banner: annual CO2 levels for the past 3 years


Annual CO2

Atmospheric CO2 Levels
Mauna Loa Observatory (MLO) & Global


MLO (*)



421.08 420.78 2023 TBD
418.53 418.22 2022 417.07
416.41 416.11 2021 414.70
414.21 413.95 2020 412.44
411.65 411.42 2019 410.07
408.72 408.53 2018 407.61
406.76 406.52 2017 405.22
Feb. 5, 2024
Jan. 8, 2024
latest update
Feb. 5, 2023
.txt + web
.csv + web (*)
source datasets
.txt + web

annual mean concentrations  |  ppm = parts per million

* Annual values for Scripps are calculated by CO2.Earth as a
12-month average of the Scripps monthly mean concentrations.


The direction of atmospheric CO2 has been constant for decades.  Year after year since 1958 when Charles David Keeling started measurements at the Mauna Loa Observatory in Hawaii, earth's background CO2 level has only gone up.   Overall, the increases have been accelerating.

The Mauna Loa Observatory is home to two independent CO2 monitoring programs:

  • April 1974 - Present  Global Monitoring Division | National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL)
  • 1958 - Present  Scripps CO2 Program | Scripps Institution of Oceanography (SIO) at the University of California San Diego (UCSD)

NOAA operates the Mauna Loa facility.


Citing the Current Global Average


Two common ways exist for citing current global average concentrations of CO2 in the atmosphere.  One uses the annual average concentration measured at one location, the Mauna Loa Observatory (MLO).  The other uses an annual 'spatial' average of globally-averaged marine surface data from the NOAA-ESRL cooperative air sampling network.  The MLO average is considered a good approximation although the data above shows that it is typically about 1.4 ppm aove the spaial average. (Citing global averages is discussed by T.J. Blasing at footnote 7 of the CDIAC update for recent GHG concentrations.)