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Science 22 June 2007:
Vol. 316. no. 5832, pp. 1732 - 1735
DOI: 10.1126/science.1137004
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Reports

Weak Northern and Strong Tropical Land Carbon Uptake from Vertical Profiles of Atmospheric CO2

Britton B. Stephens,1* Kevin R. Gurney,2 Pieter P. Tans,3 Colm Sweeney,3 Wouter Peters,3 Lori Bruhwiler,3 Philippe Ciais,4 Michel Ramonet,4 Philippe Bousquet,4 Takakiyo Nakazawa,5 Shuji Aoki,5 Toshinobu Machida,6 Gen Inoue,7 Nikolay Vinnichenko,8{dagger} Jon Lloyd,9 Armin Jordan,10 Martin Heimann,10 Olga Shibistova,11 Ray L. Langenfelds,12 L. Paul Steele,12 Roger J. Francey,12 A. Scott Denning13

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.

1 National Center for Atmospheric Research, Boulder, CO 80305, USA.
2 Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907, USA.
3 National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA.
4 Le Laboratoire des Sciences du Climat et l'Environnement, 91191 Gif sur Yvette, France.
5 Center for Atmospheric and Oceanic Studies, Tohoku University, Sendai 980-8578, Japan.
6 National Institute for Environmental Studies, Onogawa, Tsukuba 305-8506, Japan.
7 Graduate School of Environmental Studies, Nagoya University, Nagoya City 464-8601, Japan.
8 Central Aerological Observatory, Dolgoprudny, 141700, Russia.
9 School of Geography, University of Leeds, West Yorkshire, LS2 9JT, UK.
10 Max Planck Institute for Biogeochemistry, 07701 Jena, Germany.
11 Sukachev Institute of Forest, Krasnoyarsk, 660036, Russia.
12 Commonwealth Scientific and Industrial Research Organisation (CSIRO) Marine and Atmospheric Research, Aspendale, Victoria 3195, Australia.
13 Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523, USA.

{dagger} Deceased.

* To whom correspondence should be addressed. E-mail: stephens{at}ucar.edu

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