Terrestrial carbon sink in the Northern Hemisphere estimated from the atmospheric CO2 difference between Manna Loa and the South Pole since 1959

The difference between Mauna Loa and South Pole atmospheric CO2 concentrations from 1959 to the present scales linearly with CO2 emissions from fossil fuel burning and cement production (together called fossil CO2). An extrapolation to zero fossil CO2 emission has been used to suggest that the atmospheric CO2 concentration at Mauna Loa was 0.8 ppm less than that at the South Pole before the industrial revolution, associated with a northward atmospheric transport of about 1 Gt C yr(-1) (Keeling er al., 1989a). Mass conservation requires an equal southward transport in the ocean. However, our ocean general circulation and biogeochemistry model predicts a much smaller pre-industrial carbon transport. Here, we present a new analysis of the Mauna Loa and South Pole CO2 data, using a general circulation model and a 2-box model of the atmosphere. It is suggested that the present CO2 difference between Mauna Loa and the South Pole is caused by, in addition to fossil CO2 sources and sinks, a pre-industrial interhemispheric flux of 0.5-0.7 Gt C yr(-1), and a terrestrial sink of 0.8-1.2 Gt C yr(-1) in the mid-latitude Northern Hemisphere, balanced by a tropical deforestation source that has been operating continuously in the period from 1959 to the present.