Stephens, B. B., K. R. Gurney, Pieter P. Tans
, Colm Sweeney
, W. Peters
, Lori M. P. Bruhwiler
, P. Ciais, M. Ramonet, P. Bousquet, T. Nakazawa, S. Aoki, T. Machida, G. Inoue, N. Vinnichenko, J. Lloyd, A. Jordan
, M. Heimann, O. Shibistova, R. Langenfelds, L. P. Steele, R. J. Francey and A. S. Denning, (2007), Weak northern and strong tropical land carbon uptake from vertical profiles of atmospheric CO2, Science
, 316, 5832, 1732-1735, 10.1126/science.1137004
Measurements of midday vertical atmospheric CO2 distributions reveal annual-mean vertical CO2 gradients that are inconsistent with atmospheric models that estimate a large transfer of terrestrial carbon from tropical to northern latitudes. The three models that most closely reproduce the observed annual-mean vertical CO2 gradients estimate weaker northern uptake of -1.5 petagrams of carbon per year (Pg C year-1) and weaker tropical emission of +0.1 Pg C year-1 compared with previous consensus estimates of -2.4 and +1.8 Pg C year-1, respectively. This suggests that northern terrestrial uptake of industrial CO2 emissions plays a smaller role than previously thought and that, after subtracting land-use emissions, tropical ecosystems may currently be strong sinks for CO2.