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 concentrati ons from 1959 to the present scales linearly with CO2 emissions from fossil fuel burning and cement production (together called fossil CO2). An extrap olation to zero fossil CO2 emission has been used to suggest that the atmos pheric CO2 concentration at Mauna Loa was 0.8 ppm less than that at the Sou th Pole before the industrial revolution, associated with a northward atmos pheric transport of about 1 Gt C yr(-1) (Keeling er al., 1989a). Mass conse rvation requires an equal southward transport in the ocean. However, our oc ean general circulation and biogeochemistry model predicts a much smaller p re-industrial carbon transport. Here, we present a new analysis of the Maun a Loa and South Pole CO2 data, using a general circulation model and a 2-bo x 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 CO 2 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 b een operating continuously in the period from 1959 to the present.