Eiron wrote:

How do scientists recognize 'new CO2'? Is it by the gauche manner of
the molecules? Their clumsy attempts at Brownian motion?


The increase in total atmospheric CO2 from 280 to 380 ppm over he last 150
years is well documented. The change in relative amounts of atmospheric 14C,
13C and 12C isotopes is also known. This, together with a knowledge of the
isotope mix in fossil fuels and some simple arithmetic, allows us to
identify the source of the extra CO2 as fossil fuels.

Data for the above comes from a variety of sources including entrapped air
in ice cores as well as C13/C12 isotope ratios from tree rings and corals.

There is also the simple fact that we have burned 500 billion metric tons of
carbon in the last 150 years. This is easily enough to have yielded the
observed increase in atmospheric CO2 even taking into account some
absorption by the biosphere and the oceans.

This is a quick summary....I'll provide further details if you want them.

The 'greenhouse effect' of CO2 is many times smaller than that of H2O
so Andre is right; it is pretty irrelevant.


Water vapor does act as a powerful greenhouse gas absorbing long-wave
radiation and contributes toward the already existing natural greenhouse
effect that makes life on earth possible at all. However, you have your
facts wrong about the relative effects of CO2 versus H2O. Wiki, for example,
puts the values at 60% for H2O, and 26% for CO2. So, the observed increase
in CO2 can and does have a significant effect on greenhouse warming.
Furthermore, any extra warming will cause water vapor levels to rise and so
we have the following positive feedback loop:

The greenhouse effect of carbon dioxide raises the temperature, and that
causes more water vapor to evaporate. The greenhouse effect of H2O then acts
as an amplifier of the CO2 effect, increasing the temperature further.
However, that increase in temperature causes more water vapor, and so the
water vapor is in a feedback loop with the surface/atmospheric temperature.
The water vapor effect is a feedback and the carbon dioxide effect is a
forcing in this particular loop (there are others).

Jo