Direct measurements of CO2 at Mauna Loa Observatory (“MLO”) in Hawaii began in March, 1958. This is the annual average data graphed here (for 1959–2021):
ftp://aftp.cmdl.noaa.gov/products/trends/co2/co2_annmean_mlo.txt or https://www.esrl.noaa.gov/gmd/webdata/ccgg/trends/co2/co2_annmean_mlo.txt
For monthly data see:
ftp://aftp.cmdl.noaa.gov/products/trends/co2/co2_mm_mlo.txt or https://www.esrl.noaa.gov/gmd/webdata/ccgg/trends/co2/co2_mm_mlo.txt.
1850-1958 data is from http://data.giss.nasa.gov/modelforce/ghgases/Fig1A.ext.txt (ice cores).
1800-1850 CO2 data is from https://www1.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/law/law_co2.txt (Law Dome ice cores, 75 year smoothed; it also estimates CO2 in 1750 as ≈277 ppmv).
For a deeper dive into CO2 measurements from Antarctic and Greenland ice cores, I recommend this article by geologist Renee Hannon.
Historical “carbon budget” information, about sources, sinks & fluxes of CO2 since 1750 can be found in this spreadsheet (or as .xlsx), and newer data is available from the Integrated Carbon Observation System (ICOS), and from ourworldindata (search the downloaded data file for “world”).
Last modified: 22-Mar-2022 (version 43)