(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: H2O accounts for 95% of the greenhouse effect; CO2 is insignificant.
Answer: According to the scientific literature and climate experts, CO2 contributes anywhere from 9% to 30% to the overall greenhouse effect. The 95% number does not appear to come from any scientific source, though it gets tossed around a lot.
Please see this paper (PDF), the textbook referenced here, and this article at RealClimate.
There is a very important distinction to be made, as you will read if you follow the link to Real Climate, between water vapour's role in the Earth's Greenhouse effect and it's role in climate change. If you were to read through the table of climate forcings in the IPCC report or at NASA's page about forcings in its GCM, you won't find water vapour there at all. This is not because climate scientists are trying to hide the role of water vapour, rather it is because H2O in the troposphere is a feedback effect, it is not a forcing agent. Simply put, any artificial perturbation in water vapour concentrations is too short lived to change the climate. Too much in the air will quickly rain out, not enough and the abundant ocean surface will provide the difference via evaporation. But once the air is warmed by other means, H2O concentrations will rise and stay high, thus providing the feedback.
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Comments
View as Flat
Zarkov Posted 7:00 am
26 Dec 2006
yes it dwarfs CO2.
However as the CO2 is going up, water vapour is going down. Fully formed cloud is becoming harder to find in the skys, and "ice clouds" are on the increase.
Thus the scientific analysis leads to a dilemma.
[In my view the level of CO2 is an indicator only, indicating the amount of oil released into our environment]
LOL, is it global warming (real warming) or is it a tipping towards clear skys all year long and really is an underlying global cooling.
IMO, global cooling is actually happening and well, look out... Agricultural land prices will tumble.. and...
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homer13013 Posted 4:11 am
07 Mar 2007
-One of the first website that came up from a google search. Not much effort taken by this website to research. Numerous scientists quoted. Everything is referenced at the end of the aritcle. Brief Summary: we contribute about .28% to global warming.
-I heard a UN report came out that showed people who eat meat actually contribute more to global warming than all of the CO2 emitted by cars/trucks combined. Maybe we should just all become vegans...Because, I for one, love veggie burgers.
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Delay And Deny Posted 4:16 am
07 Mar 2007
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Coby Beck Posted 1:56 pm
07 Mar 2007
For example the author uses an EPA document
http://yosemite.epa.gov/oar/globalwarming.nsf/UniqueKeyLo ...
as its source for a GW potential multiplier to apply to atmospheric concentrations but due to the fact that the atmospheric lifetime of H2O is days, not years the 100 year GWP multipliers cited are entirely inappropriate. I note that this document does not include H2O in its GH forcing agents because H2O is a feedback, not a forcing.
The other fatal error the author makes is by ignoring the overlapping of absorption spectra of the various gases, this is what makes it a very complicated thing to quantify and in fact means that there is no single percentage of GHE that can be exclusively attributed to a given gas. You could arbitrarily reduced the contribution of one and increase another that absorbs in the same bandwidth and arrive at the same 100% total.
Seriously, beware of any source that claims such precision with no error bounds or uncertainty (ie CO2 is 0.28% of the GHE) Compare that to RealClimate's RealScience answer of CO2 is 9-30% of the GHE.
"The problem with people who have no vices is that they tend to have some pretty annoying virtues."
-- [paraphrased] Elizabeth Taylor
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Gar Lipow Posted 3:14 am
03 Apr 2007
A good Real Climate post on this can be found at:
http://www.realclimate.org/index.php?p=142
Again you are doing a great service with this series, and someone who follows your second link will get good information on this point. But I thought it important enough that you might want to consider updating the main post with it.
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GreyFlcn Posted 3:45 am
03 Apr 2007
Water vapor can be forcing in two minor ways.
Stratospheric water vapor, which is trapped in tropospheric methane gas.
Airplane contrails at high altitudes.
http://www.greyfalcon.net/forcing3.png
When they say scientists ignore water vapor.
No, they don't.
_
The difference is that it cannot be considered a forcing in the troposphere.
Since the amount of water vapor in the troposphere is directly proportional to the temperature.
Warmer it gets, the more it holds.
Colder it gets, the less it holds.
Any excess goes up there, and it condenses and rains out immediately.
And if all the water vapor were removed from the troposphere, it'd only take a mere 10 days to refill. (With most of it filling within the first 2 days)
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Coby Beck Posted 6:53 pm
03 Apr 2007
That's a good idea, it is such a short article I don't see how it could hurt.
"The problem with people who have no vices is that they tend to have some pretty annoying virtues."
-- [paraphrased] Elizabeth Taylor
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Gar Lipow Posted 8:26 am
05 Apr 2007
And Greyflcn: thanks for the correction.
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svstudent Posted 11:53 pm
02 May 2007
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Coby Beck Posted 3:53 am
05 May 2007
The reason for the difference is in the atmospheric residence time of a water vapour pulse vs a CO2 pulse. Because CO2 survives he seasonal cycles it has the chance to alter the climate, lasting many decades ensures it does. Water vapour will just not stay artificially elevated long enough to do that.
"What if this weren't a hypothetical question?"
-- unknown
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wxman03 Posted 6:06 am
05 May 2007
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corinne Posted 6:35 am
14 Nov 2007
""No Scientific Source?" Really?!
http://www.geocraft.com/WVFossils/greenhouse_data.html
-One of the first website that came up from a google search. Not much effort taken by this website to research. Numerous scientists quoted. Everything is referenced at the end of the aritcle. Brief Summary: we contribute about .28% to global warming."
Homer, the first website I clicked on that was cited as a source http://www.ecoenquirer.com/EPA-water-vapor.htm was clearly a spoof website along the lines of "The Onion" that appeared obviously designed by anti-environmentalists to make environmentalists look foolish. Either these geocraft.com people are stupid enough to mistake a spoof publication as a legitimate source (like the people who think Stephen Colbert is an actual conservative commentator) or they assume their readers are that stupid.
Don't tell me you're that stupid?
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Amazed Posted 8:04 am
14 Nov 2007
We had a great warming from 1900 thru the 1930's when we didnt have the man made Co2 amounts to cause it..nor the cars to create it. Then we had a cooling from the 1940's up to the 1970's and that was during a time of more Auto's on the road. Again Co2 didnt make it hotter or do anything else to effect the natural changes.
I see no effect change from any Co2 and nasa has reported that Co2 levels have gone backwards and not constantly increasing.
Better get your sleds ready!
"Lets go surfin'
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GreyFlcn Posted 8:28 am
14 Nov 2007
Water vapor spends on average about 2 weeks in the troposphere. And any excess condenses, and rains out.
The only cause for variation in the water vapor content of the troposphere is if some other forcing causes a warming in the troposphere.
Which actually gives a great explanation how a targeted warming in the troposphere by CO2 accumulation can be multiplied into a rather large warming.
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Wylie Posted 1:24 am
12 Dec 2007
Any and all comments appreciated.
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lauri Posted 5:44 am
29 Jan 2008
Some one mentioned that water vapor traps unequally different wave lengths of radiation. Also, that trapping would easily get saturated in those wave lengths it traps. a) Is this important for forcing? b) Does it mean that forcing is rather independent of amount of water vapor in the atmosphere? c) How does CO2 behave w/ respect to the same phenomenon?
I encountered a claim that the trapping of radiation that CO2 does, takes place in the first 10 meters above ground. So, if you double CO2 concentration, the same trapping takes place in 5 meters. Therefore, there is no increase in RF with an increase of CO2 concentration. Is it so?
People seem to use computer models to compute RF's of different concentrations. Why not set up chambers and simply measure radiation penetration at different concentrations?
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bogush Posted 6:10 pm
04 Apr 2008
The first is, how on earth does the atmospheric residence time affect anything if 95% or whatever of the global warming gases in the atmosphere are water vapour?
If I take two bathtubs and fill one 95% full and leave the taps running so that the water going in is matched by the water going out of the overflow.
And fill the other 5% full and turn the taps off and leave the original water in there for years.
Why am I more likely to drown in the 5% full bath?!?!?!
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bogush Posted 6:15 pm
04 Apr 2008
"Water vapor is a feedback, not a forcing. That is, the amount of water vapor in the atmosphere roughly depends on how warm it is from other causes - such as other greenhouse gases. Thus the percent of global warming attributable to water vapor is irrelevant, because warming from water vapor responds to other causes, and lags them.
But, just a minute, don't even the man-made global warmers admit that, yes, while the graphs of temperature and CO2 levels look very similar, when you look at them in detail the CO2 changes lag the temperature changes.
So doesn't that mean the CO2 is a feedback not a forcing?
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bogush Posted 6:26 pm
04 Apr 2008
So it's all our fault.
But, wait a minute, if they don't know what unknown, mysterious, mystery, unknown means caused the initial warming, how do they know the same unknown, mysterious, mystery, unknown means doesn't continue and cause the ongoing warming?
Also, doesn't drops in CO2 levels lag drops in temperature.
So the end and reversal of global warmings are also brought about by some unknown, mysterious, mystery, unknown means.
So, if, basically, they don't know what unknown, mysterious, mystery, unknown means start global warming.
And they don't know what unknown, mysterious, mystery, unknown means end global warming.
How can they have a clue what unknown, mysterious, mystery, unknown means cause its increase in between the two?
Never mind that man is the cause of it!
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bogush Posted 6:34 pm
04 Apr 2008
So it's all our fault.
But, wait a minute, didn't the scientist who ran the UN research on changes in atmospheric composition say that, oops, the man-made global-warming scientists don't make corrections for the CO2 loss from the ice cores with time and changes in their composition with increased pressure and that when you make the necessary allowances there is no appreciable change in CO2 levels from what would have been in the ice cores from pre-industrial times!
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stooben Posted 12:37 am
07 Apr 2008
"Cross a liberal on duty and he becomes a man of hurtling irrationality."
WFB, Jr.
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stooben Posted 10:28 pm
08 Apr 2008
"Cross a liberal on duty and he becomes a man of hurtling irrationality."
WFB, Jr.
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stooben Posted 5:17 am
15 Apr 2008
If you'll read this article, and, more importantly, the many responses, you'll see that CO2 as an insidious "forcing" agent is anything but settled science.
"Cross a liberal on duty and he becomes a man of hurtling irrationality."
WFB, Jr.
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thecure Posted 7:03 am
15 Apr 2008
FACT: Ice ages are NOT normal in climate here - after all, they've only been around for 100,000,000 years - Earth's been here for 4.5B. Thats only 2% of Earth's total history. 98% of the time - there was no ice.
FACT: If man is an evolutionary advance, s/he sure is a strange one. We 'evolved' bigger brains, but lost all the fur, nails and climbing ability which would protect us from natural predators.
FACT: CO2 was higher than now at ALL times since before the ice ages. From Day 1 of the planet right through 100,000,000 BC CO2 levels are orders of magnitude higher than they are now. Earth was warmer - with no ice.
FACT: Ice is a 'new' factor at sea level on Earth.
FACT: There is more CO2 dissolved in the oceans, in coal, in crude oil, oil shale and trapped in limestone and rock than is in the atmosphere today. However, it ALL was in the atmosphere at one point. Oil and coal are carbon fossils. Dead things essentially.
THEORY: AS all that carbon was permanently removed from the atmosphere the planet cooled off. We got ice, snow, and then ice ages.
THEORY: What if man, with bare skin, no hair, no claws or sharp teeth, is the evolutionary adapation of life on this planet designed to free the trapped CO2 and warm the planet back up? WE FIRST started buring coal and oil for warmth and light since we are cold without clothing and artifical heat.
WARNING: Beware of unintended consequences, maybe we're burning all this fossil fuel for a reason - mother Earth , Gaia, wants us too . . . .
Insert Witty Phrase Here
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barry schwarz Posted 5:52 pm
15 Jun 2008
The difference between CO2 in the post-industrial age and water vapour is that CO2 is accumulating in the atmosphere due to our industry, whereas average (global) water vapour doesn't accumulate absent any other forcing. Rather water vapour concentration in the atmosphere is a function of temperature and pressure. If the temperature/pressure goes up, more water vapour.
Because the response time of water vapour is, relative to CO2, immediate, then water vapour is seen as a feedback to other climate parameters - temperature and pressure.
According to AGW theory, CO2 accumulation is continual and rising. If this incurs higher global temperatures, then more water vapour will accompany the rise, 'trapping' more upwelling infrared and exacerbating the heating effect.
To reply to a couple of posts upthread, WV does indeed 'rain out' of the atmosphere in relatively short order when encouraged by (downwards) changes in temperature/pressure, but this happens at a local level. No one is saying that WV 'rains out' across the whole globe at the same time. Rather, WV responds locally and concentrations go up and down at different points on the globe on very short time scales.
However, with rising global temperatures, the global average concentration of WV will go up, amplifying the rise.
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barry schwarz Posted 6:13 pm
15 Jun 2008
Hi all,
I've been debating this particular issue for about 6 months, and I won't festoon this post with links, because there are few I've found on the web that get to the kernel of the matter - radiative absoprtion - and certainly not broadly enough to satisfy an honest inquiry.
[This is the best single study I've found (PDF). I believe Coby has linked to it in the top post]
The way greenhouse gases retain heat is by absorbing, re-emitting, and reabsorbing and re-emitting infrared radiation welling up from the Earth's surface. If the GHGs weren't there, the infrared radiation would escape to space and we'd be living (or dead, rather) on a very cold planet.
CO2 absorbs upwelling infrared radiation (IR) mainly (but not only) in the 15 micron wavelength range. But water vapour (WV) absorbs in many bands, and significantly part of the 15 micron band. If you looked at an absorption graph, you'd see a 'spike' for CO2 in the 15 micron range, and a 'slope' cutting across the 15+ micron range, being the WV absorption. WV also absorbs at lower wavelengths, as does CO2.
15 micron absorption of IR by CO2 is practically saturated in the middle of the 15 micron range, but there is more absorption possible either side. Adding more CO2 'fattens' the spike - a bit like painting a wide black stripe across a window, adding more CO2 is like adding a fine line of paint either side of the wide stripe, which prevents more light (IR) passing through the window. WV's absorption profile laid over this would be like painting a diagonal stripe that cut across the original one. If the wavelength values are increasing to the right, WV would cover the whole right hand side of the window and slope down to the left across the CO2 stripe. If you can picture this, that leaves mainly the left hand slope of the CO2 spike (very steep) available for absorption. Here is where most of the action is.
In the actual atmosphere, WV fluctuates dramatically. In arid areas, over deserts and the poles, the WV absorption profile is less pronounced. The CO2 15 micron 'spike' stands out more, and therefore the absorption of IR by CO2 is more pronounced.
At this point in the debate, honest skeptics want hard data from spectral absorption studies. There are hundreds, stretching back to the 1950s, when the US airforce began measuring the upper atmosphere for military purposes (thereby discovering that the atmosphere has many layers, and is not a single slab, as was thought until then). Early studies were ground-based at high altitude, from weather balloons and high-flying aircraft. Satellites were later used for spectral analysis, measuring from the top of the atmosphere down, and perpendicular to the surface of the Earth at altitude. Time series studies exist showing a rise in CO2 levels, and changes in thermal activity. Here is some of the hard data honest skeptics are looking for - at this resolution.
There is a database (HITRAN) that gives spectral absorption data for various gases. As with WV and CO2, there is some overlap in which gases absorb what wavelength of radiation. In Earth's atmosphere, there is a 'window' between the 8 and 12 micron band where there is virtually no absorption going on, and through which upwellng infrared radiation passes out from the surface to space virtually unimpeded. Adding more CO2 impinges on this clear part of the spectrum, at the 12 micron end.
However, the study is so complex, with instruments usually only capable of studying a few bandwidths at once, and the layers of the atmosphere needing to be taken into account, that you'd need to read a mountain of studies to get a whole picture. At Spencer Weart's website on the history of climate science, he recommends that one would need to go to a library and read at least one fat book on atmospheric radiative transfer to get the kind of data and understanding needed to get a fix on the drill-down 'facts'. He also points out that much of the spectral analysis was done 40 years ago, and many of the studies have not been transferred to the internet. IOW, to get to the guts of this issue, at the resolution of radiative transfer and absorption profiles, including times series and under different humidities, is probably impossible via the web. Not to mention that most studies that are available cost money to view.
There is a lot of pseudo-science on the topic. When a paper is cited, check the author's credentials. There are quite a number floating around written by (for example) neuroscientists (TJ Nelson), computer engineers (Petschauer), and experts in geomagnetics-regarding-military-weapons (Slade somebody-or-other, via the late John Daly's website).
I guess I want to warn you that absolute resolution on this, if pursued honestly, rigorously and to the enth degree, will leave the querant unsatisfied if they restrict their travails to the web. And I thought I'd point this out to you, Coby, because it's well to acknowledge limitations when acting as a conduit for information.
My take - I think it is unreasonable to think that mainstream climate theory is ignoring the role of water vapour in the atmosphere. I searched for the phrase (with the European/Australian spelling of 'vapuor') in the pdf files of the 2001 and 2007 IPCC reports. I got hundreds of hits, but the IPCC reports do not detail the spectral properties of WV and CO2 - that is too fine a resolution for the purposes of the report (if that kind of information was included, the document would be a hundred times larger and quite impractical). For that information you not only have to go to the studies listed in the relevant chapters, but also the studies those studies reference, and the studies those studies reference and so on, and pretty much all of these are pay per view and many wouldn't be found on line.
You have to be extremely bloody dedicated or slightly mad to get to the absolute bottom of this. I haven't made up my mind which category I fall in.
Hope this post was useful, or at least, that I spare some sincere sojourner the months of googling I went through. On the way, though, I learned a lot of vicarious arcana and useful stuff to understand what goes into the study of this particular subject.
May good tidings and intellectual honesty make a home in your hearts and minds,
barry.
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barry schwarz Posted 6:17 pm
15 Jun 2008
http://www-ramanathan.ucsd.edu/publications/Ramanathan%20 ...
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