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