In the discussion (Section 1.4) the composition of the Earth's atmosphere is reviewed and the dominant gasses contributing to atmospheric retention of thermal energy are noted. CO2 is the dominant contributor marked by a rise from 280 ppm (pre-industrial revolution) to the current (2019) level of 400 ppm. Water vapor is considered the second most significant contributor, followed by methane and nitrous oxide.
Based on the numbers presented in lecture, the relative effect
of methane to CO2 would be about 11% and that of nitrous oxide about 25%. I
wonder how water vapor concentrations vary through time. There are some nice
animations over the past 20 years but I haven't found any graphical
presentations of average annual water vapor concentrations.
I found an interesting series of plots obtained from the 2014 National Climate Assessment report that does illustrate changes in specific humidity going back to about 1970. All the data presented in the figure are headed in directions that will lead to increased atmospheric temperature.
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