[dirtbiker]

It's the second strongest greenhouse gas. Ozone is the third strongest. All the rest are also-rans. The water vapor that does the bulk of the warming would not be possible without CO2.

Ozone is NOT third, it is fourth.

The "greenhouse gases" are (in order and strength):
Water vapor 35-70%,
CO2 9-26% (I guess that depends on whether Algore is speaking that day),
Methane 4-9% (Depends on whether Big Al had a double chili burrito before speaking),
ozone 3-7% (Upper level ozone is produced by the sun)....

[palmer]

CO2 9-26% (I guess that depends on whether Algore is speaking that day),

Ranges depend on the spectral overlap. The issue of whether doubling CO2 causes catastrophic warming or not depends on that overlap plus the changes in weather that may occur at higher temperatures. Because of the overlap with H2O, the doubling of CO2 creates about a 0.25C temperature rise, not catastrophic. Factoring in weather changes, there may be a rise in the height of the troposphere or other changes that cause warming. Real world measurements are not conclusive but it is doubtful that there would be enough positive feedback to be considered catastrophic.