CFC-11 and CFC-12 are very potent greenhouse gases. Suppose the emission of 1 Tg of CFC-11 causes a 1.0 W m-2 instantaneous perturbation in the radiation budget. The emission of the 1 Tg of CFC-12 causes a 1.5 W m-2 radiative forcing.

Question

The 100 year global warming potential for CFC-11 is estimated to be 4750. Global warming potential is a measure of how much energy would be trapped by the emission of one molecule of a given gas over a specified time period, in this case 100 years, relative to CO2. Global warming potential depends on both the atmospheric lifetime of a gas, as well as its ability to absorb infra-red radiation.

Use the information on the lifetimes and relative radiative forcing strengths of CFC-11 and CFC-12, as well as the global warming potential of CFC-11 to estimate the global warming potential of CFC-12. You may assume that the radiative forcing of each species is simply proportional to its concentration.

Hint: Use the model from part (a) to calculate the total energy absorbed by the instantaneous injection of 1 Tg of each CFC into the atmosphere over 100 years. The ratio of these two energies is the ratio of the global warming potentials.

Answer 1

Model from Part (a) is

dC/dt = E - (C/tau)
C - concentration of the gas [Tg]
E - emission rate [Tg/yr]
t - time [yr]
tau - represents the lifetime of the gas in the atmosphere, before it is removed, either by chemical reactions or deposition to the surface [yr]