On 29/05/07, Rob Jacob <[EMAIL PROTECTED]> wrote:
>
> Water vapor is a stronger greenhouse gas and has
> a larger concentration but there's very little we can do to change its
> concentration. Except indirectly. And this is where CO2 comes in
> again. The CO2-induced temperature increase allows the atmosphere to
> hold more water vapor which leads to another temperature increase.
> But the root cause is CO2.
This is the basic "forcing" vs. "feedback" distinction.
The CO2 that we put into the atmosphere - that is the forcing, the
water vapor is the feedback. The forcing is the input, and what
results is feedback - until equilibrium is re-established.
Anyway, the big problem with CO2 is that it stays in the atmosphere
for a very long time - I believe about twenty percent of what we put
out will stay up there for at least a century - although I would have
to check the figures. In contrast, water vapor stays up there pretty
much until the next time it rains. So its not just a matter of our
putting it up there, but it staying up there and affecting the climate
over an extended period of time - slowing the rate at which thermal
energy can be dissipated into space until the temperature of the earth
rises enough that the thermal energy it radiates is equal to the
amount of thermal energy entering the system.
But the rise in temperature causes more water to evaporate, then the
feedback - which results in the equilibrium being push out a little
further, Ultimately, the final equilibrium is a result of positive
and negative feedback involving radiation, albedo (clouds, ice and
snow), CO2, water vapor, temperature and convection.
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