Up-to-date weekly average CO₂ at Mauna Loa

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The graph, updated weekly, shows as individual points daily mean CO₂ up to and including the week (Sunday through Saturday) previous to today. The daily means are based on hours during which CO₂ was likely representative of “background” conditions, defined as times when the measurement is representative of air at mid-altitudes over the Pacific Ocean. That air has had several days time or more to mix, smoothing out most of the CO₂ variability encountered elsewhere, making the measurements representative of CO₂ over hundreds of km or more. The selection process is designed to filter out any influence of nearby emissions, or removals, of CO₂ such as caused by the vegetation on the island of Hawaii, and likewise emissions from the volcanic crater of Mauna Loa. For details, see ”How we measure background CO2 levels at Mauna Loa”. The same measurement principles also apply elsewhere. The weekly mean (red bar) is simply the average of all days in the week for which a background value could be defined. The average standard deviation of day to day variability, calculated as the difference from the appropriate weekly mean, equals 0.38 ppm for the entire record. As a visual aid, the blue lines present monthly means of background data as they are presented under Recent Monthly CO₂ at Mauna Loa.

These data are still preliminary, pending recalibrations of reference gases and other quality control checks.

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This figure shows the atmospheric increase of CO₂ over 280 ppm in weekly averages of CO₂ observed at Mauna Loa. The value of 280 ppm is chosen as representative of pre-industrial air because it is close to the average of CO₂ measured and dated with high time resolution between the years 1000 and 1800 in an ice core from Law Dome, Antarctica. [Etheridge et al., 1996]. Although the time resolution of old air locked in ice cores is not enough to preserve seasonal cycles, there is no doubt that the seasonal cycle, which is mostly caused by photosynthesis and respiration of ecosystems on land, was similar to what we observe today. Therefore, for the comparison with pre-industrial times the Mauna Loa weekly data have been first deseasonalized by subtracting the observed average seasonal cycle, and then subtracting 280 ppm. The enhancement of the CO₂ mole fraction in the atmosphere over pre-industrial is expressed both as ppm and as a percentage change since the year 1800.

Data are reported as a dry air mole fraction defined as the number of molecules of carbon dioxide divided by the number of all molecules in air, including CO₂ itself, after water vapor has been removed. The mole fraction is expressed as parts per million (ppm). Example: 0.000400 is expressed as 400 ppm.

Data

The Mauna Loa CO₂ data described on this page are available.

• Weekly mean CO₂ and historical comparisons

Further Reading

• Etheridge, D. M., L. P. Steele, R. L. Langenfelds, R. J. Francey, J.-M. Barnola, and V. I. Morgan, Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn, J. Geophys. Res., 101(D2), 4115–4128, doi:10.1029/95JD03410., 1996