Atmospheric carbon dioxide concentrations are needed as input into many environmental simulation models. These concentrations will change in the future in response to changing emissions of carbon dioxide and changing land use. Scenarios of future carbon dioxide concentrations can be obtained from the DDC from the GCM Experiments page.
Here, we provide measurements of atmospheric carbon dioxide concentration over the baseline period from 1961 to 1990. These data are taken from the Mauna Loa record (Hawaii, 19º32'N, 3397 m above sea level), the longest continuous record of atmospheric carbon dioxide for anywhere in the world. The Mauna Loa site is considered one of the most favourable locations for measuring undisturbed air because possible local influences of vegetation or human activities on atmospheric carbon dioxide concentrations are minimal and any influences from volcanic vents may be excluded from the records. The methods and equipment used to obtain these measurements have remained essentially unchanged during the 40-year record.
Because of the favourable site location, continuous monitoring, and careful selection and scrutiny of the data, the Mauna Loa record is considered to be a precise record and a reliable indicator of the regional trend in the concentration of atmospheric carbon dioxide in the middle layers of the troposphere. The Mauna Loa record shows a 14.8% increase in the mean annual concentration from 315.83 parts per million by volume (ppmv) of dry air in 1959 to 362.57 ppmv in 1996. The full dataset and further description of the Mauna Loa record can be obtained from the CDIAC data file.
Annual-mean atmospheric carbon dioxide concentrations (ppmv) for Mauna
Loa
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | Ave. | |
| 1950 | - | - | - | - | - | - | - | - | - | 315.8 | - |
| 1960 | 316.7 | 317.5 | 318.3 | 318.8 | 319.4 | 319.9 | 321.2 | 322.0 | 322.9 | 324.5 | 320.1 |
| 1970 | 325.5 | 326.2 | 327.3 | 329.5 | 330.1 | 331.0 | 332.0 | 333.7 | 335.3 | 336.7 | 330.7 |
| 1980 | 338.5 | 339.8 | 342.0 | 342.6 | 344.2 | 345.7 | 347.0 | 348.8 | 351.3 | 352.8 | 345.3 |
| 1990 | 354.0 | 355.4 | 356.2 | 357.0 | 358.9 | 360.9 | 362.6 | - | - | - | - |
1961-1990 average concentration = 333.4 ppmv
Carbon dioxide is generally well-mixed through the global atmosphere and carbon dioxide concentrations do not vary greatly by region. The table below selects two years and four locations to illustrate this.
Annual-mean atmospheric carbon dioxide concentrations (ppmv) for 1975
and 1990 for selected sites
| 1975 | 1990 | |
| Mauna Loa | 331.0 | 354.0 |
| South Pole | 329.3 | 351.6 |
| Samoa (Eq. Pacific) | - | 352.7 |
| Barrow (Alaska) | 333.2 | 355.8 |