NOAA Monthly CO2 PPM

This dataset has the average monthly carbon dioxide parts per million observed at the Mauna Loa Observatory in Hawaii. The observations started in 1958 and continues monthly.

The Mauna Loa Observatory (MLO) is an atmospheric baseline station of the Global Monitoring Laboratory (GML), of the National Oceanic and Atmospheric Administration (NOAA). The mission of ESRL is to measure atmospheric constituents that are capable of forcing change in the climate of the earth and those that may deplete the ozone layer. ESRL accomplishes this goal primarily through long-term tropospheric measurements of key atmospheric parameters such as carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), chlorofluorocarbons (CFCs), ozone (O3), sulfur dioxide (SO2), nitrous oxide (N2O), radon, aerosols, optical depth, and a spectrum of solar radiation parameters.
https://gml.noaa.gov/obop/mlo/aboutus/aboutus.html