Born in 1999: CO2 then and now

In 1999 the air held 368.54 parts per million of CO₂, the annual mean measured at Mauna Loa.

In 2025, the latest complete year, the annual mean at Mauna Loa was 427.35 ppm: 16% more CO₂ in the air. Figures from the data files retrieved 16 October 2026.

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<a href="https://co2stats.com/co2/born-in/1999"><img src="https://co2stats.com/graphics/born-in-1999.svg" width="1200" height="630" alt="Born in 1999: 369 ppm of CO2 then (annual mean), 427 ppm in 2025 (annual mean), 16% more." style="max-width:100%;height:auto"></a>
<p>Graphic: <a href="https://co2stats.com/co2/born-in/1999">CO2Stats</a>, <a href="https://creativecommons.org/licenses/by/4.0/">CC BY 4.0</a>. Source: Dr. Xin Lan, NOAA/GML (gml.noaa.gov/ccgg/trends/) and Dr. Ralph Keeling, Scripps Institution of Oceanography (scrippsco2.ucsd.edu/). Data used under their sources' terms; no endorsement implied.</p>

Sources

Annual mean CO2, Mauna Loa Observatory, Hawaii. Dr. Xin Lan, NOAA/GML (gml.noaa.gov/ccgg/trends/) and Dr. Ralph Keeling, Scripps Institution of Oceanography (scrippsco2.ucsd.edu/). Retrieved 16 October 2026. Terms.

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