True but it does provide a positive feedback effect, i.e. the hotter it gets, the more there is on average, and therefore the hotter it gets.
Its average concentration will only decrease if temperature decreases _first_ due to some stronger cooling effect. Such stronger cooling effects _do_ exist in nature, or we would never had had ice ages every 100000 years or so(*), but they are extremely slow in spite of the deceivingly abrupt-looking slopes (it takes about 5000 years to plunge into an ice age) so we shouldn't count on them to correct the comparatively instantaneous presently observed warming trend. Michel (*) Have those mechanisms been purely astronomical up to now (long term cyclical Earth orbit variations due to interactions with other planets) does anyone know? ----- Original Message ----- From: "Nick Palmer" <[EMAIL PROTECTED]> Sent: Friday, April 27, 2007 11:20 AM ... > P.S. Same thing for water vapour which is also "way more reactive" than > CO2 - it doesn't accumulate significantly because it precipitates out as > rain or snow and similarly it does not affect the upper atmosphere (any > vapour that gets up there changes into ice crystals)
