Over half of the carbon monoxide in the atmosphere comes from human activities including motor traffic, other combustion of fossil fuels, and slash and burn agriculture1–4. Additional anthropogenic sources include the burning of wood, savannah lands, and the oxidation of hydrocarbons including methane. Over the years these sources have increased gradually and may have already caused the concentrations of CO to double since pre-industrial times when human activities did not significantly affect the global cycles of CO and other trace gases. Increasing levels of CO can lead to an increase of tropospheric O3 (refs 5,6) and a build-up of many other trace gases in the Earth's atmosphere, which may in turn cause widespread perturbations of tropospheric chemistry, global warming, and other climatic changes7. In a recent report8 to senior US Government officials the National Academies stated the urgent need to know the global distribution and trends of CO. During the past 6–8 years we have taken systematic measurements of CO at sites ranging from within the Arctic Circle to the South Pole. The rates of increase of the globally averaged concentration are between 0.8% and 1.4% per year depending on the statistical method used for estimating the trends. These increases may have gone on for much longer because more than half of the atmospheric CO now comes from anthropogenic sources. We find that the rates of increase are largest at mid-northern and tropical latitudes, where most of the sources are located.
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Khalil, M., Rasmussen, R. Carbon monoxide in the Earth's atmosphere: indications of a global increase. Nature 332, 242–245 (1988). https://doi.org/10.1038/332242a0
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