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Answer: Atmospheric carbon dioxide keeps rising because human activities release more each year than natural processes can remove. The global average set a record of 422.7 parts per million (ppm) in 2024, and the recent rate of increase is about 100 times faster than natural increases such as the end of the last ice age.

The Mauna Loa record

The modern record began with measurements at Mauna Loa Observatory in Hawaii in 1958. NOAA's Global Monitoring Laboratory publishes the monthly means, combining Scripps and NOAA data. The yearly sawtooth comes from Northern Hemisphere plants taking up carbon in summer and releasing it in winter.

When the Mauna Loa volcano erupted in late 2022, measurements were moved temporarily to a site at the Maunakea Observatories, about 21 miles north, and resumed at Mauna Loa in July 2023.

Units

Concentration is reported as a mole fraction in dry air, in ppm: the number of CO2 molecules per million molecules of air after water vapor is removed.

Ocean link

The ocean has absorbed enough CO2 to lower its pH by about 0.1 units, roughly a 30 percent increase in acidity.

Claims

• id: C1 claim: Human activities release more carbon dioxide than natural processes can remove. source: S1 evidence: "human activities release more carbon dioxide into the atmosphere than natural processes can remove"
• id: C2 claim: Global average carbon dioxide set a record of 422.7 ppm in 2024. source: S1 evidence: "The global average carbon dioxide set a new record high in 2024: 422.7 parts per"
• id: C3 claim: Ocean CO2 uptake lowered pH by 0.1 units. source: S1 evidence: "The ocean has absorbed enough carbon dioxide to lower its pH by 0.1 units"
• id: C4 claim: The graphs show monthly mean CO2 measured at Mauna Loa. source: S2 evidence: "The graphs show monthly mean carbon dioxide measured at Mauna Loa Observatory, Hawaii."
• id: C5 claim: Mauna Loa observations resumed in July 2023. source: S2 evidence: "Mauna Loa observations resumed in July 2023."

Sources

• [S1] Climate change: atmospheric carbon dioxide. NOAA. https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide . License: US government work, public domain. Accessed 2026-11-04.
• [S2] Trends in CO2 - NOAA Global Monitoring Laboratory. NOAA. https://gml.noaa.gov/ccgg/trends/ . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_twhqfqn9,
  author = {{iinventedlight}},
  title = {{Atmospheric carbon dioxide trends}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/carbon-dioxide-trends/},
  note = {Permanent ID iil:note:twhqfqn9. License: CC-BY-4.0.},
}

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