Science Forums 2

[InfiniteNow]

Originally Posted by pmaust

Why is so much of the focus on Co2 when water vapor is a much more potent GH gas and there are thousands of times more of it put into the atmosphere every day?

The answer to your question is that water vapor is a feedback, not a forcing. CO₂, however, is a forcing.




This link goes into pretty good detail, and also helps raise your understanding on the issue quickly:

RealClimate » Water vapour: feedback or forcing?

While water vapour is indeed the most important greenhouse gas, the issue that makes it a feedback (rather than a forcing) is the relatively short residence time for water in the atmosphere (around 10 days).

<...>

Compared to the residence time for perturbations to CO₂ (decades to centuries) or CH₄ (a decade), this is a really short time.

When surface temperatures change (whether from CO₂ or solar forcing or volcanos etc.), you can therefore expect water vapour to adjust quickly to reflect that. To first approximation, the water vapour adjusts to maintain constant relative humidity. It's important to point out that this is a result of the models, not a built-in assumption. Since approximately constant relative humidity implies an increase in specific humidity for an increase in air temperatures, the total amount of water vapour will increase adding to the greenhouse trapping of long-wave radiation. This is the famed 'water vapour feedback'.

RealClimate » Water Vapour Feedback

One important difference between water vapour and other greenhouse gases such as CO₂ is that the moisture spends only a short time in the atmosphere before being precipitated out, whereas the life time of CO₂ in the atmosphere may be longer than 100 years.

Stoat: Water vapour is not the dominant greenhouse gas

So: adding CO₂ to the atmosphere warms it a bit and ends up with more [water vapor] WV. Adding WV does nothing much and the atmos returns to equilibrium. This is why WV is not the *dominant* [green house gas] GHG; its more like a submissive GHG.

Sorry to hear about your hand. Maybe you can learn to type with your toes?


All the best.