Retief wrote:


They absorb at different wavelengths, and they absorb at different
efficiencies. No, they are not similar.


Stepping in with a boring physics point this is actually very
important.

Any greenhouse gas operates by absorbing certain wavelengths more than
others - as the concentration of the gas increases so does absorbtion
but this is not and can not be linear. There is a law of diminishing
returns.

To see why take a simple example.
Gas x at concentration c absorbs 60% of frequency y - being a
relatively long wavelength this is primarily in the form of heat
radiated from the ground and so gas x is a strong greenhouse gas.
If we double the concentrations of gas x to 2c it cannot absorb 120% of
the frequency y (that would be nonsense) nor can it start absorbing
neighbouring frequencies (that defies the very physics that are
occurring). In practice the total absorbtion would tend towards 100% of
the specific frequencies at which point further concentrations have no
further forcing effect on climate change.

One of the reasons why this matters is that a mix of greenhouse gasses
has a far greater capacity to warm than a single gas. Doubling a single
gas is NOT the same as leaving that gas unchanged and adding a
supposedly equivalent amount of a different gas - the two gasses will
have a greater warming effect than twice the amount of a single gas for
any case where the warming effect is significant.


The sun behaves approximately as a black body. If the sun increases
in temperature (and output), the spectrum shifts towards the blue (and
increased UV).


It is probably more relevant that we are within the suns magnetosphere
and the effects that has on our climate are still rather poorly
understood, probably in part because climatologists are not solar
physicists by trade or training. In a sense the Earth is inside the
Sun's outer atmosphere and is directly affected by fluctuations in that
atmosphere.

--
Nic