Mauna Loa CO₂ tracker
Carbon dioxide at NOAA's Mauna Loa Observatory averaged 426.07 parts per million (ppm) in September 2026, up 1.70 ppm from September 2025. This page tracks the monthly record that began in March 1958.
Updated 27 October 2026. Source: NOAA Global Monitoring Laboratory (Mauna Loa Observatory).
Monthly mean CO₂ at Mauna Loa, last 24 months
| Month | Monthly mean (ppm) | Seasonally adjusted (ppm) | Change vs a year earlier (ppm) |
|---|---|---|---|
| September 2026 | 426.07 | 429.55 | +1.70 |
| August 2026 | 427.55 | 429.48 | +2.07 |
| July 2026 | 429.13 | 428.74 | +1.26 |
| June 2026 | 431.43 | 429.00 | +1.82 |
| May 2026 | 432.34 | 429.05 | +1.83 |
| April 2026 | 431.12 | 428.60 | +1.48 |
| March 2026 | 430.15 | 428.69 | +2.00 |
| February 2026 | 429.35 | 428.39 | +2.26 |
| January 2026 | 428.62 | 428.32 | +1.97 |
| December 2025 | 427.49 | 428.22 | +2.09 |
| November 2025 | 426.46 | 428.40 | +2.61 |
| October 2025 | 424.87 | 428.12 | +2.49 |
| September 2025 | 424.37 | 427.85 | +2.34 |
| August 2025 | 425.48 | 427.41 | +2.49 |
| July 2025 | 427.87 | 427.49 | +2.32 |
| June 2025 | 429.61 | 427.18 | +2.70 |
| May 2025 | 430.51 | 427.22 | +3.61 |
| April 2025 | 429.64 | 427.12 | +3.13 |
| March 2025 | 428.15 | 426.69 | +2.77 |
| February 2025 | 427.09 | 426.12 | +2.54 |
| January 2025 | 426.65 | 426.36 | +3.85 |
| December 2024 | 425.40 | 426.14 | +3.54 |
| November 2024 | 423.85 | 425.80 | +3.39 |
| October 2024 | 422.38 | 425.63 | +3.56 |
About the data
The figures are monthly means of carbon dioxide measured continuously at Mauna Loa Observatory, Hawaii, published by the NOAA Global Monitoring Laboratory. The Mauna Loa record, started by Charles David Keeling of the Scripps Institution of Oceanography in 1958, is the longest continuous direct record of atmospheric CO₂.
The seasonally adjusted column removes the regular yearly cycle, in which CO₂ falls during the Northern Hemisphere growing season and rises again in autumn and winter. Comparing a month with the same month a year earlier is the simplest way to see the underlying trend.
NOAA treats the latest year of data as preliminary, pending recalibration, so recent values can change. After the 2022 eruption of Mauna Loa, observations from December 2022 to early July 2023 came from a site at the Maunakea Observatories about 21 miles to the north. This page reflects NOAA’s latest published file and is refreshed daily; the average yearly rise is calculated by HalcyonWire from complete calendar-year means.
Suggested source citation: NOAA Global Monitoring Laboratory, Mauna Loa monthly mean CO₂ (gml.noaa.gov/ccgg/trends/); March 1958 to April 1974 data by C. David Keeling, Scripps Institution of Oceanography (scrippsco2.ucsd.edu).
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