To see precise values, hover your mouse cursor over the red and blue graph traces. (However, the ice core values are less accurate than the Mauna Loa measurements.)
The relative scaling of the CO2 and CH4 axes was chosen so that the relative visual magnitude of changes in the two traces would approximate the relative warming effect of changes in the levels of the two gases. Additional CH4 is variously estimated to have between 25x and 35x the warming effect of the same amount of additional CO2; we used 25:1 so that the grid lines would line up nicely in the graph. However, the absolute height of the CH4 trace in this graph, relative to the bottom of the graph, still greatly exaggerates its total warming affect, compared to CO2.
1850-1958 CO2 data is from http://data.giss.nasa.gov/modelforce/ghgases/Fig1A.ext.txt (ice cores).
1958-present CO2 data is from ftp://aftp.cmdl.noaa.gov/products/trends/co2/co2_annmean_mlo.txt (measurements at Mauna Loa Observatory, HI).
1850-1992 CH4 data is from http://cdiac.ornl.gov/ftp/trends/atm_meth/EthCH498B.txt (ice cores), interpolated.
1984-present CH4 data is from ftp://aftp.cmdl.noaa.gov/products/trends/ch4/ch4_annmean_gl.txt (measurements at Mauna Loa).
We also have individual graphs of carbon dioxide (CO2) and methane (CH4) levels.