Simple observational proof of greenhouse effect
Posted by Ari Jokimäki on March 10, 2010
I have seen people claiming that warmer world and more carbon dioxide is better because who wouldn’t like warmth and carbon dioxide is such a life gas (despite of the science).
I have seen people claiming that climate sensitivity is lower than thought so even if carbon dioxide has caused some warming, it won’t cause catastrophic warming (despite of the science).
I have seen people claiming that it’s not carbon dioxide that is causing warming so any actions on carbon dioxide emissions are useless (despite of the science).
I have seen people claiming that there has actually been no global warming at all but it’s just UHI and Hansen & Jones doing tricks on the temperature records (despite of the science).
I even have seen people claiming that the greenhouse effect does not exist…
The last one of these claims is why I’m writing this thing now.
The observations
Ellingson & Wiscombe (1996) gave a description of the Spectral Radiance Experiment (SPECTRE) and some initial results of the measurements. SPECTRE is a surface-based experimental field program which has a goal to “…establish a reference standard against which to compare models and also to drastically reduce the uncertainties in humidity, aerosol, etc., which radiation modelers had invoked in the past to excuse disagreements with observations.”
They are measuring the atmospheric longwave emission, i.e. the thermal radiation that atmosphere emits and which then arrives to the Earth’s surface. More specifically, they are measuring the spectrum of that emission. This is where it gets interesting. From the spectrum of thermal radiation it is possible to detect the influences of different greenhouse gases. If carbon dioxide sends thermal radiation, it has certain frequencies characteristic to carbon dioxide and as spectrum shows the emission strength at different frequencies, the spectrum shows directly if carbon dioxide is emitting thermal radiation.
In the greenhouse effect, the sunlight warms the surface of the Earth and then warm surface emits thermal radiation to the space. In atmosphere, however, there are greenhouse gases which absorb some of the emitted thermal radiation at certain frequencies (spectral bands) and then send some of it back at same spectral bands to the surface of the Earth. So, if there is a greenhouse effect caused by carbon dioxide, we should see atmosphere emitting thermal radiation at carbon dioxide’s spectral bands.
Ellingson & Wiscombe (1996) show examples of the measurements they have made. One of them is presented in Figure 1 (Fig. 3 of Ellingson & Wiscombe, 1996). There we can see at which frequencies atmosphere is emitting thermal radiation to the surface of the Earth. The effects of different greenhouse gases have been marked (CO2 is carbon dioxide, H2O is water vapor, O3 is ozone, CH4 is methane, N2O is nitrous oxide).
Figure 1. The figure 3 of Ellingson & Wiscombe (1996) showing one of their measurements of downward longwave radiation coming from atmosphere to the surface of the Earth. Measurements were made in Wisconsin, December 1991.
Conclusion
All we need to do is to take a peek at the Fig. 1 to see if greenhouse effect exists or not. See the effects of different greenhouse gases there? That’s the greenhouse effect.
References
Ellingson & Wiscombe (1996), Bulletin of the American Meteorological Society, Volume 77, Issue 9, “The Spectral Radiance Experiment (SPECTRE): Project Description and Sample Results”, [abstract, full article]
AGW Observer 
angelsandarmor said
This is a great paper, and explains to me some of the basic principles of th science. Indeed you not I’ve seen many people make the same claims, and your description neatly summarizes the science. One tiny suggestion I’d make: as a lay person I frequently need consult other resources to understand the terminology being used. Perhaps a glossary of terms on the site would help?
I appreciate that that is a great deal of work, but thought that might clarify the technical terms not only for people such as myself but deniers/climate sceptics and those sitting on the fence.
Otherwise, I’m very appreciative of the effort you have gone to make the science available to people such as myself.
Watchingthedeniers.wordpress.com
Ari Jokimäki said
Thank you for the suggestion. I appreciate the need for it but I think I’d rather look for some ready made glossaries. Perhaps I’ll try in the future to give links to the special terms if they happen to have wikipedia page or something like that. But I’ll keep this request in mind.
Here’s one example, a glossary from NOAA.
angelsandarmor said
Great – thanks Ari, much appreciated!
Gareth said
I see from the graph that emissions in the wavelength ca. 12-18um are about 150mW/m^2 (c/w total irradiance ~1kW/m^2. OK – what is this telling me? What would be the incremental effect per percentage (or per ppm) increase in atmospheric CO2 concentration in deg C average surface temperature? I’m curious to evaluate how sensitive the greenhouse effect is to increasing CO2 and whether or not it is largely saturated at current concentrations. TIA.
Ari Jokimäki said
I’m not sure if those kind of details can be seen in the graph. To me the graph just shows that there is thermal radiation coming from the atmosphere at the wavelengths of greenhouse gases. For some discussion on the problematics of trying to see differences in these kind of spectra, see for example Griggs & Harries (2007):
Click to access i1520-0442-20-15-3982.pdf
That’s for outgoing longwave radiation (OLR), but should be indicative of the problems relating to the downward londwave radiation (DLR) as well. However, there is one difference between OLR and DLR which I think is important. As you mentioned saturation, the OLR is measured from the top of the atmosphere and DLR is measured from the Earth’s surface. The saturation like conditions occur close to the surface, so DLR is measured in a place where one should see more saturation than in OLR’s case. That might complicate things. But there is one study that has measured the differences in different greenhouse gases from the DLR (Evans & Puckrin, 2006):
Click to access 100737.pdf
As you are looking at the saturation issue, you should read Plass (1956). Check end of the page 2 and beginning of page 3 here:
http://www.americanscientist.org/issues/feature/2010/1/carbon-dioxide-and-the-climate
I also have an article coming up on the saturation issue, stay tuned. 🙂
Ari Jokimäki said
I just noticed that there is a very similar argument than I’m making here presented in this the Science of Doom article (published before my article):
Harry Dale Huffman said
“…the graph just shows that there is thermal radiation coming from the atmosphere at the wavelengths of greenhouse gases.”
As a physicist, I have to tell you: This does not prove a greenhouse effect, it merely shows that those gases are present in the atmosphere. It says nothing about a supposed climatological effect of those gases. Read up on the historical use of absorption spectra, how for example helium was first found on the Sun, not the Earth.
Ari Jokimäki said
The author of the Science of Doom article I linked to just above your post seems to disagree with you. I think that the energy in the emission spectrum shown above must come from somewhere – i.e. greenhouse gases have absorbed the longwave radiation emitted by the Earth and the GHG’s are then emitting the absorbed energy as longwave radiation and part of that emitted radiation is seen as an emission spectrum when measured on the surface of the Earth looking up.
Thank you for the suggestion, I’m somewhat familiar with that story – it is a nice one. However, here we are discussing emission spectrum, not absorption spectrum. Absorption from greenhouse gases would be seen (and has been seen) when measured outside the Earth’s atmosphere looking down to Earth. Here we are discussing the downward longwave emission spectrum as seen on the ground looking up to the atmosphere. I think you probably mistakenly thought that we are discussing the measurements of outward longwave radiation (which would show an absorption spectrum). Absorption spectrum would indeed just show that the greenhouse gases are present – although the spectrum would carry also information about how much greenhouse gases are present and probably some other things I fail to remember right now.
Ari Jokimäki said
There was an error in my thinking here. Even the absorption spectrum of outgoing longwave radiation should be enough to prove that greenhouse effect exists because the OLR absorption spectrum shows that energy has been absorbed in the spectral bands of greenhouse gases and the absorbed energy should be re-emitted somewhere. As the re-emission occurs to random directions, we know that some of it will find its way back to the surface of the Earth. So, seeing the absorption bands of different greenhouse gases in OLR spectrum also proves that greenhouse effect exists.
Mark said
Minor point: Your link to Ellingson & Wiscombe (1996) doesn’t point to the paper at the moment.
Ari Jokimäki said
Thank you, Mark, AMS changed their URL’s to papers a while back and while the abstract links are redirected to the new URL, PDF links are just dead. That affects many of my posts. This one is now corrected.
MostlyHarmless said
Harry Dale Huffman is right – the DLR from greenhouse gases proves nothing w.r.t. the postulated greenhouse effect. The gases radiate according to their temperature. The fact that they radiate says nothing about how they acquired their heat energy.
Conduction of heat from surface to atmosphere and subsequent convection play a major role in weather and climate, yet the mechanism is assigned a tiny role in heat transfer in Global Energy Budget schemas.If conduction/convection had such a small role in domestic heating systems, few of them would work effectively, yet we know that they do.
What I’d like to know is this:Is the research qualitative (“We see the signature of GHGs in DLR”), or quantitative (“We see the signature of GHGs in DLR, and the radiation intensity confirms greenhouse theory”)? Even if the latter were true, water-vapour largely masks the effect of CO2; the former has a broader absorption spectrum. The Global Warming hypothesis requires unproven “positive feedbacks” to amplify the (generally agreed) small effect of increased CO2.
Ari Jokimäki said
You are welcome to point out the research that shows how the energy comes somewhere else than greenhouse effect and also matches observations as well as the theory based on greenhouse effect.
It is difficult to see your point here. Are you suggesting that convection has caused the global warming or that convection somehow makes CO2 not to cause warming? Huge amount of research exists on convection, so the first step here is to provide the research articles that show convection to be some kind of problem for the anthropogenic global warming theory.
Quantitative. Already in 1998 the match between the models and observations in this issue was excellent:
This argument was shown to be false over 50 years ago:
But go ahead and present us the recent research that shows how water vapor masks the effect of CO2.
We have already seen global warming, so your claim here is false. There is some uncertainty about some of the feedbacks, but that just concerns the question of how bad it gets in the future. Our best estimates seem to be suggesting at least about 2 K warming. Some of the positive feedbacks have also been observed already.
Next time, please provide evidence for your claims, so that we don’t have to ask them separately for each claim.
Harry Dale Huffman said
You are a piece of work, pretending to be a scientist. Any bright layperson who happens by and reads your article can tell you have not proven that the heat energy radiated by the co2 in the atmosphere came from the surface of the Earth. The radiation from the Sun is about 53% infrared, most of which is absorbed in going down through the atmosphere (except in a few “infrared windows”–note the co2 absorption region not in the pictured window). When I said absorption, I meant absorption, but you are too prejudiced to consider the possibility you are wrong, and you are obviously not looking for alternative ideas, because what I have just written is obvious. The radiation emitted by the gases in the atmosphere is heat energy, and is rapidly distributed throughout the atmosphere, and over all directions. It is omnidirectional, it doesn’t have the directional characteristics of, say, the Trenberth and Kiehl “energy budget” diagram used by the IPCC–and which (by the way) is defended as competent by ScienceofDoom, who doesn’t even know a blatant violation of the conservation of energy when he sees it (since he has posted his own “simple example” in defense of Trenberth’s cartoon, an example which violates energy conservation even more).
The “consensus” of “97% of all climate scientists” is incompetent. That is the real story, which will reverberate long after global warming has obviously changed to global cooling (it has already started). Don’t bother arguing with me, I just happened by; look up Syun-Ichi Akasofu, for example, and the article “Natural Components of Climate Change During the Last Few Hundred Years.”
Ari Jokimäki said
The “about”-page here contains this note: “I am not a professional climate scientist, but just an interested layman who has been getting familiar particularly to the observational side of the issue by reading the research papers on the subject.” Your claim is wrong, as you can see.
Sure, I cannot tell certainly for each photon where they came from, but as you are describing yourself, the carbon dioxide is absorbing thermal energy and then re-emitting it. If Earth radiates thermal energy in proper frequencies, then why would the carbon dioxide not absorb it? The carbon dioxide molecules don’t know if the thermal energy came from the Sun or from the Earth’s radiation. Therefore they must absorb also from the radiation that Earth itself is radiating and re-emit it to a random direction – some of it back towards the Earth. This is called greenhouse effect. Your own argumentation leads again to the situation that the emission spectrum shown above, as measured from the Earth’s surface, shows that greenhouse effect exists.