A Few Things Ill Considered

Climate Scientists Hide Water Vapor

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.


Objection:

Climate scientists never talk about water vapor, which is the strongest greenhouse gas, because it undermines their CO2 theory.

Answer:

There is no climate model or climate textbook that does not discuss the role water vapor plays in the Greenhouse Effect. It is the strongest Greenhouse gas, contributing 36% – 66% to the overall effect for vapor alone, 66% to 85% when you include clouds. It is however, not considered as a climate "forcing" because the amount of H2O in the air basically varies as a function of temperature. If you artificially increase the level of H2O in the air, it rains out immediately (in terms of climate response times). Similarly, due to the abundance of ocean on the Earth’s surface, if you somehow removed all the water from the air it would quickly be replaced through evaporation. This has the interesting consequence that if one could somehow instantly remove all CO2 from the atmosphere, the temperature would begin to drop, causing precipitation to remove H2O from the air causing even further drops, in a feedback effect that would not end until no liquid water was left, only ice sheets and frozen oceans.

CO2 put into the air by burning fossil fuels, on the other hand, has an atmospheric lifetime of centuries before natural sinks will finish absorbing any excess from the air. This is plenty of time to have substantial and long lasting effects on the climate system. As the climate warms in response to the CO2, the humidity rises and the increased H2O concentration acts as a significant amplifier of CO2 driven warming, basically doubling or tripling its effect.

This article from Real Climate has an good discussion of this: "Water vapor, forcing or feedback?"


This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.


“Climate Scientists Hide Water Vapor” was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.

Comments

  1. #1 Bob
    March 3, 2009

    I have been studying the global warming arguments for a few years and watch the current discussions with interest. It now appears we are in a global cooling phase. The Warmaholics seem to be averting their eyes from this twelve-year-old development. Even leaving solar effects out of the discussion your math does not hold up. CO2 does not appear to be a significant issue. I suggest you get your grant requests approved while you still can. You are losing the argument.

  2. #2 Adam
    March 3, 2009

    One cool year (relative to the past few years, not the historical record) does not make a “global cooling phase.”

    “12-year-development”
    The 10 warmest years on record have all occurred between 1997 and 2008, so I’m not sure what you’re basing this assertion on. Unless you’re arbitrarily claiming the hottest year you can find as the baseline, and saying the temperature decreasing since then, which is, at best, dishonest.

  3. #3 coby
    March 3, 2009

    Bob, when cherry picking, it is essential to pick the right one! 12 years ago the temperature was cooler than today, so global warming is happening. You need to say 11 years ago, then global cooling is happening.

    HTH!

    (BTW, check here for why that reasoning is bunk)

  4. #4 MattBennett
    March 4, 2009

    “I have been studying the global warming arguments for a few years”…….

    If you’re still being fooled by something as pedestrian as the mis-use of statistics behind ‘global cooling’ claims, I’d recommend you refrain from using such sentences and pretend you’re new to this.

  5. #5 vernon
    March 4, 2009

    What about the new study by NCEP, Paltridge, Arking, and Pook (2009) Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data which found that upper tropospheric humidity was decreasing and that would make water vapor a negative forcing? Admittedly additional work needs to be done, but if this is proven true, does not that invalidate all the current climate models?

  6. #6 coby
    March 4, 2009

    Hi vernon,

    If this finding, which is inconsistent with satellite observations as well, btw, holds up, it would certainly beg for an explanation.

    I presume by “invalidate the models” you mean cast doubt on long term projections and climate sensitivity to CO2? Because these models are very large and complex, so finding a facet that needs improvement is not fairly characterized by “invalidated”. “All models are wrong, but some are useful” so they say.

    Don’t forget that climate sensitivity to CO2 is also constrained by historical observations, not just model output and theory.

    But I reiterate: if that finding turns out to be robust, it will certainly want explaining and I am sure will be investigated.

    Thanks for the question!

  7. #7 John
    March 4, 2009

    Hello coby – I wanted to click on “this finding” in your comment but it doesn’t seem to be URL enabled (clickable). Can you provide the link? Cheers.

  8. #8 Vernon
    March 5, 2009

    Sorry, I express myself poorly at times. Invalidate may have been too strong a word to use. What I ment was that water vapor is a positive forcing in all the models and if that changes, what impact does it have on the modeling? My understanding is that H2O has a positive feedback (I think I read that it doubled the impact of pure CO2 warming) and the new study indicates that it is a negative feed back (effectively halfing the impact of pure CO2 warming). What does that do to the models?

  9. #9 coby
    March 5, 2009

    Vernon, the link is fixed, sorry! I is just to the abstract of the study you are referring to. I think it is a localized finding, and as such, and if it holds up, it may well have a localized explanation. After all, warmer air holding more humidity is very basic stuff, and it’s next to impossible that that basic fact will be falsified. If humidity is not rising as expected in the tropical upper atmosphere, then there is likely something missing from the models as well as the theoretical picture.

    For me personally, the best reason to have some confidence in model projections of the next century is their skill at hindcasting the 20th century.

  10. #10 crakar14
    May 11, 2009

    Coby i am a bit confused, first you make this statement

    “If you artificially increase the level of H2O in the air, it rains out immediately (in terms of climate response times). Similarly, due to the abundance of ocean on the Earth’s surface, if you somehow removed all the water from the air it would quickly be replaced through evaporation”

    Infering that it is not a forcing and only increases in CO2 can have any affects on temp changes.

    [Any forcing would create an H2O feedback, not just CO2. There are many factors that can affect temperature.
    – coby]

    Then you say this “As the climate warms in response to the CO2, the humidity rises and the increased H2O concentration acts as a significant amplifier of CO2 driven warming, basically doubling or tripling its effect.”

    Would the H2O simply rain out immediately like before? This all made sense when i stumbled across this article

    http://www.geocraft.com/WVFossils/greenhouse_data.html

    [In the first hypothetical example, H2O is artificially increased. In the second it increases as a response to warming: warmer air holds more water. So no, it behaves differently.
    – coby]

    This explains why people like you dismiss water vapour out of hand when i suits. The con game is coming to an end.

  11. #11 Chris
    May 11, 2009

    “For me personally, the best reason to have some confidence in model projections of the next century is their skill at hindcasting the 20th century.”

    Coby… The ‘hindcasts’ are nothing but curve fitting exercises. The GCMs have what… ten variables? Twenty? More than enough to get any sort of curve you want by tweaking some numbers here and there, all within the range of ‘somewhat realistic.’ Hindcasting does not impress me one bit. History is full of ‘hindcasts’ that seemed to work perfectly. Most are economic models, though I’m sure there are others as well. But when it came time to apply the models that hindcast so very well to the FUTURE, something interesting happened. They were wrong. Some less, some more, some disastrously so. But all of them were wrong. Hindcasting proves absolutely nothing. Show me a model that works FORWARD as well as backward, and then we can have talks about ‘confidence.’

  12. #12 ThomasC
    June 15, 2009

    Coby, hi. Long time lurker, first time poster.

    Coby: “Please see this [points to here] article. Water vapour is the strongest GHG in the atmosphere but it does not act as a forcing due to the fact that as a general approximation relative humidity remains constant as temperatures go up or down.”

    This was taken from another thread on LIA. I’m not sure I follow your statement about constant relative humidity and it’s effects of forcing, could you explain? Constant relative humidity at different temperatures simply states that there is more kg_H2O per kg_air at the higher temperature (higher humidity ratio). Is it correct to assume that a higher humidity ratio is the main (only?) parameter with regards to VW’s share of longwave-IR absorption? It seems that higher HR will absorb more longwave-IR, causing the misleadingly-named Greenhouse Effect.

    So why can’t WV be a better forcing than CO2, assuming an increased WV content as an effect of a weak driver? Especially considering that WV seems to dominate the entire absorption spectrum (Ref. http://en.wikipedia.org/wiki/File:Atmospheric_Transmission.png ) ?

  13. #13 Mark
    December 5, 2009

    I have a sincere question: if global warming means that more water vapor will be in the atmosphere due to the feedback effect described above, won’t that at least partially offset the rise in sea levels due to melting ice? The water has to come from somewhere, right, and ultimately that will be the seas, since most water on earth is in the seas. I assume the models of sea level change take this into account, so am I right to assume that the decrease in sea levels associated with more water in the atmosphere is tiny compared to the increase caused by melting ice?

  14. #14 coby
    December 6, 2009

    Hi Mark,

    Sorry I don’t have numbers or a reference for you but I know I have seen discussions with numbers about exactly this question. You are right that the extra water held by the atmosphere will reduce the water in the ocean, but the amount is negligible (mm’s) compared to the rise over the century expected from thermal expansion and glaciers (30-80cm) and from ice sheet melting (.5m?, 1m?, 2m? who knows right now)

  15. #15 Denis
    February 14, 2010

    “One cool year ….”

    Jones, of Anglia /Hadley fame has admitted that there has been no warming since 1995. (Others claim that the past 8 years have been cooler).

    The difference in “measurements” betwixt which is hottest, and the neighboring candidates, are usually so close that there is no real distinction; differences are often in the “noise”level. At one point 1934 was hottest years, but the “scientists” revisited and instead awarded the prize to a very recent year. As I recall the difference was perhaps 1/10 of a degree.) The “homogenizing” makes crude estimates of UHI for older data that may be off (sometimes by purpose, evidently) by several degrees. How can anyone possibly declare, with a straight face, which year (or day) is hottest or coolest when other candidates (years or days) are that close?

  16. #16 Wow
    March 22, 2011

    Which you can do by buying a pool, #16?!?!?

    Spamalot.

  17. #17 blueshift
    March 22, 2011

    Denis #15,

    You are repeating nonsense.

    First, Jones said that we couldn’t say with 95% confidence that the warming was distinguishable from random variation.

    Second 1934 was the warmest for the USA only, not the world.

    I suspect that you have been misled by someone instead of personally reviewing the issues. So I suggest you don’t take my word for it but go to the source, see what was actually said or done and then re-examine who you trust on these issues.

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