The global distribution of atmospheric carbon dioxide: 2. A review of provisional background observations, 1978–1980

An attempt is made to bring together provisional data collected throughout the world to construct a global picture of the background atmospheric carbon dioxide concentration distribution. The uncertainties, calibration and sampling difficulties, and measurement needs are discussed, and it is concluded that in general the accuracy of the provisional data at each sampling location is ∼±1 ppmv. Ongoing studies at the main laboratories are likely to significantly improve this accuracy in the near future. The most recent data available (for 1980) indicate annual average northern hemisphere high latitude CO 2 concentrations 4 to 5 ppmv above those at high latitudes of the southern hemisphere (∼336 ppmv). The greatest uncertainty in the zonal average concentration exists in the latitude band 10–30°N where surface observations are 2–3 ppmv higher than those measured by continuous analysis at the Mauna Loa Observatory. There is generally good agreement between a model‐generated and the observed annual mean global distributions. The seasonality of concentration is small in the southern hemisphere (∼1–2 ppmv peak to peak) rising to ∼6 ppmv at 20°N and ∼15 ppmv at high latitudes of the northern hemisphere. The total global atmospheric CO 2 content, averaged through 1980, is estimated to have been 7.15×10 14 kg of carbon with a probable uncertainty of 0.5 to 1.0%.