What do you want to compare about methane and CO2, Nad?

I don't know where the data in that particular graph came from, but this looks like a good place to find monthly averaged methane concentrations as measured at Mauna Loa:

* [Earth System Research Laboratory Global Monitoring Division - methane in situ monthly averages](http://www.esrl.noaa.gov/gmd/dv/data/index.php?site=mlo¶meter_name=Methane&pageID=2&frequency=Monthly%2BAverages).

This website has a lot of data.

In particular, [here](ftp://ftp.cmdl.noaa.gov/ccg/ch4/flask/month/ch4_mlo_surface-flask_1_ccgg_month.txt) is Ed Dlugokencky's data for monthly averages of methane concentrations from 1983 to 2011.

By the way - it's interesting to see that the concentration of methane in the air depends a lot on the latitude!

(Click for details.)