This question is not about man-made global warming, but about the total greenhouse effect.

According to http://www.geocraft.com/WVFossils/greenhouse_data.html , 95% of the greenhouse effect is due to water vapor (gas phase H2O). It cites to references 5a-5h.

On the other hand, the American Chemical Society says 60% is the correct value, but doesn't cite any references.

What is the correct value for water vapor's contribution to the total effect of all greenhouse gases?

  • 1
    The supposed source for that 95% figure is the very rarely referenced article Solar radiation absorption by CO2, overlap with H2O, and a parameterization for general circulation models. This article has been referenced 8 times in the last 24 years. The low citation rate means two things: (1) I have to pay to see the article, and (2) I don't want to pay to see the article. Dec 10, 2016 at 23:42
  • That said, I truly doubt the article said what the first link claims it said. The abstract to that article says "A broadband parameterization for CO2 absorption, employed in several weather prediction and climate models, is found to substantially underestimate the LBL heating rates throughout the atmosphere, most notably in the stratosphere." It would take a serious misreading to get past that to claim that almost all of the greenhouse effect is due to water vapor. Dec 10, 2016 at 23:47
  • 1
    This gets to one of the key reasons I only frequently participate in this site. It is so easy to create fake scientific news. Simply site an old article that is infrequently referenced as the basis for whatever claim you want to make. The article should be at least 20 years old and should be rarely cited. With that, the odds are you can get away with your lie. The article will not be freely available on the web. No one is going to pay the extravagant fee to read that old article, and if someone does so, the fake news authors will find a way to weasel-word their way around their claim. Dec 11, 2016 at 0:11
  • 2
    Any article from Energy and Environment is suspect. That journal regularly touts articles that are the moral equivalent of "Smoking tobacco is good for you. Here! Have a drag!" Dec 11, 2016 at 2:08
  • 1
    In other words, if you include "intentionally lying" as one of your factors (thanks, @PoloHoleSet), it's easy to make this claim. Here's the recipe: Use one rarely cited technical article that doesn't support your claim, use some more "personal communications" (who knows why those said), use a few articles from known excrement sources, and just for funsies, toss in a reference or two to sites that right up front says they're bogus news sources. Voila! You have a completely false claim that appears to be well researched. Dec 12, 2016 at 18:51

1 Answer 1


No, more like 50%, at least according to this study:

Attribution of the present‐day total greenhouse effect

Gavin A. Schmidt, Reto A. Ruedy,Ron L. Miller and Andy A. Lacis

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, D20106, doi:10.1029/2010JD014287 , 2010


The relative contributions of atmospheric long‐wave absorbers to the present‐day global greenhouse effect are among the most misquoted statistics in public discussions of climate change. Much of the interest in these values is however due to an implicit assumption that these contributions are directly relevant for the question of climate sensitivity. Motivated by the need for a clear reference for this issue, we review the existing literature and use the Goddard Institute for Space Studies ModelE radiation module to provide an overview of the role of each absorber at the present‐day and under doubled CO2. With a straightforward scheme for allocating overlaps, we find that water vapor is the dominant contributor (∼50% of the effect), followed by clouds (∼25%) and then CO2 with ∼20%. All other absorbers play only minor roles. In a doubled CO2 scenario, this allocation is essentially unchanged, even though the magnitude of the total greenhouse effect is significantly larger than the initial radiative forcing, underscoring the importance of feedbacks from water vapor and clouds to climate sensitivity.

.pdf here. See also the RealClimate article (written by Gavin Schmidt) here, which explains why the overlap in absorbtion makes the definition of the contribution of each gas difficult to define unambiguously, but the range of definitions mean that:

... it’s clear that water vapour is the single most important absorber (between 36% and 66% of the greenhouse effect), and together with clouds makes up between 66% and 85%. CO2 alone makes up between 9 and 26%, while the O3 and the other minor GHG absorbers consist of up to 7 and 8% of the effect, respectively.

Note that water vapour acts as a positive feedback because it is a condensing greenhouse gas (GHG) rather than a long-lived one, i.e. it doesn't accumulate in the atmosphere like CO2 does, as the amount of water vapour the atmosphere can hold depends on its temperature (Clausius-Clapeyron) so if excess water vapour is injected into the atmosphere, it quickly precipitates out again as rain/snow. Thus it is the CO2 that is responsible for the bulk of climate change, exacerbated by the positive feedback from the concomitant increase in water vapour.

  • So reference is saying 50% gas phase h2o and 25% solid and liquid h2o (clouds), but is that percent just based on outgoing radiation blocked, or net warming considering that the clouds block incoming light also?
    – DavePhD
    Dec 10, 2016 at 16:53
  • It's my question, and it say "What is the correct value for water vapor's contribution to the total effect of all greenhouse gases?". I like your answer +1 thank you
    – DavePhD
    Dec 10, 2016 at 17:16

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