Direct measurements of CO2 at Mauna Loa Observatory (“MLO”) in Hawaii began in March, 1958. That's the annual average CO2 concentration data graphed here for 1959 – 2022, downloaded from: https://www.esrl.noaa.gov/gmd/webdata/ccgg/trends/co2/co2_annmean_mlo.txt
NOAA's MLO monthly CO2 data can be downloaded here: https://www.esrl.noaa.gov/gmd/webdata/ccgg/trends/co2/co2_mm_mlo.txt. (You can also download the MLO monthly CO2 data in .json format here, or in .csv format here; it might be a day or two out-of-date.)
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 1780 as ≈280 ppmv, and 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 these spreadsheets, as well as from the Integrated Carbon Observation System (ICOS), and from ourworldindata (search the downloaded data file for “world”).
Last modified: 02-May-2023 (version 53)