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Atmospheric Carbon Dioxide (CO2) levels, 1800–present

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Graph of atmospheric CO2 levels
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(hover mouse over options for detailed explanations)

All of the CO2 figures are annual averages.

To see precise values, hover your mouse cursor over the red graph trace. However, all values are shown with about one more significant digit than is warranted by the precision of the measurements, and the ice core values are much less accurate than the Mauna Loa Observatory (MLO) measurements.

We use Mauna Loa Observatory data because it has the longest high-quality measurement record. But CO2 levels are also measured in other places, such as Cape Grim[2], Tasmania (“CGO”), where CO2 levels average about 4 ppmv lower [spreadsheet], and the seasonal cycle is very different.

Click here for a downloadable, bookmarkable image (or use PrtScn).

The CO2level for the final year is a preliminary projection, estimated based on mid-summer values from the “de-seasonalized” column of NOAA's MLO monthly CO2 data.

We also have a similar graph for methane (CH4), and a combined graph with both CO2 and CH4.

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 – 2023, downloaded from: https://gml.noaa.gov/webdata/ccgg/trends/co2/co2_annmean_mlo.txt

NOAA's MLO monthly CO2 data can be downloaded here: https://gml.noaa.gov/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(You can also download the MLO monthly CO2 data in .json format here, or in .csv format here; it might be a day or two out-of-date.)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). (There are also CO2 records going back further, though with lower temporal resolution, from sites with slower ice accumulation rates: Vostok, Siple, EPICA Dome C, WAIS Divide, and composite.)

For a deeper dive into CO2 measurements from Antarctic and Greenland ice cores, I recommend these two articles by geologist Renee Hannon:
1. Hannon, R. (2024) Measurement of CO2 Concentrations Through Time Using Ice Core and Stomatal Proxy Data. CO2 Coalition.
2. Hannon, R. (2021) Greenland Ice Core CO2 during the past 1,000 years. Andy May Petrophysicist (blog).

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”).

 

SeaLevel.info

 

Last modified: 03-Feb-2025 (version 64)