Supposedly this OLR portion of earth's outgoing spectrum is curtailed by greenhouse gas "heat trapping" and should go down. Instead the opposite is found.
Basically OLR follows earth's average air temps as you'd expect and there is no CO2-related "heat trapping" evident.
I took NCEP reanalysis of OLR at nominal top of atmosphere and made the following graph by averaging all values for latitude and longitude in the NetCDF file I downloaded.
I used some summing funtions in Matlab – a program I'm not that familiar with so I hope I got it right. The value and shape of waveform looks about right so I think so.
I don't how they determine the values from the year 1948 onward given the satellite era only starts in 1979 (or thereabouts). Anyway, here it is along with HadCru version 3 global temps:
|Outgoing Longwave radiation from nominal top of atmosphere and Hadcru global average temperature|