Water Vapor, CO2, and Global Warming

In my discussions with people regarding climate change and global warming, I’ve found some confusion regarding the role that CO2 plays versus water vapor in the “greenhouse” effect.

In order to address this issue, I’ve done some further research on this particular aspect of greenhouse gasses, particularly citing the work and teaching of Dr. Richard Wolfson in the following comments.

As most people are aware, Earth’s climate would be considerably colder without the naturally occurring greenhouse effect – about 0 degrees Fahrenheit on average instead of the 58 to 60 degree average. The term greenhouse effect is a bit of a misnomer in that a greenhouse blocks heated air whereas the “greenhouse” gasses we discuss here are opaque to infrared radiation from the sun as it attempts to travel back into space off the Earth’s surface. Not quite the same thing as what actually happens in a greenhouse.

Nonetheless, the term has stuck, so we have greenhouse gasses creating the greenhouse effect. Water vapor is indeed the dominate atmospheric greenhouse gas for Earth’s natural greenhouse effect. Incidentally, this isn’t a secret that scientists are trying to keep from the public in order to promote their scare tactics and get grant money. As ludicrous as that statement sounds, I have heard such assertions in “debates” put forth in other forums as an argument denying climate change or CO2 buildup as a real concern.

In any case, even though water vapor is the predominate gas for the naturally occurring greenhouse effect, carbon dioxide plays a more important role in varying the strength of global warming.

The reason for this is due to the almost instantaneous adjustments of water vapor to changing conditions, cycling through the climate system normally in as little as a week. Carbon dioxide, on the other hand, sticks around in the atmosphere for decades. Thus, an increased input of CO2 into the atmosphere does not adjust to current conditions – it doesn’t rain liquid CO2. It builds up and thus drives the degree of global warming much more than water vapor.

To sum up, water vapor is indeed the dominate greenhouse gas involved in the naturally occurring greenhouse gas. Due to its quick adjustment to environmental changes in the atmosphere, it helps keep the energy balance of the climate system relatively stable. Carbon dioxide, while much less prevalent than water vapor, lingers in the atmosphere much, much longer (decades) and thus will steadily increase in atmospheric volume, altering the naturally occurring energy balance of the climate system. This is why CO2 has a greater role in determining the strength of the greenhouse effect


climate change global warming co2 carbon dioxide greenhouse gas greenhouse effect

Thomas Schueneman
Thomas Schuenemanhttps://tdsenvironmentalmedia.com
Tom is the founder and managing editor of GlobalWarmingisReal.com and the PlanetWatch Group. His work appears in Triple Pundit, Slate, Cleantechnia, Planetsave, Earth911, and several other sustainability-focused publications. Tom is a member of the Society of Environmental Journalists.

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  1. hello! i read your writing… i agree with you, i have this big debate coming up about what causes global warming… and thanks for clearing the questions by explaining the process straight to the point.

  2. You are correct that C02 will keep rising. But you have no evidence that it is a bad thing. And really when you look at the amount humans produce compared to the natural background it is minimal. C02 has been decreasing for years. When dinosaurs were around there was literally hundreds of times more. Put those figures into your computer programs and life would boil. And you say C02 hangs around in the atmosphere for years. LIKE CLOUDS DON’T! Jesus start thinking for your self and stop watching T.V. Thank you.

  3. John,

    Thanks for the comment. Try reading the post again or doing some more research.

    In any case the only thing I have the time to respond to here is the “LIKE CLOUDS DON’T” statement. John, do you really think that the water vapor making up a cloud you see this afternoon will be the same water vapor in the same cloud years from now?
    I agree we all need to think for ourselves. It starts with thinking.
    And you have an odd notion that you have any idea as to my television viewing habits.
    Nice try, but pretty weak. Feel free to try back anytime.

  4. The hotter the atmosphere, the more water vapor it can hold. So as industrial use of water goes up in parallel to carbon dioxide emission, water vapor has a positive feedback on global warming. This is accounted for in climate models, and I don’t think the role of water vapor is limited to local scales only (as opposed to global scale). The fact that water vapor can be recycled naturally into liquid water under normal climatic conditions helps to a certain extent, but does not deter from the fact that water vapor does have a global positive feedback on atmospheric warming.

  5. I agree with Colleen’s comments re your blog.

    I’ve been struggling for the past two weeks with the water vapor issue after reading an editorial by Patrick Betard in an automobile magazine. I couldn’t find anything on the web even relating to water vapor vs. COs until I found your site. Your article is a very good intro and simple answer to the Betard, and the infamous Mr. Heibs (apparently Betard’s source), challenges on water vapor.

    Their next challenge is that of the proportion of the industrial contribution of CO2 and the “natural” sources. Obviously they miss the point that any increase of CO2 left unchecked will eventually cause a problem.

    My question is, why haven’t all the other “pro global warming” sources, for a lack of a better term, addressed the water vapor issue? It does lead people like Heibs and Betard to accuse the supposed (in their minds) experts of hiding the importance of water vapor and thus lying. There are numerous articles on water vapor but they don’t clearly address the contection or relation to CO2.

    Clearly the consensus and data point to the impact of CO2. But without a good source of info it is difficult to answer the water vapor vs CO2 issue. Thanks for the clarity.

    I would greatly appreciate references to other discussions, papers or articles on the relation between water vapor and CO2 .

  6. David,

    Thanks for the comments. I understand your point about sources of climate change info not discussing water vapor. At first my impulse is to say that there must be many other sources discussing water vapor vs. CO2 in terms of global warming, but it sounds like you’ve just done some searching and landed here. Not that that is a bad thing, but let me find some more resources and I will either post them in another comment of do another post on the issue.

    Thanks for reading and discussing these issues.


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