"Bob" wrote in message
...
John Rumm wrote:

One of the things that interests me is why so little attention is paid to
water vapour. IIUC this is by far the most significant "greenhouse gas" -
and concentrations of that dwarf CO2 (man made or otherwise).

(the cynic might say that perhaps its because if you include it, you make
the man made CO2 component look far less significant, and that does not
suit the agenda!)


As I understand it, you are correct that water vapour is a greenhouse gas
and that its concentration is much higher than C02. However, being a
different molecule it has different characteristics regarding the
absorption and re-emission of infra red and so volume for volume has a
lower effect than CO2. Another factor is that its concentration in the
atmosphere is not *directly* affected by human activity but, since warmer
air can hold higher volumes of water vapour, its concentration can
indirectly be increased by warming that occurs for other reasons - for
example increasing CO2 concentration. So there is a kind of feedback
mechanism at play.

A very odd feedback mechanism..
if it were simple then the first hot day we have will result in more water
vapour..
leading to higher temps..
leading to more water vapour..
leading to the end of life as we know it Jim.

In summary, water vapour is indeed an important greenhouse gas but it is
not a 'driver' for the process of increasing the greenhouse effect.

So it isn't a feedback mechanism then?