Why Is Atmospheric Carbon Dioxide Concentration Higher in the Northern Hemisphere?

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  • TOMIZUKA Akira
    Graduate School of Fisheries Science and Environmental Studies, Nagasaki University

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  • 北半球大気の二酸化炭素濃度はなぜ高いのか？

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The atmospheric carbon dioxide (CO2) concentration is about 3 ppmv higher in the Northern Hemisphere than in the Southern Hemisphere. In this research, the reason for this difference is discussed by using a box model that facilitates the understanding of the carbon cycle. Simulation shows that the observed concentrations at Mauna Loa and the South Pole are reproduced with an exchange coefficient between hemispheres of 0.93 yr－1. This value is in close agreement with estimates from meteorological data and other models. Current atmospheric concentrations in each hemisphere are strongly dependent on the scarcity of industrial CO2 emissions in the Southern Hemisphere (only 5% of the total amount globally). A certain amount of time is needed for CO2 generated in the Northern Hemisphere to reach the South Pole, and the hemispherical difference in atmospheric concentration would be smaller if the ratio of CO2 emissions in the Southern Hemisphere were larger. On the other hand, variations in past CO2 emissions in both hemispheres resulting from changes in land use and absorption into the surface ocean and the biosphere have not been sufficiently large to affect the hemispherical difference. Specifically, the uneven hemispherical distribution of the two CO2 sinks, namely, the surface ocean and the biosphere compensate for this small effect.

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  • ENVIRONMENTAL SCIENCE

    ENVIRONMENTAL SCIENCE 26 (4), 374-387, 2013

    SOCIETY OF ENVIRONMENTAL SCIENCE, JAPAN

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