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Evaporating the water vapor argument

Posted on 30 September 2007 by John Cook

A new study Identification of human-induced changes in atmospheric moisture content (Santer 2007) was published last week, inspiring me to revisit the water vapour argument. A popular skeptic argument (well, a ranking of #20 is no mean effort) is that water vapour is the most important greenhouse gas, rendering CO2 warming relatively ineffective. Water vapour is indeed the most dominant greenhouse gas. The radiative forcing for water is around 75 W/m2 while carbon dioxide contributes 32 W/m2 (Kiehl 1997). Water vapour is also the dominant positive feedback in our climate system and a major reason why temperature is so sensitive to changes in CO2.

Unlike external forcings such as CO2 which can be added to the atmosphere, the level of water vapour in the atmosphere is a function of temperature. Water vapour is brought into the atmosphere via evaporation - the rate depends on the ocean and air temperature and is governed by the Clausius-Clapeyron relation.

If extra water is added to the atmosphere, it condenses and falls as rain or snow within a week or two. Similarly, if somehow moisture was sucked out of the atmosphere, evaporation would restore water vapour levels to 'normal levels' in short time.

Water Vapour as a positive feedback

As water vapour is directly related to temperature, it's also a positive feedback - in fact, the largest positive feedback in the climate system (Soden 2005). As temperature rises, evaporation increases and more water vapour accumulates in the atmosphere. As a greenhouse gas, the water absorbs more heat, further warming the air and causing more evaporation.

How does water vapour fit in with CO2 emissions? When CO2 is added to the atmosphere, as a greenhouse gas it has a warming effect. This causes more water to evaporate and warm the air more to a higher (more or less) stabilized level. So CO2 warming has an amplified effect, beyond a purely CO2 effect.

How much does water vapour amplify CO2 warming? Without any feedbacks, a doubling of CO2 would warm the globe around 1°C. Taken on its own, water vapour feedback roughly doubles the amount of CO2 warming. When other feedbacks are included (eg - loss of albedo due to melting ice), the total warming from a doubling of CO2 is around 3°C (Held 2000).

Empirical observations of water vapour feedback and climate sensitivity

The amplifying effect of water vapor has been observed in empirical studies such as Soden 2001 which observed the global cooling after the eruption of Mount Pinatubo. The cooling led to atmospheric drying which amplified the temperature drop. A climate sensitivity of around 3°C is also confirmed by numerous empirical studies examining how climate has responded to various forcings in the past.

Satellites have observed an increase in atmospheric water vapour by about 0.41 kg/m² per decade since 1988. A detection and attribution study (Santer 2007), otherwise known as "fingerprinting", was employed to identify the cause of the rising water vapour levels. Fingerprinting involves rigorous statistical tests of the different possible explanations for a change in some property of the climate system.

Results from 22 different climate models (virtually all of the world's major climate models) were pooled and found the recent increase in moisture content over the bulk of the world's oceans is not due to solar forcing or gradual recovery from the 1991 eruption of Mount Pinatubo. The primary driver of 'atmospheric moistening' was found to be the increase in CO2 caused by the burning of fossil fuels.

Basic theory, observations and climate models all show the increase in water vapor is around 6 to 7.5% per degree Celsius warming of the lower atmosphere. The observed changes in temperature, moisture, and atmospheric circulation fit together in an internally and physically consistent way. When skeptics cite water vapour as the most dominant greenhouse gas, they are actually invoking the positive feedback that makes our climate so sensitive to CO2 as well as another line of evidence for anthropogenic global warming.

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Comments 1 to 35:

  1. Incidentally, it is fun to point that burning hydrocarbons from fossil fuels is also the only net addition of water vapor to the system, except for a comet impact.
    The simplest case, methane (natural gas) goes like this if I'm not mistaken (fully developed, with the "real" molecule numbers): 3CH4+6O2 gives 3CO2+6H2O. For every molecule of methane burned, 3 molecules of water are added to the atmosphere. It obviously does not change anything to the John's argumentation above and the existing research results, but, even in the absence of that evidence, arguing that water vapor is a more potent GHG would not undermine the argument that we should veer away from fossil fuels.
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  2. Philippe, your chemistry is a little askew. Natural oxidation of methane is a chemical process which I don't believe would fall under your definition of burning, yet has the same chemical equation. Why isn't that adding water vapor to the system? Or respiration, or a gazillion other processes occuring all over the globe on, under and above the surface, continually removing and adding water to the atmosphere in a wonderfully dynamic process, varying over hours and millenia, over elevation and geographic location, in ways that we continue to struggle to accurately model and understand.

    Despite what John would have you think in the analysis above, more than one climatologist is continuing to study the effect of water vapor on global climate. To blithely state that the global atmospheric water vapor content is essentially a simple function of global temperature because it is governed by the Clausius-Clapeyron relation (John, is that an unfair paraphrase?), should make a climatologist wince. For example, this relationship is approximately true only near the ground-- and only higher altitude (free troposphere) water vapor effects earth's cooling (precisely because it is colder than the earth), and up here, water content is governed not by C-C relation, but by transport processes such as the rise/fall of warming/cooling air. I can give references. In fact, a quick google just pointed me to IPCC TAR Ch7.2.1 Physics of Water Vapor and Clouds.

    John, although I find your site a delight and in general think you have the right mind-set, you shouldn't over-simplify just to show up the global-warming skeptics. Or you may fall into a similar trap as Philippe and over-extend your reach attempting to bolter to eagerly your already-held belief. Specifically, here I think you are attempting to stifle a scientifically-valid continuing attempt to understand a complicated process, by prematurely asserting the issue is resolved, with a simplistic and/or flawed line of reasoning. A trait I greatly fault Al Gore for sharing.
    Regards,
    Kenton
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    Response: Good feedback, kenton. I'm not saying we should stop studying water vapor systems - if I give that impression, I'll revisit my words. In fact, I think climate will never be completely understood - there'll always be nooks and crannies to further understand. But I do believe we know enough to act on reducing CO2 emissions.

    Re over-simplification, that's a framing issue I'm still working out. I'd like to make the science accessible without compromising scientific accuracy. The point of this page is not to say water vapor is completely understood but that rather than contradict anthropogenic global warming, it is actually consistent with it. But I will have another look at my treatment of the C-C relation so thanks for the feedback
  3. Continued study. Very recent but I didn't write down all the details so you may have to dig a bit.

    Spencer etal in Geophysical Research letters Vol 34 have a paper on Rainfall events in the tropics. It appears to clearly show empirical evidence on Lindzen's proposed "iris effect" of water vapor. In addition to being very important to how storms develop over time, it appears to reduce any positive effect of increased water vapor on temperature by about 75%
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  4. "Water vapour is also the dominant positive feedback in our climate system and a major reason why temperature is so sensitive to changes in CO2."

    Here you've gone right over the edge into circular thinking. We need some actual evidence.
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  5. Good point Kenton. However, for all practical purpose, the carbon/hydrogen compounds locked deep in the crust are not normally available to natural processes. I may not have expressed it very well, but it was in that sense that I said WV from FF combustion constituted a net addition.

    I assume that you were refering to methane from digestive processes or fermentation. Those and other natural processes have to somehow combine carbon/hydrogen that is available. Geologic events can make a bunch of it so from time to time, but not exactly on the scale allowed by the wholesale extraction and combustion of fossil carbon that we have practiced.

    I think it was a little bit of a jump from you to conclude that I was merely reinforcing already held beliefs. I am well aware of a number uncertainties in climate science or other sciences. Believe me, it always makes me somewhat uneasy when I have to administer medications to patients and the mechanism of their action is unknown (happens a lot). You should have a difficult time finding a thread where I describe and assert such beliefs. You may not have noticed that I never attempt to forward any doom/gloom message or anything of the sort. However, just like the water vapor oversimplifications make you cringe, some things like "Global Warming on Pluto" as an attempt to explain things on Earth make me cringe too. I do try to keep myself aware of the existing state of the science and I do try to see where the weight of the evidence is leading, which is not an easy task for a layperson. The mess of overpolitization (inflamed by many skeptic "extremist" organizations) and innumerable clumsy or overhyped press releases certainly does not facilitate that task.
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  6. I think the water vapor issue is viable, as humans force 37 times more water vapor into the air than CO2 in the US. This ratio could be much higher in other parts of the world. Forced evaporation does have an effect because you are doing it daily, in the most arid parts of the US. Here’s my two part video on it.



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  7. My video did not include contrails, but the moisture from airplane contrails also causes the daily high to low temperature range to decrease. The daily temperature swing from high to low increased in the few days after 9/11 when all planes were grounded and the upper atmosphere had less forced moisture.

    http://facstaff.uww.edu/travisd/pdf/jetcontrailsrecentresearch.pdf
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  8. “When looking at water vapor, the amount humans have added to the atmosphere today is the sum of the past few weeks (at MOST), since water has its own equilibrium and just rains out.”
    ------------------
    I agree that the water vapor will rain out, but we are adding the water vapor in a daily process, making the land areas artificially more humid (every day) than they would have been. This man made humidity reduces the heat that is radiated back into space.

    Seventy percent of the earth is covered with water. Let’s look at a “Water World” type earth with no land. The humidity created by being 100% ocean would cause the planet’s temperature to increase. We would have very small daily temperature swings, at any location and I doubt that we would even have ice caps at the poles.

    What if the earth was 100% land with no open water? The result would be a planet with no humidity, with big daily temperature swings, but with the net effect of having a much colder planet.

    The effect of our forcing water into the atmosphere is similar to changing the surface water from 70% to say 75%. It will have and effect on the earths temperature. CO2 is not a factor in these examples and it’s not a major factor in global warming.
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  9. During the Cretaceous Period the earth was about 80% covered with water and tropical sea surface temperatures may have briefly been as warm as 42 °C (107 °F), 17 °C (31 °F) warmer than at present and deep ocean temperatures were as much as 15 to 20 °C (27 to 36 °F) higher than today's. (Per Wikipedia)

    http://en.wikipedia.org/wiki/Cretaceous

    -----------------

    “CO2 levels are usually invoked to explain Cretaceous warmth and the flat Cretaceous temperature gradient. This makes sense, since the very active mid-ocean spreading ridges might well have bee associated with out-gassing of CO2 from deep within the Earth. Unfortunately, the geology of the period and stable carbon isotope records, don't really support the idea as well as they might.”

    “Even the most sophisticated quantitative models can't reconstruct the flatness of the Cretaceous temperature gradient. Either our temperature estimates are off, or some important factor is missing from the models. Since dinosaurs and semi-tropical vegetation are known from within 10° of the Cretaceous poles, the problem is likely to be with the theory.”

    http://www.palaeos.com/Mesozoic/Mesozoic.htm

    Take a look at the temperature vs latitude chart. With the earth being cover 80% with water, the “Water World” type moisture effect was coming into play. IMHO
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  10. John
    The argument made by BestTimesNow above here is what I was referring to when I remarked about the Clean Air Act of 1975 in the U.S. a while back. Not only does every car with a cat push out more CO2, it pushes out more water vapoer (both by design) and additionally makes the water vapor acidic from Sulphur Dioxide.
    This issue becomes more interesting all the time.
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  11. John

    If CC is acceptable then we can simplify still further and employ the "Boltzmann Atmosphere".

    As per this effect because of the drop in pressure at higher elevations the mole percent of various gases would drop exponentially depending on their molecular weights and the temperature. An actual calculation shows that at higher elevations the water vapour content is far higher compared to the carbon dioxide levels starting from identical surface levels ! Hence any CO2 generated at the surface should stay practically near this same surface !

    This would amplify the effect of water vapour higher in the atmosphere but would reduce the forcing of CO2 on the water vapour since CO2 amounts would be negligible at higher elevations

    Very crude I know but somewhat interesting !

    Incidentally Clausius and Boltzmann were in the same era more or less !
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  12. August 7th....still no sunspots (Spaceweather.com)
    Query: If the apparent lag between global T and sunspot activity is 10 yrs then the current cooling (IF it continues) should be visible in the sunspot record of around 10yrs ago....or is 10yrs a bit too close to the average sunspot cycle?

    The water vapour effect should be split in two...water vapour uncondensed and water vapour wholely or partially condensed (cloud) as cloud cover can both increase warming or decrease TSI dependent on the cloud thickness.
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  13. Water vapor is the most abundant and important greenhouse gas and has been responsible for most of the climate change, for millions of years.

    Let’s look at progression of 5 examples of the Earth, starting with the warmest Earth, so you can see the effect on the planet. To keep things simple, we’ll set the composition of dry atmosphere, to the same as the present time, in all examples, so that we can see the effects of the water vapor in the air.

    Earth 1 – Water World

    We’ll start out with a hypothetical “Water World” type Earth, without any land. This will be the overall warmest Earth, with no ice caps at the polls.

    Why would it be warmer than the present day Earth? Water just rains out.

    Climate models are not required, just basic understanding and logic to find the answer.

    What’s different in “Water World”? All elevations are at sea level in “Water World”, so the height of atmosphere (greenhouse effect) is at a maximum level all over the world. The very humid, middle latitudes will be the warmest, with no relief, with the humidity. If it rains, the moisture in the air will be replaced very quickly. This part is similar to the very humid, present day, tropical ocean areas, but now covers 100% of the middle latitudes in “Water World”.

    Also, because of the insulating effect of the very moist atmosphere and unrestricted ocean currents, the middle latitudes (45N to 45S) will have a very constant, but warm, temperature with only a few degrees temperature swing between the daytime highs and the morning low temperature.

    The warm water from the middle latitudes will also mix with the polar oceans due to the unrestricted ocean currents, this will cause these regions to be much warmer than our present time polar regions, and there will not be ice caps at the poles. The air in the Polar Regions will also hold more moisture than our present time polar regions and will add to the greenhouse effect.

    Earth 2 - Cretaceous period type land mass (see map)

    http://en.wikipedia.org/wiki/Image:LateCretaceousGlobal.jpg

    Some low elevation continents are formed and cover 20% of the surface of the Earth. The land mass will disrupt the ocean currents and will allow the Polar Regions to cool. The middle latitudes will still be very humid (similar to Florida) because the most of the land mass will be at low elevations. Some of the larger continents will allow areas of lower humidity, which will allow some cooling at night. This planet Earth 2 will be cooler than Earth 1, but still very warm due to the greenhouse gas, water vapor.

    Earth 3 - Paleogene (Eocene) period type land mass (see map)

    http://en.wikipedia.org/wiki/Image:Paleogene-EoceneGlobal.jpg

    The continents now cover about 25% of the Earth and mountain ranges are forming. Although ocean currents are a little more restricted than Earth 2, it’s the larger continental areas, with mountain ranges that will allow Earth 3, to be cooler than Earth 2.
    As the prevailing winds pass over the mountains, the moisture in the air precipitates out, allowing for large areas of lower humidity, over some of the continents. The large areas of low humidity allow for even more night time cooling. Planet Earth 3 will be cooler than Earth 2, but still very warm due to the greenhouse gas, water vapor, but the water vapor is loosing its grip on keeping the Earth’s temperature elevated.

    Earth 4 – Pre Industrial Revolution (see map)

    http://www.mapsofworld.com/world-maps/image/world-lat-long.jpg

    The continents cover about 30% of Earth 4 and very high mountain ranges have formed. Ocean currents are very restricted, with the connection of North and South America and Europe, Asia and Africa forming large land areas. The vast land areas of lower humidity allow the middle latitudes to cool. Night time cooling is becoming greater over larger areas of Earth 4. (Just think back to Earth 1) Some of the higher mountain ranges remain snow capped all year long. Earth 4 is much cooler than Earth 3.

    Earth 5 – The present day Earth

    Due to the extreme population growth, humans are having an effect on the climate. Millions of acres of arid land have been converted into farms and many fields are irrigated with up to 60” of water per year. The effect of irrigating millions of acres is similar to increasing the amount of the Earth that is covered with water. Most of the irrigation water is evaporated on a daily basis, which increases the greenhouse gas, water vapor and contributes to global warming.
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  14. How Much Water Vapor Are We Adding?

    From the report:

    Climatology and Trends of U.S. Surface Humidity and Temperature

    Climatological annual and seasonal dewpoint, specific humidity, and relative humidity maps for the United States are presented using hourly data from 188 first-order weather stations for the period 1961–90.

    With extended datasets for the period 1961–95, trends in these same variables and temperature are calculated for each of 170 stations and for eight regions of the country. The data show increases in specific humidity of several percent per decade, and increases in dewpoint of several tenths of a degree per decade, over most of the country in winter, spring, and summer.

    Locally, anthropogenic modification of the hydrological cycle may be more important. Within the conterminous United States, the U.S. Geological Survey has estimated that consumptive use of water in agricultural irrigation contributes 100 billion gallons of water per day to the atmosphere, compared with 2,800 billion gallons per day from evaporation and transpiration from surface water bodies, land surface, and vegetation (van der Leeden et al. 1990). In dry regions during the growing season, the ratio of consumptive use to natural evaporative sources may be greater, and it is possible that long-term increases in evaporation from irrigated fields may be large enough to influence the surface trends at some stations. Other confounding influences may affect the trends presented here. However, the spatial consistency of the trends leads us to speculate that they are not primarily due to local phenomena but represent regional, indeed national, increases in near-surface specific humidity.

    http://ams.allenpress.com/perlserv/?request=get-document&doi=10.1175%2F1520-0442%281999%29012%3C0811%3ACATOUS%3E2.0.CO%3B2

    ---------

    The amount of water we are adding to the atmosphere is substantial. The AMS report above says we are adding 100 billion gallons per day through agricultural irrigation, but we are really adding a total of about 160 billion gallons per day, in the USA. (Watch my two videos, above to see an explanation)

    Humans are increasing, the daily amount of water added to the air, by about 5.7%, over natural sources, in the USA.

    160/2,800 = 5.7% increase of daily moisture added to the air.

    I am using the USA, as an example, because of the data available, but I think other parts of the world, such as China and India may have even larger contributions for anthropogenic increases of water vapor, the largest greenhouse gas.

    Again:
    The effect of our forcing water into the atmosphere is similar to changing the surface water from 70% to say 75%. It will have and effect on the earths temperature. CO2 is not a factor in these examples and it’s not a major factor in global warming.
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  15. BestTimesNow:
    It seems to me you have taken data for the USA and then used that as a base for the global condition...?

    I don't disagree with your viewpoint on water...as a major ( possibly THE major) moderator in the climate system...but it has to be viewed as a complete subsystem which would include solid, liquid, gaseous phases as well as atmospheric condensate (clouds).
    Human activity may well be adding substantially to part of this cycle but this simply shifts the heat-balance..
    ( which is what climate is all about)....higher vapour levels eventually ends up as higher precipitation.
    In any event, whatever factors we choose to 'blame', there remains this: There is a limit to just how much heat can be retained in the system because there is a limit to how much is coming in. Increased CO2 or water vapour cannot 'add' anything that is not already there, they can only moderate the rate at which heat is lost.
    Heat in = Heat out, No?
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  16. BTN: Post script: be careful.....the next thing that will happen is that the alarmists will start trying to limit w.v. emissions ( I have a 95% confidence in this)
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  17. My god, all that extra Dihydrogen Monoxide in the environment! How horrible! What are we going to do!!!

    The dangers of Dihydrogen Monoxide
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  18. re #15

    "Heat in = Heat out, No?"

    No. Heat in doesn't equal heat out. With enhanced greenhouse forcing under constant insolation, Heat in is greater than Heat out (Heat in > Heat out)...in other words it gets warmer, until the effects of the enhanced forcing reach equilibrium. At that point Heat in does equal Heat out, but the system retains a greater amount of thermal energy. The world is warmer.

    That's not difficult to understand.

    And as we all know rather well, since simple physics, theory, simulation and real world measurements indicates this to be the case, a warmer atmosphere supports a larger water vapour concentration, and so as the earth warms under the influence of enhanced atmospheric CO2 concentrations, this warming results in an enhanced water vapour concentration. Since water vapour is itself a very strong greenhouse gas, this results in feedback warming.

    So enhanced atmospheric CO2 "adds" thermal energy (warmth) to the earth's climate system, and the resultant enhanced water vapour concentrations "adds" additional thermal energy (warmth). So it really requires rather awesome bottom-squirming semantic quibbling to pursue the fallacy that enhanced greenhouse gas concentrations "cannot "add" anything"...

    ..or are you suggesting that the greenhouse effect doesn't exist?!
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  19. Chris, you seem to have missed my point which is there is a limit to incoming heat and therefore a limit to the amount of energy that can be 'retained' by GG effects. So there is an upper temperature limit ( which we may not find to our liking) No?
    And yes, maybe I am playing with semantics but I don't see GG's 'adding' anything....only moderating the rate at which heat is lost.
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  20. Yes there is a limit to incoming electromagnetic radiation. I expect that there is an upper temperature limit. Perhaps Venus might give us a clue as to the upper temperature limit that is possible due to the "amount of energy that can be "retained" by GG effects". And yes, we might very well not find that to our liking.

    Of course GG's are "adding" something. They are adding thermal energy to the Earth's atmosphere, surface and oceans.
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  21. Venus?
    A lot nearer to the sun than the earth so TSI is a lot higher.
    CO2 concentration (if I remember rightly) is 30,000 times greater.
    Galileo probe showed an enormous amount of IR being retained by sulphuric acid cloud cover.
    No atmospheric water as it has all been dissociated and blown away ( Venus has virtually no magnetic field.
    Not a good comparison. So, no, Venus gives us no clues at all.
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  22. Well yes Venus gives us an idea of what can happen when a greenhouse effect runs out of control.

    Of course it's not going to happen on Earth. However we do know the total amount of potentially accessible fossil fuels, and if all of this was dug up and burned along with all the methane hydrates and shales and tar sands and peat and all forms of coal and gas and oil, the total warming would be rather dramatic.

    New Scientist did a report a year or so ago of an analysis of the projected warming...around 12 oC I think.

    So if we continue burn fossil fuels with present gusto we do have the potential to add a rather awesome amount of CO2 (and water vapour) into the atmosphere, and this will add a rather large amount of thermal energy to the Earth's climate. And of course since the time to achieve the new equilbrium temperature lags the forcings by a significant amount, the Heat In will be out of balance with the Heat Out for a while until the climate system adjusts to fluctuate around a new equilibrium temperature that is higher than it would be without the additional greenhouse forcings.

    That's all pretty obvious isn't it!
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  23. Careful Chris...it looks like you're suggesting AWV might be having some effect after all.....
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  24. Well yes, it's all about the evidence Mizimi, and not about trying to trap perceived "opponents" with semantic games!

    So it's pretty uncontroversial that enhanced atmospheric CO2 results in enhanced water vapour (this can be measured in the real world) as a feedback to CO2-induced warming. A warmer atmosphere promotes the enhanced atmospheric partitioning of water vapour. We can call this WV feedback AWV since it's an indirect a consequence of our CO2 emissions.

    However the effect of spraying water/water vapour into the lower atmosphere (from cooling towers and such like) has a minimal net contribution to greenhouse-induced warming, since this excess just comes straight out of the atmosphere within a very short period afterwards...

    So one needs to be clear about what "AWV" one (or two in this case!) is (are) talking about!
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  25. "(Washington, DC) The Environmental Protection Agency is seeking to classify water vapor as a pollutant, due to its central role in global warming. Because water vapor is the dominant greenhouse gas in the atmosphere, accounting for at least 90% of the Earth's natural greenhouse effect, its emission during many human activities, such as the burning of fuels, is coming under increasing scrutiny by federal regulators.

    Until now, the carbon dioxide produced during the burning of fuels has been the main concern. The extra carbon dioxide causes a manmade enhancement of the greenhouse effect. But water vapor is also produced by combustion of most fuels, as well as by industry and utilities that use water for cooling. The EPA would be able to regulate its manmade sources if it is classified as a pollutant.

    EPA Director of the Department of Pollutant Decrees, Ray Donaldson, said, "Back before carbon dioxide was dangerous, we simply assumed that water vapor was also benign. But all reputable scientists now agree that the increased water vapor content of the atmosphere from such sources as burning of fuels and power plant cooling towers will also enhance the greenhouse effect, leading to potentially catastrophic warming."

    http://www.ecoenquirer.com/EPA-water-vapor.htm

    see post #16
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  26. Very funny Mizimi

    I particularly liked the "White staffer" Lew Moninsky!
    (The Greenpeace "spkesperson Rainbow Treetower is a bit obvious...)
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  27. Thank you, Chris.

    Mizimi's little docudrama is telling because its humor depends on the listener being scientifically illiterate or willing to make oneself temporarily illiterate for the sake of an ideology.
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  28. #27

    Douglas,

    LOL! It is very ironic that your comment "its humor depends on the listener being scientifically illiterate or willing to make oneself temporarily illiterate for the sake of an ideology" applies equally well to the vast majority of AGW alarmists.
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  29. Your comment doesn't make much sense Healthy Skeptic. What humor are you referring to with respect to "the vast majority of AGW alarmists"?

    Can you give us an example please? After all Douglas and I are referring to something rather specific. You seem to be making a generalized assertion about something and it's not obvious what you're referring to.

    Example please...
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  30. Sorry Chris,

    Obviously one first needs a sense of humor to make sense of humor.
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  31. I can tell you that it is not insignificant to evaporate 100 billion gallons of water per day and it takes an enormous amount of energy to do so. I think it takes approximately 1500 btu to evaporate 1 pound of water to vapor form. Each gallon of water should be about 10 pounds if I recall correctly. So we evaporate an extra trillion pounds of water a day. I wonder if they consider all the surface area of ponds and swimming pools as well as irrigation? Did you know that Texas had more surface water area than Minnesota about 10 years ago?
    So, this process is transferring massive amounts of energy into the atmosphere whereas 50 years ago this was NOT occurring this way; so what is the affect of doing that? Could it be producing larger and more powerful storms as we have been witnessing in the last 10 or 15 years? That is my opinion! If nothing else it is putting all that energy into the air for a fact.
    Consider that a jet plane is dumping water at approx 2000deg F into the stratosphere where this was simply not happening 50 or 60 years ago. Burning that fuel produces 5 pounds of water vapor for each pound of fuel and I know that the jets burn a lot of fuel and there are about 4000 planes in the air at any given time over the usa.
    I only ask that ALL things which can contribute to any warming be considered and not simply dismissed without having any proof they are not involved. Be scientific!
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    Moderator Response: [Daniel Bailey] As Phil rightly points out, atmospheric water vapor excesses condense out, equalizing within a 9-day period. As one newly come out of the darkness of the Internet to Skeptical Science, Welcome! There is an immense amount of reference material discussed here and it can be a bit difficult at first to find an answer to your questions. That's why we recommend that Newcomers, Start Here and then learn The Big Picture. I also recommend watching this video on why CO2 is the biggest climate control knob in Earth's history. Further general questions can usually be be answered by first using the Search function in the upper left of every Skeptical Science page to see if there is already a post on it (given the plethora of posts [I get paid extra for using big words and alliteration :-) ] odds are, there is). Or you can search by Taxonomy. If, after searching, you cannot find an answer to a question, post it on what you think to be the most appropriate thread and someone will get back to you fairly quickly. As always, please compose your comments with adherence to the Comments Policy in mind. Finally, please use the Preview function to ensure your comments are representative of what you intend for them to say. Thanks!
  32. electroken - please read the post. You can evaporate more water but it also condenses so amount of water in atmosphere is function of temperature. Nonetheless, the maths is done on the basis of actual measured amounts of water vapour in atmosphere.
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  33. electroken: "Texas had more surface water area than Minnesota about 10 years ago?"

    I knew the drought was bad, but your comment really puts it in perspective. As do these maps, from the folks who measure such things:




    "I only ask that ALL things which can contribute to any warming be considered and not simply dismissed"

    Yeah, that's kind of why there is so much to learn. Because that's exactly what goes on - it's a big field of study, one that can't be summed up in an internet minute.
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  34. I thought these links (also added to the water vapor argument comments) would be useful given the comments above by BestTimesNow and Mizimi (namely that water vapor continually emitted by mankind from combustion or irrigation could serve as a forcing):

    The first is an atmospheric science PhD candidate's calculations regarding combustion-induced water vapor. His conclusion: the amount added from combustion is trivial.

    The second is a paper (Boucher 2004) that attempts to come up with a radiative forcing from global irrigation. Their conclusion: irrigation likely does add radiative forcing, but it is a trivial amount (0.03 to 0.1 W/M2) compared to atmospheric water vapor in general or C02- and the net climate effect is also likely much more complex than that given a strong cooling effect locally of irrigation (0.8 K locally), and vegetative changes that may affect albedo/C02 etc...

    I can't find much else out there on the topic, but thought these might be helpful to those wondering about "anthropogenic" water vapor.
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  35. At my institution full text of Boucher article is available, but not at home, so at this link at least the abstract can be gotten to.
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