any other field relevant to these studies. I am a physicist, too. You want to know about radiation, I’m your guy. I can get by in discussing semiconductors, the space environment, spacecraft design, manufacture of electronics… Here, I am a rank amateur. The fact that I’m a physicist and have solved the hydrogen atom and harmonic oscillator problems helps. And the fact that I’ve looked at how energy lines in atoms become energy bands in solids has been invaluable in seeing how the behavior of CO2 as a gas behaves differently than a single CO2 molecule. But the point is that I have made a significant effort in recent years to understand these things. I suspect Professor Motl has not. Certainly, it is not reflected in his arguments, which are naive. Science places great value on expertise. The opinions of a scientist usually carry little weight in scientific circles where that expertise does not extend. Motl’s arguments matter about as much as flatulence in a windstorm.
PS to my post above…
If you are looking at the wavelengths, the peaks are at 20 mu-m, 22.5 mu-m and 25 mu-m, which I presume are exactly what you would expect.
People can check this for themselves.
[Response: Yes, infrared spectroscopists generally work in wavenumber in units of (1/cm). In the Part II graphs I plotted things as a function of wavelength instead, since I figured wavelength is a more familiar quantity. –raypierre]
RE: #81
raypierre (and Spencer)
Steve asked “You *are*, however, disagreeing with the claim that each additional carbon dioxide molecule makes no contribution to warming whatsoever. But is any serious source actually making that argument?”
Is any serious source actually making that argument?
I myself do not, but still as climate sensitivity is given in degrees per doubling of CO2, would find it more to worry about the CO2 that is already out there, rather than any we are going to emit in the future.
Perhaps that’s the point that get oversimplified when people casually suggest that “saturation” has been reached.
Alastair, when Ray writes “uncontroversial” I would guess Ray likely means “uncontroversial in published science on the subject” —- why not write the paper you’re promising? If you do the math and do change the opinion of contemporary physics on this question, that will elevate your belief above the many handwaving arguments, political statements, and other opinions that get dropped in here by nonscientists. Without the math, none of those are ‘controversy’ on the scientific question, eh?
Re #88: [we now know that… Venus has suffered a lethal swing in climate!]
Do we in fact know this? Perhaps I’m quibbling, but I think it’s an interesting question: did Venus in fact experience a “swing” – that is, an extreme change from a perhaps more Earthlike climate – or did it simply evolve towards its present state from its primordial state?
On the other hand, we do know that Earth once underwent a massive change in atmospheric composition, the switch from a reducing atmosphere to one dominated by oxygen. And what’s more, we know this was caused by the actions of living things. Which should be a good response to the “humans are too puny to affect the whole Earth” line of reasoning :-)
#60, #83, #89:
When I say “He’s clearly a very smart person, but he should stick to stuff he knows. Typical theorist.” (re. Motl), I am speaking as a theoretical physicist myself. So it’s only a tongue-in-cheek attack on theorists. :)
There’s a tendency for SOME hothead pencil-and-paper theorists to trivalize physics-related problems outside their own narrow field. You’d be hard-pressed to find an applied/numerical physicist who’d disagree with this.
Say you have a friend who’s a radiologist. Maybe you ask him/her in private about your heart condition. If you’re friend’s not an arrogant *****, they’ll offer general advice but tell you that you should really ask your cardiologist. Don’t be surprised, though, to find the occasional young brilliant but hothead radiologist who somehow thinks he/she is an expert in other fields of medicine. Same goes for every other professional subfield. Common sense tells you to ignore these people when they are speaking outside their areas of expertise.
Rad transfer is important in atmospheric physics, astrophysics, nuclear weapons design, and so on. Not string theory. There are any number of experts on radiative transfer, of any political stripe you care to pick. Motl is not one of them.
Besides, again, he didn’t actually write down the diff eq’s and solve them; he just waved his hands a lot. That might be good for partial credit but it’s not a full answer, sorry. I haven’t solved the transfer myself for this problem either, but I know enough to know what I don’t know (at least in this case), which is more than I can say for Motl.
Re #92
Hank,
You are quite right! I should have added a smiley when I implied that there was a school of scientists supporting my ideas :-)
You are also right that I should write my paper, and stop my jousting here. But as Timothy wrote I still have a lot to learn. As Donald Rumsfeld said:
“There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don’t know. But there are also unknown unknowns.”
This is a good place to find answers to my unknown unknowns. For instance, if you want to find out why Prof. Ray Pierrehumbert, Goody & Jung, and Einstein were wrong about greenhouse gases radiating according to Planck’s function, then you have to google for the “equipartition theorem” not “Boltzmann distribution” as I had thought!
Anyway, in the words of Tony Blair may I say to you all au revoir, auf Wiedersehen and arrivederci!
Re. 86 (Lynn V)
I am what YOU would call a ‘denialist’. Denialist of what? I happen to be sceptical with regard to the threat of AGW. You use the term ‘denialist’ as if it means the denial of truth. Its true that irrational and arrogant arguments are presented by sceptics. But this is equally true of many AGW advocates. It is wrong to present the irrational arguments as representative of all sceptics. I care about the natural environment as much as you do. I totally support a reduction in use of energy and natural resources (especially water). I support the use of walking, cycling or public transport where possible. I detest 4x4s (SUVs) in urban environements, etc, etc. It seems however that a support of AGW theory has become a benchmark of whether you care about the environment. This is certainly true for Euroepan politicians. However, as a scientist, I am not going to say I believe something just because its ‘popular’ or polictically correct. In contrast to many commentators on this blog, scientific truth is not defined by how many peer-reviewed articles you have published or can quote. Here is an analogy for me. At school you are meant to believe all the teacher tells you and all you read in the text books. These are the ‘experts’. But when you progress to science at university, you are encouraged to understand the arguments and to question, and in particular to not assume that the ‘expert’ writer is always correct. Science would not progress and evolve if we did not question and challenge. When I read a scientific paper or artical, I expect the arguments to be convincing. When I feel they are not, I believe I have every right to challenge the view given. My reasons for scepticism regarding AGW are straight forward:
1. The view that current temperatures are warmer than at all times in the past 2000 years is unconvincing. IPCC itself highlights the uncertainties regarding evidence from more than about 500 years ago.
2. The view that temperatures are rising more rapidly than ever (ie. in human history) is unconvincing. The current trend is no more significant than experienced during the first half of the 20th century, when ‘dramatic’impacts what not noted.
3. Its true that the world is warming and that ice is melting and glaciers receding, etc, but there is nothing to indicate this is anything other than a response to natural changes.
4. While the current trend does not corelate well with sun activity, the view that CO2 emissions are the ONLY explanation is unconvincing.
5. Many, many people (including many I know) are convinced that extreme weather is becoming far more common. This is in very large part due to modern communications whereby we routinely see floods, droughts, storms, etc on our TV screens whereas, say 20 years ago, we didn’t. The view that there is statistically increasing trend linked to glbal warming is unconvincing.
6. Its strange to me that ‘climate change’ is commonly presented as the biggest threat facing mankind. It remains a theory. There are very real problems facing mankind, such as millions dying every year of poor drinking water, malnutrition, malaria and Aids. We could really do more to deal with these. The problem is that they are not problems of the developed world. Climate change seems to be affecting us (although WE argue that its the poorest countries who will be affected most). To me, worrying about climate change is basically self-indulgent. There are truly bigger and more certain problems out there we could do much more to help with.
And just to return to whether its reasonable to question the ‘consensus’science. If you look at the link I provided in 17, you can view reviewers comments on various IPCC drafts. Now, I would assume all of the reviewers were invited by IPCC on the basis that they are respectable experts who are qualified to comment. If you look at this, you will see many comments that do not agree with the supposed concensus. The final conculsions are not unanimous. While this may represent a majority view, it is incorrect to claim there is no debate and there is complete concensus.
All the best.
Re 86 Lynn Vincentnathan: “I think it’s interesting the contradictory arguments denialists make…. They are all over the board.”
That’s because they are not at all interested in following where the science leads and basing their conclusion on what it tells them, but in finding every possible argument and data point, no matter how tenuous, to support the conclusion that they have already made, namely that it is not happening. As a result they keep latching on to factoids such as the warming on Mars, or the increased reflectance of Pluto, or the 800 year CO2 lag, or CO2 saturation without critical thought.
I’ve encountered exactly the same process in non-scientific controversies. Not only are the same type of self-authoritative, tautological, straw-man and red herring arguments used, but more important, when a number of diverse people who have in common only their opposition to some thing or other coalesce solely to argue or fight against it they almost never can agree with each other on what they are for. When asked to propose an alternative idea or course of action they instead begin to argue amongst themselves. While they are fighting the fight, the contradictions simply don’t matter, kind of in the “the enemy of my enemy is my friend” way.
Document http://www.metoffice.gov.uk/climate/uk/about/UK_climate_trends.pdf gives the observed Trends in the UK climate.
It is a very good document, easily understood and is of the highest quality.
It shows quite clearly that the climate of UK is changing, and some of the parameters measured are unprecedented in the series recorded.
In particular sunshine amounts and temperature show a matching upward trend from 1987 (fig 3 and fig 15)and both have reached record unprecedented levels at the end of the series in 2003/4. And my subjective observations are that the Matching Trend continues upwards for 2005/6.
The exact correlation between sunshine amounts and temperature, region by region, is so perfect that I have had to read it several times to make sure I wasn’t making a mistake.
The scientific consensus is that this observed warming of surface temperature in UK is due to secondary infra red absorption/excitation of a tri-atomic molecule ( CO2) high in the Troposphere, and that the direct warming caused by the extra sunshine is not important, I find it difficult to fit this consensus view with the actual observations.
If there are less clouds, this must be a strong indicator of less moisture (water vapour) in the atmosphere, which would reduce the greenhouse effect and so we should actually be getting colder.
The report only says that the observed results match the models, but does not go any further and tell us what model and why it fits, and says further work will take place on analysing inter-relationships.
Can anyone help and explain why the simple prosaic reason is that its getting warmer because its getting sunnier is not the consensus view!
re #96:
As a matter of principle, I admire the type of skepticism you describe. I personally tend to think the situation is rather dire, but I’m not an expert either – although I have been impressed with the scientific articles I have read on the subject in Science and Nature, I must say.
Matters of science and matters of policy are not one and the same, though. The sane person, when confronted with reasonably substantial evidence that he/she has a life-threatening illness, does not wait until a complete scientific consensus before seeking treatment.
Come on, if we applied the same risk analysis to GW as we did to, say, terrorism (e.g. the famous 1% doctrine) we’d have begun mitigating this decades ago. It is a reasonable stance, even if you are leaning towards skepticism, to support anti-GW legislation now instead of later. I don’t like political litmus tests either, but I don’t think this is an unreasonable one as such things go.
Regarding the IPCC AR4 WG1 Report and the Consensus
The best the “contrarian” organization Heartland Institute could come up with as criticism of the IPCC WG1 AR4 was a comment by RealClimate’s Eric Steig:
Al Gore Confronted by Own Scientists – ‘Confusion Between Hypothesis and Evidence’
Posted : Thu, 28 Jun 2007 21:20:00 GMT
Author : The Heartland Institute
Category : PressRelease
http://www.earthtimes.org/articles/show/news_press_release,131357.shtml
It is obvious that Eric agrees that climate change is a serious issue and a serious threat. At the same time, he wanted the report to be bulletproof so that it could be taken seriously by fellow scientists as an undistorted product of the best science available at the time. I am not sure that he was entirely happy with it, but that was the final draft and they presumably incorporated many of his suggestions.
With a document this large and with as many head-strong highly intelligent individuals that were involved, there are bound to be differences. The IPCC asked for criticism from those individuals. They got it, and in many cases (at least where what was being asked for didn’t result in the document becoming much more lengthy than it already was), they took that advice, and as a result the report was made that much stronger.
Is everyone happy every sentence and every word? Obviously not. But the consensus is there for every piece even when a minority disagrees on one point or another. And the consensus is strong. The consensus wasn’t created by the report, but highlighted by it – for the purpose of countering propaganda by special interests.
Moreover, the honesty of the process itself is highlighted by their openness and transparency in making available the criticisms which guided the final editing of the report.