How do we know CO2 is causing warming?
Posted on 8 October 2009 by John Cook
We've just perused the empirical evidence that humans are raising atmospheric CO2 levels. In earlier posts, we noted that tallying up the planet's heat content shows that our climate is accumulating heat, proof of global warming. But is there any evidence that links the two? Is there empirical data proving that increased CO2 contributes to the energy imbalance that causes global warming?
The greenhouse gas qualities of CO2 have been known for over a century. In 1861, John Tyndal published laboratory results identifying CO2 as a greenhouse gas that absorbed heat rays (longwave radiation). Since then, the absorptive qualities of CO2 have been more precisely measured and quantified by laboratory results and radiative physics theory (Herzberg 1953, Burch 1962, Burch 1970, etc).
Satellite measurements of the change in outgoing longwave radiation
So according to lab results and radiative physics, we expect that increasing atmospheric CO2 should absorb more longwave radiation as it escapes back out to space. Has this effect been observed? The paper Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997 (Harries 2001) attempts to find out. In 1970, NASA launched the IRIS satellite that measured infrared spectra between 400 cm-1 to 1600 cm-1. In 1996, the Japanese Space Agency launched the IMG satellite which recorded similar observations. Harries 2001 compared both sets of data to discern any changes in outgoing radiation over the 26 year period. The resultant change in outgoing radiation was as follows:
Figure 1: Change in spectrum from 1970 to 1996 due to trace gases. 'Brightness temperature' indicates equivalent blackbody temperature (Harries 2001).
What they found was a drop in outgoing radiation at the wavelength bands that greenhouse gases such as CO2 and methane (CH4) absorb energy. The change in outgoing radiation over CO2 bands was consistent with theoretical expectations. Thus the paper found "direct experimental evidence for a significant increase in the Earth's greenhouse effect".
This result has been confirmed by subsequent papers using the latest satellite data. Griggs 2004 compares the 1970 and 1997 spectra with additional satellite data from the NASA AIRS satellite launched in 2003. Chen 2007 extends this analysis to 2006 using data from the AURA satellite launched in 2004. Both papers found the observed differences in CO2 bands matched the expected changes based on rising CO2 levels. Thus we have empirical evidence that increased CO2 is preventing longwave radiation from escaping out to space.
Measurements of downward longwave radiation
What happens to longwave radiation that gets absorbed by greenhouse gases? The energy heats the atmosphere which in turn re-radiates longwave radiation. This re-radiated energy goes in all directions. Some of it makes its way back to the surface of the earth. Hence we expect to find increasing downward longwave radiation as CO2 levels increase.
Philipona 2004 finds that this is indeed the case - that downward longwave radiation is increasing due to an enhanced greenhouse effect. Evans 2006 takes this analysis further. By analysing high resolution spectral data, the increase in downward radiation can be quantitatively attributed to each of several anthropogenic gases. The results lead the authors to conclude that "this experimental data should effectively end the argument by skeptics that no experimental evidence exists for the connection between greenhouse gas increases in the atmosphere and global warming."
So we have multiple lines of empirical evidence for CO2 warming. Lab tests show CO2 absorbing longwave radiation. Satellite measurements confirm that less longwave radiation is escaping to space. Surface measurements detect increased longwave radiation returning back to Earth at wavelengths matching increased CO2 warming. And of course the result of this energy imbalance is the accumulation of heat over the last 40 years.
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#10 WAG, very perceptive post. I'm a non-scientist myself (I got as far as highschool chemistry), but this particular discussion has sparked an investigation into thermodynamics and even calculus(!). Thanks particularly to Tom Dayton, those are great resources! I'll add one here from the physics forum, it bears direct relevance. Some of the comments there are quite useful. Part of the problem with deniers is that they cannot grasp the interaction between macrolevel thermodynamics and microlevel thermodynamics, nor the relatively simple concept of equilibrium.
This discussion is quite interesting, but I have some basic observations that are pretty straightforward.
First, just to state the obvious, no one disagrees that Co2 absorbs heat and helps keep the earth warm. However, the fundamental argumet of AGW theory is that this trace gas (at slighly less than .04% of the atmosphere) is THE key ingredient to controlling a massively complex system such as climate. We can essentially dismiss the effects of solar variation, PDO, orbital changes, magnetic field changes, or hundreds of other variables and their interrelationships because we know for a fact that Co2 is the single most important component and it's interrelationships with other variables such as water vapor completely dominate or overshadow all other forcings. The argument is absurd on it's face. Just reading through the posts from both skeptics and proponents provides a pretty good indication of the complexities surrounding this science.
We hear that we are nearing a tipping point where we will have run away warming if we do not stop "polluting" our atmosphere with Co2. My quesion is - why didn't we have run away warming back in the Carboniferous period when Co2 levels were into the thousands of PPM as opposed to the 380 PPM today? Or for that matter in other subsequent periods when Co2 concentration was much higher than it is today? Instead, the earth went through several cooling and warming periods irrespective of the Co2 levels.
Another observation that has been addressed to some degree in this discussion is that there is a diminishing return of warming caused by Co2, meaning that there is a non-linear relationship between Co2 levels and warming. Yet, what most models seem to show is a linear relationship that is not supported by the science.
Lastly, if Co2 is so bad for our planet, why do people who own greenhouses increase Co2 levels to as much as 1000-1200 PPM? The reason is not because it causes harm, but because plants thrive in environments with higher Co2 levels.
Sorry, TP100, everything you wrote is a myth. You're on the right web site to get answers. Look at the top left of this page and click "View All Arguments."
CO2 is just one piece of the climate puzzle. However, as we're emitting so much CO2 into the atmosphere, it does happen to be a fairly large piece. We can theoretically calculate how much heat CO2 traps and taking into account all the various radiative forcings that cause warming, it is the greatest contributor:
We're not ignoring solar changes. We know the forcing from orbital changes and they're insignificant compared to the radiative forcing from CO2. The PDO has no long term effect on radiative imbalance - it's an internal variation resulting from the exchange of heat between the atmosphere and ocean.
You're right to point out that CO2 is not the only radiative forcing. It's important to keep this in mind when evaluating past periods where CO2 was higher than now. In some periods, the sun was less bright than now. In other periods, the planet had a completely different configuration with all the continents merged into a single continent so the radiation budget was much different.
Models and theory do not use a linear relationship between CO2 and global temperature - it's a logarithmic relationship. And our theoretical understanding is confirmed by empirical observations. As explained above, satellite measurements of outgoing longwave radiation and surface measurements of downward longwave radiation both find an enhanced greenhouse effect. Both are independent empirical confirmations of theoretical expectations. The way CO2 is behaving, the amount of heat it is trapping, has been quantitavely measured.
But from the phrasing of your post, I think you would still be frustrated by such a point by point approach to getting answers. So I suggest that you first read cce's The Global Warming Debate, which will tie together the threads. Then come back to this site to look for answers to specific questions.
My apologies for posting twice.
Tom Dayton - actually, I've read through the debate and I have found the AGW explanations lacking. The explanation essentially says - "we can't think of anything else that could cause the warming over the last 30 years, so it must be Co2". I am just not buying into that argument. There is a lot of information documenting that the earth is warming, and few people dispute those findings. The question is - is it really eing caused by man? While this website provides explanations, I can find equally if not better contrary explanations on skeptical websites.
Re: my mythical questions - Is it a myth that Co2 is only .04% of the atmosphere? And, is it a myth that Co2 concentrations were much higher in prior geologic times? Is it a myth that Co2 is a relatively weak greenhouse gas? Is it a myth that Co2 is a nutrient to plants and would would not survie without it?
My argument simply states that climate is massively complex, while when you boil down AGW theory to it's most basic level, it says climate is actually quite simple - if humans can control atmospheric Co2 levels, we can control climate. Nothing else matters, and that is an absurd argument. If that is an incorrect characterization of AGW theory, then why all the fuss about capping Co2 emmisions?
Response: The argument "we can't think of anything else so it must be Co2" is indeed inadequate. But that's not the argument being made. On the contrary, posted above is empirical evidence that increased CO2 has caused an enhanced greenhouse effect. Theory says more CO2 will trap more heat leading to global warming. Now we have observations that quantitatively confirm this.
Is it a myth that CO2 is a relatively weak greenhouse gas? Yes, the empirical evidence confirms the amount of extra heat trapped by CO2. The numbers have spoken. Climate is certainly complex but the principle that CO2 traps heat - and that more heat in our climate leads to warmer temperatures - is straightforward.
Anyway, this is the second time I've clarified that CO2 is not the only radiative forcing but it is the most significant source of warming. If you continue to persist with the strawman argument that we're claiming "nothing else matters", those comments will be deleted.
A couple of your points:
We don't dismiss the effects of solar variation (there has been negligible secular solar variation since the late 50's and so this has made a negligibile contribution to the very marked warming of this period; it's estimated by solar scientists that solar effects may have contributed around 0.1 oC of warming to the 20th century trend)..
J. L. Lean and D. H. Rind (2008) How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006 Geophys. Res. Lett, 35, L18701
...or PDO (a recent analysis of ocean current effects indicates that these have modulated the warming during the 20th century but have made almost zero net contribution)...
K. L. Swanson, G. Sugihara, and A. A. Tsonis (2009)Long-term natural variability and 20th century climate change. Proc. Natl. Acad. Sci. USA 106, 16120-16123
...or orbital changes (these have obviously played a major role in ice age cyles, and have had a small contribution to Holocene temperature variations, but their contrbution to the warming of the 20th century has been essentially zero)...
..or magnetic field effects (these have been studied in detail and there is no evidence that these have made an impact to warming of the last 100 years).
So we certainly don't dismiss these things (or any factors that are known to affect climate).
e.g. see Figure 2 here:
We didn't have "run away warming back in the Carboniferous period when Co2 levels were into the thousands of PPM as opposed to the 380 PPM today", because, in fact during the Carboniferous CO2 levels were generally very low (even possibly lower than today during parts of the Carboniferous and early-mid Permian). That's why the earth had some major long-lived glaciations and otherwise cold periods during the Carboniferous and early/mid Permian. During some parts of the Carboniferous when CO2 levels were a bit higher, the evidence indicates that the earth was warmer. In general there is a rather strong relationship between proxies for atmospheric CO2 concentrations and earth temperature regimes right throughout the last 500 million years.
TP100, read more carefully. See comment #13 on this thread -- CO2 is not thought to be the only thing affecting climate. Nobody is claiming a runaway (runaways require positive feedbacks, but not all positive feedbacks yield runaways).
Is there another forcing that has increased by 33% since 1750? Is there another forcing that might double over the next 100 years? Will solar forcing do that? But we can limit the amount of future forcing from CO2. That's not to say that we will "control" climate; rather it means that we can reduce the amount of anthropogenic forcing. I hope this gives you a clue as to why people tend to talk about carbon dioxide.
TP100, you wrote "The explanation essentially says - "we can't think of anything else that could cause the warming over the last 30 years, so it must be Co2".
That is one of the myths--that climatologists are merely casting about for an explanation. In fact the opposite thinking process is what got them to these conclusions: The fundamental physical causes were realized in the 1800s and very early 1900s, including the prediction that those physical mechanisms would cause global warming. That was decades before it was possible for anyone to observe global warming. Lo and behold, now that we have the ability to observe, we discover that the predictions are accurate. There are concrete, physical, experimentally verified mechanisms for the effects.
TP100, you wrote "However, the fundamental argument of AGW theory is that this trace gas (at slightly less than .04% of the atmosphere) is THE key ingredient to controlling a massively complex system such as climate. We can essentially dismiss the effects of solar variation, PDO, orbital changes, magnetic field changes, or hundreds of other variables and their interrelationships because we know for a fact that Co2 is the single most important component and it's interrelationships with other variables such as water vapor completely dominate or overshadow all other forcings.
That is another myth. It's easy to get that misimpression, though, because climatologists tend to take for granted that everybody already knows the other forcings have been accounted for. As Chris and SteveL replied to you, there are many other forcings. Attention being focused on CO2 because the other forcings have small or no long-term changes (trends) at this time. At various times in the past, various of those other forcings have changed more than CO2 has. But not now. Another reason for our focus on CO2 is that it is one forcing we can do something about.
TP100, you wrote "Is it a myth that Co2 is only .04% of the atmosphere? ... Is it a myth that Co2 is a relatively weak greenhouse gas?"
See my comment #17 to the post "How we know global warming is still happening."
TP100, you wrote "Lastly, if Co2 is so bad for our planet, why do people who own greenhouses increase Co2 levels to as much as 1000-1200 PPM? The reason is not because it causes harm, but because plants thrive in environments with higher Co2 levels." And then you wrote "Is it a myth that Co2 is a nutrient to plants and would would not survie without it?"
Nobody is making that broad claim that CO2 is "bad for our planet." Instead there are claims about several specific effects of the warming and ocean acidification caused by extra CO2--CO2 beyond what we have now. The effects of CO2 itself on plants are some positive and many negative. For example, some weeds such as poison ivy will thrive with greater CO2--more so than many other plants--but we don't really want weeds to thrive. And plants do not just grow better with higher levels of CO2. They grow differently. For example, some put more of their materials into inedible stalks than into their fruits, making crops harder to process without a concomitant benefit.
There is a U.S. Department of Agriculture report with handy fact sheets on the effects of global warming and higher levels of CO2, and the news definitely is not all good.
Also see the comments starting with comment #9 on the Skeptical Science post "Are humans too insignificant to affect global climate."
TP100, regarding the overall benefits of more CO2, see the Skeptical Science post Global warming is good.
@ J Cook
“I'm surprised to hear you say global temperature has risen as fast numerous times over the last few thousand years”.
here the graph of Moberg and Esper without instrumental data
so that "apples and oranges" are not compared
Response: Pielke isn't disputing the results of Philipona 2004 - I suggest you read the post you link to.
I don't see the point with the Pielke references, as Evans & Puckrin (2006, link is given above just after the Philipona paper) show that the change in DLR reported by Philipona et al. is caused by greenhouse gases.
There is one thing that bothers me about figure 1 (the differential spectrum). The decreased emission in certain absorption bands makes perfect sense. But it's a fact of the (surface) instrumental record that the planet was (a little) warmer in 1996 than in 1970 (somewhere in the 0.1 to 0.2C range). So shouldn't the flat parts of the differential spectrum be just a bit above zero?
I like your explanation but this study did not look at the cooling and weigh the warming and cooling effect of carbon dioxide against one another. Check this http://www.globalwarmingart.com/images/7/7c/Atmospheric_Transmission.png
Note that some 30% of the sun's radiation is "absorbed" in the atmosphere, by ozone, oxygen, water and carbon dioxide. Most scientists think that this difference is what heats the atmosphere. I will admit that the aborption of photons may cause some heating but there is a limit to the number of photons that can be absorbed by a substance. The radiation is then re-emitted. I believe the larger amount of this 30% is re-emitted (the same principle as the greenhouse effect) and a large portin is reflected out from the atmosphere back into space. Did anybody of you ever thought of measuring the cooling effect of carbon dioxide?
I want to know the nett effect.
Henry pool, from the way you wprd it, I can't be sure, but I believe that what you're describing is mainly seen in the stratosphere. I recall that the Iacono and Clough (1995) paper is considered a seminal paper on the subject.
I still have some questions regarding you response to TP100
[ Response: Theory says more CO2 will trap more heat leading to global warming. Now we have observations that quantitatively confirm this.
I think you have done a good job of this, but I haven't seen solid indication of the magnitude of impact (how much temperature increase can we expect with the next incremental increase in ppm concentration.) This is important to the debate, because policy is being decided based on very "scary" scenarios that this magnitude is great, but I haven't seen any science on this.
you made the comment "but for one theory to supplant another, it must explain/predict more than the incumbent theory."
This is true, however usually theory's have a basic ability to predict. I have seen much with regards to the correlation between Temperature and CO2, but the predictions on how temperature will change with increasing CO2 concentrations have been horribly in accurate. So, until the temperature / co2 models get some degree of credibility, it's difficult to accept the premises that CO2 is the culprit for the increase in temps.
"This statement by Truth Seeker: "I have found the UN to be a horribly corrupt organization" is totally meaningless and bad rethoric ... How relevant is it?"
It is relevant in that I don't accept IPCC (UN) as being an organization of Scientist, rather they are a political organization (and a relatively corrupt one at that) with policy agenda. Their call for action has my highest suspicions, and I look to real science (done outside of this organization) for evidence of the truth.
The thing I like about this site is that most of the arguments and evidence I find here meet that qualification.
TS, all the science used by the IPCC is done "outside" of the organization. You say you like the science papers presented in this site. Did it occur to you that most of them are part of the body of science used by the IPCC in its work?
It appears no one ever seemed to have come up with the thought that carbon dioxide also causes cooling.
If you read the IPCC reports, you'll see they're basically just a summary of all the peer reviewed scientific literature. It reads like a science textbook (a rather dry one) and its conclusions are conservative. I often use the AR4 as a starting point to lead me to what papers are out there. I strongly recommend reading the IPCC Fourth Assessment Report
- you will learn a lot about all the research that's out there.
I did not receive an answer to my question at post 67.perhaps I still get an answer. But I doubt it. It seems everyone forgot to look at the cooling aspect.
In my view, especially with CO2, the way for radiation from the top to the bottom is the same as for the bottom to the top because the CO2 is almost 100%diffused into the air, so this question is and must be relevant. Why did no one ask it before? The cooling does not happen just in the upper air, it happens anywhere.
I am busy carefully analyzing the graphs that I posted at 67, and all in all, it looks to me pretty much evens up,
In other words: the cooling effect might in fact be just as much as the warming effect.
If you enlarge it big enough you will notice that there are a few small gaps caused in the sun’s radiation
which is due in part to the two absorptions of carbon dioxide between 2 and 3 um.
It seems to me that the spectral intensity at the 4-5 um absorption is pretty much the same for both the sun and earth,
although it is probably not on the same scale. But let us say this cancels each other out, more or less.
It seems there is a small corner of radiation not being emitted by earth due to the CO2 absorption, at 14 um.
(note that water is also absorbing here). This is the warming effect.
Without someone doing some experimental testing, I think it will be difficult to quantify which is the biggest: the cooling or the warming.
But if you ask me, it looks to me that the nett effect is or will be close to zero
Co2 is not CO2.
Co2 is molecular cobalt (Co). Why didn't the moderator pick up on that?
I'm a little bit confused by what you call the cooling effect of CO2. Do you refer to the part of the radiation that is re-emitted toward space after absorption?
If this is what you mean, the point is that the process of absorption and re-emission happens through the whole atmosphere, true, but at very different temperatures and pressures going from the surface up.
At some point (altitude), the radiation will escape to space and it's the temperature and pressure at this point that matters for the energy balance.
Yes, I am talking about the the radiation from the sun hitting on the carbon dioxide. A large portion of that radiation must be scattered away to outer space. You can observe same effect if you stand in the sun (here in Africa) - you will notice that the heat coming directly at you from the sun definitely decreases as the humidity increases. You can feel it. So, the same observation must be true for carbon dioxide. At all levels of the atmosphere. Notice (from the graphs) that at quite a few points the water vapor and carbon dioxide work together to keep us cool.
I don't understand how we can go to Copenhagen with this and nobody studied what the nett effect is of the cooling and warming caused by the carbon dioxide. How do we know for sure that the warming effect is bigger if nobody did some experimentation on this?
I don't think that temperature and pressure (have to)come into this at all? The CO2 is diffused in the air, therefore you can see it behaves the same as does oxygen.It keeps us cool (during daytime, 12 hours per day) and it keeps us a bit warmer (all of the time) but what is the nett effect?
my reasoning was upside down, the IR radiation leaving the earth surface. Instead, you're are talking about scattering of visible light from the sun, a completely different issue.
No problem about Copenhagen, we can go safely. Scattering is a old and well known phenomenon. The intensity of the scattered light depends on the size of the partiicle and CO2 is quite small; on the contrary, water vapour tends to form liquid droplets (or ice crystals) which are several order of magnitude bigger than a single molecule. Hence droplets suspended in air scatter incoming sunlight much more efficiently than CO2 molecules, the latter being negligible.
As a take away message, don't think scientists (and i'm not one of them) are not smart enough to account for the known physics.
Yes Riccardo!- I am glad you understand. I am talking about both directions. The cooling is coming from the top to the bottom, the warming is going from the bottom to the top, or rather, from the bottom up back to the bottom - i.e. the greenhouse effect!! Your argument that carbon dioxide is a "small particle" surely applies both ways. i.e. both for earth and the sun. I therefore would like to see the actual figures or measurements from experiments -do you have them? What is the nett result of the cooling and the warming effect of CO2??
you have to consider the different wavelength range in the two cases.
In the visible range (sunlight coming in) the CO2 effect is definitely negligible, there's no significant absorption nor scattering. No cooling, as you call it.
As for the radiation coming from the earth surface (infrared going out), there's no significant scattering as well but there's absorption (at certain characteristic frequencies). Again, no cooling.
More generally, as in the case of aerosol, you can have a net cooling effect due to the combined effect of absorption and scattering. But this is a much more complicated matter and infact is the biggest single contribution to the uncertainty in the estimates of the total net forcing.
Hi Riccardo, I refer to my post 73. Please read this first. It seems there is a general misconception about the term absorption. Absorption is a term that came from spectroscopy. What happens is that that at these wavelengths where absorption occurs, one or two photons are accepted. What then happens (at these wavelengths)is that the molecule turns into a mirror and the rest of that radiation (at these wavelengths)is then re-emitted. Because of the random position of the molecules you may assume 50% beamed back to earth or back to space, depending on where the radiation came from in the first place. Now there is a limited amount of carbon dioxide (i.e. ca. 350 ppm) in the air, so it not possible for that much "energy" to be taken up before it starts re-radiating. See the definition of the greenhouse effect in Wikipedia. This may be unlike the oceans and the seas. There is virtually an unlimited amount of salts that may be able to accept photons. And on a macro scale humans are busy taking water from the oceans (rain), collecting it in dams and using it up for irrigation and consumption.. What flows back into the seas might even have more salt than the oceans.....
the lifetime of the excited state is very short, expecially at high temperature and pressure. There is no significant "mirror effect" (sic) at all.
What is true, instead, is that the photon might be re-emitted at the same wavelength, but it's too simplistic to assume that it's irradiated back to space. You need to consider the atmosphere as a whole so the chances that the photon gets re-absorbed are high near the ground and progressively reduce going up. And here comes the concept of which i wrote a few comments back; it's the altitude at which the photons might actually escape to space that matters for the energy balance.
You might want to read a little bit more on this in a standard climate textbook (e.g. Principles of Planetary Climate available online).
Be sure that there's lot people around able to take all of this into account ;)
Quote from Wikipedia (on the interpretation of the greenhouse effect);
"The Earth's surface and the clouds absorb visible and invisible radiation from the sun and re-emit much of the energy as infrared back to the atmosphere. Certain substances in the atmosphere, chiefly cloud droplets and water vapor, but also carbon dioxide, methane, nitrous oxide, sulfur hexafluoride, and chlorofluorocarbons, absorb this infrared, and re-radiate it in all directions including back to Earth."
Because of the random position of the molecules we may assume that at least 50% of the infra red from earth is radiated back to earth. The process repeats itself.
Did you have a close look at the graphs (web link) that I posted in 67? You can clearly see that the greenhouse efect is relevant for carbon dioxide at about 14 um. But water absorbs there as well.
But note that there is also an anti greenhouse effect - especially at between 2-3 um and between 4-5 um where we still have the sun's radiation. Interestingly at between 4-5 we also have some radiation from earth.So it looks to me these two cancel each other out.
But it seems you still do not understand. For example: Look at the absorbtion of oxygen and ozone at 10 um. At this wavelength there is no absorption coming from either the water or carbon dioxide. Can you see that this absorption at 10 causes a dent in the radiation coming out from earth? You can say the ozone/oxygen is "blocking" (mirror?) some of the radiation going out from earth at 10. That is why even oxygen and ozone are greenhouse gases. But now for you to say to me that the radiation from the sun that is being "blocked" by carbon dioxide is irrelevant surely is the same as saying that the greenhouse effect is irrelevant? Both are relevant. But what is the nett effect? Is the cooling more or is the carbon dioxide warming more?
I am not interested in what a lot of people are saying or thinking. I am only interested in what I can see is happening. Please try to understand my thinking here and make a big print-out of that weblink that I gave in 67, I am sure you will begin to understand what I am saying when you follow the example that I gave with the gap in the radiation from earth at 10 um caused by the oxygen and ozone absorption at 10.....
Henry Pool, regarding the net of reflection and absorption, try reading cce's section 1, Primer and History. Take special note of the third figure. If you want to dig deeper, look at the references listed for those figures.
your terminology definitely confuses me. I can not understand what an anti-greenhouse effect is nor what you mean by "blocking" or absorption or "mirror".
Also some concepts appear to be messed up. You say "But now for you to say to me that the radiation from the sun that is being "blocked" by carbon dioxide is irrelevant surely is the same as saying that the greenhouse effect is irrelevant?"
Can you see any difference between the light coming from the sun and the radiation coming from the earth surface and atmosphere?
Also reflection, scattering and absorption appear to be used out of context. Probably following Tom Dayton advice is the best you can do.
Thanks to all for this blog. I am grateful for finding it, in that it appears to be able to accommodate dissenting views without immediately resorting to abuse and non-sequiturs.
I read the series of Haries papers, and have a serious question about the interpretation of the results. I should first of all offer my congratulations to the succession of authors who have heroically tried to reconcile and calibrate three different datsets into a meaningful composite comparison.
My question is this: if it is CO2 causing the warming why would one expect a signature that shows a dip in OLW flux at peak CO2 frequency and an overall reduction in the MODTRANS integral of emissions?
My understanding of the theory of AGW was that increasing CO2 should slow down emission at the principal frequencies of CO2 and increase the temperature at TOA to bring the radiative balance back into equilibrium. This suggests that the integral should be about greater over the period measured after 27 years of temperature increase, rather than reduced as the graph implies. It further suggests to me that the radiation at CO2 principal frequencies should be increased rather than reduced, since under the "saturated gassy argument" we should have more CO2 in the upper stratosphere - implying greater emission at the principal frequencies. Can anyone clear up my confusion here?
On a separate point, it seems to me that we should now have several years of high quality satelite data across a broad frequency band. Why have we not yet seen a "3D picture" showing 2-D waveband vs time and temperature. This would surely help to close the conversation one way or the other?
I'll give my take assuming i understood your question correctly.
You should consider the background (the parts of the spectrum where there is no absorpion) and the absorption peaks separately. Indeed, they are due to different processes: the former is an emission process and is related (among other things) to temperature, the latter is an absorption process and is related to CO2 concentration.
As for the background, it is a blackbody-like emission and is contaminated by various effects (listed in the paper). In principle, it is expected to increase with warming, as you correctly say.
As for the peaks, you expect more absorption as CO2 concentration increases (roughly independent on temperature for small increases) and then a reduction of the intensity reaching the detector. Here, instead, you apparently think in term of emission as well and then expect an increase.
OK, Let us take Tom's paper "(The Global warming debate") and work it through backwards to front.
pages: 10-13: there is no doubt that global warming is happening. I do not doubt it.
Page 9: ice core analysis:Al Gore and them apparently analysed ice cores going back to as far as 650000 years. Then they said, and I quote (from the movie): " whenever the carbon dioxide was higher the climate was warmer." So I asked myself: but why were there periods in history (before man and any kind of major human activities) when the carbon dioxide was higher? Well, where does all carbon dioxide come from? It comes from volcanic activities! That is why life came into existence. Water and carbon dioxide are like our father and mother. So when there is more volcanic activity, should we not expect a temperature rise? There is an awful amount of heat released when volcanoes explode. So that explains that correlation.
Page 7: Why always measure carbon dioxide at Mauna Loa - so nearby an active volcano? Are there no other places? The graph does not have 0 ppm on, so it gives a bit of an extra slope upwards that should not be there.
Page 6: Almost 100 years ago, Svante Arrhenius predicted that carbon dioxide in the atmosphere would cause warming up. In the meantime, carbon dioxide has increased even more than he expected, but the Earth hasn't warmed as much as he thought it would (applying his formula). Why did no one check his eperiments with modern day equipment? Anyway, it appears to me that subsequent followers have always assumed that his theory must have some truth in it. Eventually, the whole theory really became something like this: let us have a planet, add more carbon dioxide, see if the temperature goes up, it did, so that must be it! I also studied the IPCC report. It seems to me what they did in the IPCC report is to compare the concentrations of the gases in 2005 with 1750. Then they assigned a measure of relative radiative forcing to the so-called greenhouse gasses depending on the increase in concentrations measured. But this is like working at the problem from the wrong end! That is assuming that you are 100% sure what the cause is (of global warming) and then trying to work your way backwards to find a solution to the problem. They took all the gases that absorb infra red as positive forcing. "This must be the cause, what else can it be?"
Page 5: The beaver story can apply to other possible causes - I touched on one possible other cause for global warming in my post at 80.
Page 3-4: The graphs are familiar, they are the same ones that I have been referring you to before. Do place these two graphs on top of one another. Now for example: Look at the absorption of oxygen and ozone at 10 um. At this wavelength there is no absorption coming from either the water or carbon dioxide. Can you see that this absorption at 10 causes a dent in the radiation at 10 coming out from earth? So here is how best to describe the greenhouse effect:Where we have absorption the molecule can except one or two photons from the radiation (and it gets a little warmer), but once this transaction is completed the molecule at that frequency becomes sort of like a mirror: it blocks any further radiation forcing it backwards to where it came from. It cannot allow the radiation to pass through anymore. Don't make it more difficult or confusing than what it is.
Page 2: the solar Radiation graph is very important. I have a slightly better one that goes a bit into more detail.
The explanation given on page 2 is very poor. Let me re-write this a bit: The top of the yellow is the radiation what has been measured above the atmosphere (it follows a lobsided curve). The top of the red is what was measured at sea level on a clear day. The difference (=yellow surface area) is the radiation that was either absorbed (i.e. turned into heat), reflected (or 'blocked") or scattered by the atmosphere before reaching the surface of earth. The gaps (= yellow surface area - I refer to this as cooling or the anti greenhouse effect) are caused by the combined efforts of ozone, oxygen, water and carbon dioxide. So the same gases that cause the greenhouse effect are also causing the cooling (or anti greenhouse) effect. Without it, even more radiation from the sun would be slammed into heads and into our oceans. Note that the absorption of a molecule at a certain wavelength does not have to be strong to cause a blocking or "mirror" effect.The width is important.
So now let us look at the absorptions of carbon dioxide together:
We have the first absorption at 1.4um.It shows a blocking effect (= yellow surface) on my graph.
We have a 2nd absorption at 1.7 or 1.8 um. It shows a blocking effect (= yellow surface) on my graph.
We have another absorption at around 2 um. It shows a yellow area being caused in my graph and your graph of page 2.
We have another absorption of carbon dioxide at just before 3 - it shows a cooling effect (i.e. yellow surface area) on my graph
We have strong absorption between 4 and 5 um. It falls of the scale on both (solar radiation) graphs, but we know that between 4 and 5 um there is still about 0.5% radiation coming from the sun (according to my table).
We now go to warming (greenhouse effect)
We have strong absorption between 4 and 5 um.
It appears that a little bit of earth's radiation is being blocked by this but the spectral intensity of earth is still low between 4 and 5.
There is strong absorption at 14-15. It leads to some of earth's radiation not being emitted. Note that oxygen also has a very weak band here and water also absorbs here. These 2 gases have much higher concentrations than carbon dioxide so it is difficult to see or know exactly what the influence of the carbon dioxide on its own.
So my question to all the scientists who worked on this problem is still the same: what is nett effect? How were the tests done to determine that the warming effect of carbon dioxide is greater than its cooling effect? Where are those figures?
PS: Sorry Tom, I did not understand you here: "Take special note of the third figure" - what figure were you referring to? I did not see anything in this paper like that.
you jumped off science all in a while; indeed, you're inventing a new one. I stick on the good old one and there's no answer I can give you.
But i don't want to be told that i do not motivate what i say, i'll give you a few example. Just a few, going through all of them is not worth the effort.
Page 9: correlation between volcanoes emissions and glacial cycles. Blatantly false, look at the numbers of CO2 emission from volcanoes; and also at how the earth orbit works.
Page 7: CO2 measured only at Mauna Loa. Ridiculous, there are stations all over the world. Ad the slope of a curve is its first derivative whatever the axis you choose, it's just a metter of showing or hiding something.
Page 6: the very same Arrhenius experiment has been performed countless times. We now know the abosrption coefficient with great precision over several order of magnitudes.
Page 3-4: the picture you give of the basics of spectroscopy (you used this word) are naive. Two photon processes, "act like a mirror", come on ... i'm making it as difficult as it is in any standard undergraduate textbook.
And so on, and on, and on ...
But I can answer to the simple question "what is the net effect?": no matter which freak processes you immagine are at play, it's warming, no doubt.
Henry Pool, I linked specifically to section 1, Primer and History. In that section, the third figure from the top is a greatly simplified diagram of incoming and outgoing energy.
Regarding your comment 87:
"Page 9": Al Gore did not analyze ice cores. Al Gore is not a scientist. He just does a good job of educating people about scientists' research.
So when there is more volcanic activity, should we not expect a temperature rise? There is an awful amount of heat released when volcanoes explode. So that explains that correlation.
No, it doesn't; see the "Skeptic Argument" list at the top of this page you are reading right now? That's where you'll find a response to the argument It’s volcanoes (or lack thereof).
Page 7: Why always measure carbon dioxide at Mauna Loa - so nearby an active volcano? Are there no other places? The graph does not have 0 ppm on, so it gives a bit of an extra slope upwards that should not be there.
In fact, CO2 is measured in lots of other places; one list of the locations and ways of measuring is at the web site of the Carbon Dioxide Information Analysis Center at Oak Ridge National Laboratory. Mauna Loa is the most frequently listed when a short, simple explanation is the goal, because it is one of the most pristine and continuously measured sites, and its values well match the average of all the other sites. As for the graph's lack of a 0, in fact that is completely inconsequential--literally, inconsequential--with regard to the slope. Maybe you're confused because you think what matters is how sloped the line looks to the human eye. But in fact the visual appearance is irrelevant, because the statistics describing the line are what are actually used.
Page 6: Almost 100 years ago, Svante Arrhenius predicted that carbon dioxide in the atmosphere would cause warming up. In the meantime, carbon dioxide has increased even more than he expected, but the Earth hasn't warmed as much as he thought it would (applying his formula). Why did no one check his eperiments with modern day equipment?
It seems you are not really reading the material, but only skimming very superficially. This very page you are reading right now is filled with exactly that modern, empirical, evidence. Maybe what you're wanting is something like The Carbon Dioxide Greenhouse Effect section of Spencer Weart's history of The Discovery of Global Warming.
It seems to me what they did in the IPCC report is to compare the concentrations of the gases in 2005 with 1750. Then they assigned a measure of relative radiative forcing to the so-called greenhouse gasses depending on the increase in concentrations measured. But this is like working at the problem from the wrong end! That is assuming that you are 100% sure what the cause is (of global warming) and then trying to work your way backwards to find a solution to the problem. They took all the gases that absorb infra red as positive forcing. "This must be the cause, what else can it be?"
No. That's what this entire post by John Cook is about. Read it again. Click on the links he provides to his earlier posts. Don't just skim.
So here is how best to describe the greenhouse effect:Where we have absorption the molecule can except one or two photons from the radiation (and it gets a little warmer), but once this transaction is completed the molecule at that frequency becomes sort of like a mirror: it blocks any further radiation forcing it backwards to where it came from. It cannot allow the radiation to pass through anymore. Don't make it more difficult or confusing than what it is.
You are incorrect. It does not block futher radiation. It is not in any way like a mirror. That's just not how it works. Really. See The CO2 effect is saturated. If you want a detailed explanation, start with A Saturated Gassy Argument and then read its Part II: What Angstrom Didn't Know.
So my question to all the scientists who worked on this problem is still the same: what is nett effect? How were the tests done to determine that the warming effect of carbon dioxide is greater than its cooling effect? Where are those figures?
The answers to those questions have been right in front of you all along. That's what all these web sites describe. The empirical measurements described in John Cook's article at the top of this very same page you are reading right now, have been used to find the net effect. The diagrams of the Earth's incoming and outgoing energy show exactly those factors, with the resulting net effect--the Earth's "energy balance." (A more detailed diagram is in the IPCC's FAQ 1.1. See the Skeptical Science article Measuring Earth's Energy Imbalance.
Thanks Tom! I will study all this and get back to you.
You wrote"You should consider the background (the parts of the spectrum where there is no absorpion) and the absorption peaks separately. Indeed, they are due to different processes: the former is an emission process and is related (among other things) to temperature, the latter is an absorption process and is related to CO2 concentration."
Thanks for this. I am in learning mode. If I consider a very simple model of completely constant solar irradiation, an Earth in radiative balance with constant albedo, and I perturb the system by throwing in additional CO2 and then allow the system to re-establish radiative equilibrium, then I would expect that integrating across the resulting TOA emission spectrum to obtain total outgoing flux should yield by definition a value equal to the (constant) incoming solar flux. If one finds a dip in flux at the principal frequencies of CO2, then it must be compensated by an increase in other parts of the spectrum for the integral to balance. The Harries papers appear to show a net reduction in flux over the bandwidths examined and a large dip at the absorption frequencies of CO2 and methane (author's comments on the problem noted).
My confusion is arising in part because I would not automatically expect to see a dip in TOA emissions at the CO2 frequencies. (The increased path length should slow down radiative transfer at those frequencies, but yield the same number of photons and the same net flux at top of atmosphere (TOA). I would expect the flux to be the same or even marginally higher because of the increased emissive presence of CO2 in the drier upper atmosphere (Kirchoff?). My question can then be summarised as follows: if there is in reality a net loss of flux at the CO2 frequencies at TOA, where do you expect to see the compensating gains in the rest of the spectrum and WHY?
Tom, let me take it from the top now, & don't get mad at me if I don't agree, OK?:
I agree with the third picture. But A (= reflected by the atmosphere), for a large part means the green house gasses working to keep us cooler, yes? Are we agreed on that? Do you see that the cooling comes with the warming? Did you see that the info they give on page 2 is terribly confusing? But they warn you not to worry about that because the graph is "not important". Can you honestly say that that is good science? To me, it seemed they want to hide the cooling effect.
As far as volcanic activity is concerned: it is mostly in the oceans. The mid atlantic ridge is one big volcano. In the pacific we exploded all these atomic bombs. Hence all these earth quakes and tsunamis? Who knows. So, really, we dont know exactly how much volcanic activity is going on down there, nobody really knows how many kilojoules of energy are leaking into the oceans. Go watch Iceland or Hawaii if you want to get an impression, because these are 2 places with volcanic activity that stick out, the rest is deep down below under water, going all around the earth. 70% of earth is ocean and most volcanic activity is there. If there are scientists who claim to know how much energy goes into the oceans from that activity they must be speculating, yes?
So the correlation with warmer weather could be there. It is not impossible. Those eruptions on land that caused cooling are not the majority - most volcanic activity is in fact far beneath the surface of the oceans. Ask any expert.
Ok, to me, because Mauna Loa is nearby a volcano, I thought it is perhaps not the best place to measure CO2. I did not see any other graphs. But I will accept your word for it that the other places show the same results. As far as the graph is concerned: true, it does not change the results. What irritated me was Al Gore and them arranging the two graphs of the CO2 increase and the global warming increase in such a way that it looks the same. Like that,I can also prove anything that I want to prove.
The current paper shows increase in down going longwave radiation. This again may have a number of causes - whatever it is that is causing more heat on earth.. For all I know it could be aeroplanes or rockets or whatever. I donot know yet. I still have an open mind. But the point is: we know that global warming is happening. That is not under dispute. What I doubt is that the carbon dioxide is the cause. On balance, I think CO2 causes as much cooling as it does warming. And I have not seen any definitive proof of results of testing where a comparison was made in a balance sheet..
I can quote at least two people who agree with my interpretation (of the greenhouse effect) and I am stunned that you do not see it this way. Are you saying that the quote in Wikipedia is wrong? (see my posting in 82)
I will check those references you gave later.
Maybe John Cook can tell me where to look to see the answer to my simple question, (about the nett effect)
As this is just my hobby, I don't have that much free time.I do not see the answer in those references, there are just too many variables.
We only need to know: what is the cooling effect of CO2 and what is warming effect? Other stuff is not relevant. That is why I chose to blog in this subject: How do we know for sure the problem of global warming is caused by carbon dioxide?
I am not convinced yet. But maybe I want to keep things simple, so that I can still understand it? But if I cannot understand it, how can government officials (who have no chemical back round) make the right choices?
"if there is in reality a net loss of flux at the CO2 frequencies at TOA, where do you expect to see the compensating gains in the rest of the spectrum and WHY?"
You are basically correct. One should indeed expect a reduction at the CO2 absorption wavelength, not more emission. To simplify the picture, think at the measured spectrum as the thermal emission from the earth minus the absorption of the atmosphere, hence more absorption means less radiation intesity loss to space. The real process is a bit more complicated because you cannot separate absorption and emission (Kirchhoff, indeed) and one needs to consider what happens layer by layer (what is emitted upward is again in part abosrbed by the layer above, and so on); nevertheless, the general idea is still correct.
If you let your immaginary earth reach equilibrium, the fluxes need to be in balance, as you correctly say. What is missing at the CO2 wavelength will appear as background because the earth is warmer than before. You don't see the effect in Harris paper because of some factors affecting the measurement system and other related to the real atmosphere.
Henry Pool, you wrote that the IPCC "took all the gases that absorb infra red as positive forcing. 'This must be the cause, what else can it be?'" No, they did not. See the new Skeptical Science post CO2 is not the only driver of climate.
Thanks again. My model (or more likely my understanding of the model you present) is taking me to several paradoxes. If we continue to examine the mental model of a grossly simplified imaginary earth, we can consider emission at TOA, rather than from surface of the Earth. If the imaginary Earth does indeed act like a black body emitter, then the temperature at TOA should be exactly the same as before more CO2 was added (Stefan-Boltzman), since the total flux, we agree, has to be exactly equal to our conveniently constant solar flux. (The adjustment would be in the lapse rate and the height of TOA.) Since there is no physical mechanism to "order" the increased CO2 to cease or decrease transmission at the TOA temperature, am I correct in assuming that you are asserting that even our imaginary Earth cannot be treated as a black-body transmitter and Stefan-Boltzman is not applicable - even in the simple zero dimension calculations used to estimate the effect of a GH forcing?
Secondly, if the expectation of a fall in net flux at the CO2 principle frequencies is correct, then that implies a continuous process of loss of energy over time in those bandwidths to other bandwidths. While some switch to overlapping vibrational frequencies of other atmospheric components via photon transfer seems to be perfectly plausible, the remaining continuing energy loss from these wavelengths would have to be in the form of kinetic thermalisation from the CO2 to other non-dipolar molecules. No? And if this is the case, then that implies a "bottom-up" heating effect along the lines proposed by Heinz Hug. It would also imply a very small sensitivity of temperature to CO2 (since most of this energy loss would take place close to the ground and be overwhelmed by convective forces). I think I retained a copy of a Kiel and Trenberth paper on radiative calculations. I will go back and check, but from memory, the calculation is based on a layer by layer radiative transfer and flux adjustment against a fixed vertical clear-skies temperature profile - no kinetic thermalisation allowed. Where am I going wrong here?
Henry Pool, you wrote:
Because Mauna Loa is nearby a volcano, I thought it is perhaps not the best place to measure CO2. I did not see any other graphs. But I will accept your word for it that the other places show the same results.
The Scripps Institution of Oceanography's FAQ Isn't the Mauna Loa record influenced by CO2 emitted by the volcano? answers:
If one looks at the minute-by-minute data from Mauna Loa, one finds rare occasions when the CO2 is elevated from emissions from fumaroles upwind on the mountain. The fumaroles are emitting constantly, so the timing of the events depends on wind direction and not changes in volcanic activity. These events impact only a tiny faction of the data and are easily distinguished from rest of the record. The reported version of the Mauna Loa record has been “filtered” to remove these events, as well as other certain other local effects, as described in the early publications (see Keeling 1960 Tellus paper.)
For more details, see NOAA's How we measure background CO2 levels on Mauna Loa.
You don't have to accept my word that CO2 measurements are globally consistent. "The Global Monitoring Division of NOAA/Earth System Research Laboratory has measured carbon dioxide and other greenhouse gases for several decades at a globally distributed network of air sampling sites (Conway, 1994)." They publish a graph of those measurements under a graph of the Mauna Loa measurements, so you can compare them for yourself. Scroll down that page to the section "Trends in Atmospheric Carbon Dioxide - Global".
Nor is NOAA the only organization that measures CO2; see a compilation of data from organizations based all around the world, at the World Data Centre for Greenhouse Gases.
Further to the above, I was right that Kiel and Trenberth do not account for loss of radiative intensity via kinetic thermalisation, but I did note from one of their presentation diagrams in a 1997 presentation that they too seem to expect that an increase in CO2 will lead to a reduction in net OLW round the CO2 principal frequencies. Still puzzled.
Henry Pool, you wrote in #93:
...nobody really knows how many kilojoules of energy are leaking into the oceans.... If there are scientists who claim to know how much energy goes into the oceans from that activity they must be speculating, yes? So the correlation with warmer weather could be there.... Ask any expert.
The experts are not speculating. They actually measure.
A summary is in section 17.4.1, Global heat flow, of Mussett & Khan's Looking into the Earth: An Introduction to Geological Geophysics (2000, Alan E. Mussett & M. Aftab Khan, page 279, free online partial preview).
71% of the Earth interior's heat loss is from ocean-covered surface; you can see a breakdown in section 7.4, Worldwide heat flow: total heat loss from Earth, especially Table 7.3 on page 286, of Fowler's The Solid Earth: An Introduction to Global Geophysics (2nd Edition, 2005, C.M.R. Fowler, free online partial preview). An even more detailed breakdown, even across types of undersea crust, is in Pollack, Hurter, & Johnson (1993, Heat Flow from the Earth's Interior: Analysis of the Global Data Set, Reviews of Geophysics, Vol. 31(3), pages 267-280, full text available for free). A more recent source that is just as technical as the 1993 Pollack, Hurter, and Johnson article is the 2005 book chapter by Jaupart and Mareschal, Constraints on Crustal Heat Production from Heat Flow Data (in R.L. Rudnick (Ed.), The Crust, pages 65-84, free online partial preview).
A summary of how the experts calculate the heat flow from the crust that is covered by oceans are in that same Fowler book, section 7.5, Oceanic Heat Flow, starting on page 288 (free online partial preview). Details are in that same 1993 Pollack, Hurter, & Johnson article (full text available for free) and that same the 2005 book chapter by Jaupart and Mareschal (free online partial preview).
Those experts say that the total heat from the Earth's interior arriving at the Earth's surface (covered by land plus covered by sea) is about 0.09 watts coming out of each square meter from the Earth's interior. That's about 10,000 time less than the energy from the Sun (1,370 watts/m^2 on the sunlit side). That is such an inconsequential amount that any changes in it since 1850 cannot possibly have any significant effects on global temperature, compared to the other forcings such greenhouse gases and even solar variability. Furthermore, the observations of heat loss from the Earth's interior have not revealed any significant changes in the time frame of anthropocentric global warming.
So heat emission from the Earth's interior simply is not a player in the era of anthropocentric global warming.
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