Question 1 page 37.
A. Is 10 additional ppm of methane in the atmosphere more or less important than 10 additional
ppm of CO2 in the atmosphere at current concentrations?
At default conditions, the intensity going out is 287.844 and the ground Temperature in Kelvin
should = 299.70. If the CO2 concentration is increased by 10 ppm, the intensity going out
decreases by ~0.1 to 287.75, and the temperature stays the same, oddly. If the methane
concentration is increased by 10, which is almost a 10-fold increase, the intensity going out falls
to 285.75, while the temperature again stays the same (malfunction? It should increase as the
intensity of escaping light decreases, right?)
B. Where in the spectrum does methane absorb? What concentration would it take to begin to
saturate the absorption in this band? (How do you identify saturation of a band on a spectrum
plot?)
Methane seems to absorb the wavelength around 1300 cycles/cm. However, as the
concentration increases (to an extreme degree), the areas around 1300, 1100 and 1400,
decrease much more. At a saturation of 100 ppm, you can clearly see the methane wavelength,
and at 1000 ppm, the wavelength appears to be near-saturated, with a very clear and smooth
line in that band.
C. Would a doubling of methane have as great an impact on the heat balance as a doubling of
CO2?
Doubling the methane concentration decreased the outgoing light intensity by 0.75, whereas
doubling the CO2 concentration decreased it by more than 3! CO2 being doubled wout have a
much greater impact.
D. What is the “equivalent CO2” of doubling atmospheric methane? That is to say, how many ppm
of CO2 would lead to the same change in outgoing IR radiation energy flux as doubling
methane? What is the ratio of ppm CO2 change to ppm methane change?
An increase of 68 ppm CO2 equaled the change in intensity caused by doubling the methane. An
increase of 175 ppm CO2 equaled the change caused by quadrupling the methane. From this,
we can conclude that ~60 ppm of CO2 is equivalent to 1.7 ppm of methane. That means that a
change of 35 ppm CO2 should be equivalent to 1 ppm of methane.