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Published November 27, 2007 | Published + Supplemental Material
Journal Article Open

An atmospheric perspective on North American carbon dioxide exchange: CarbonTracker


We present an estimate of net CO2 exchange between the terrestrial biosphere and the atmosphere across North America for every week in the period 2000 through 2005. This estimate is derived from a set of 28,000 CO2 mole fraction observations in the global atmosphere that are fed into a state-of-the-art data assimilation system for CO2 called CarbonTracker. By design, the surface fluxes produced in CarbonTracker are consistent with the recent history of CO2 in the atmosphere and provide constraints on the net carbon flux independent from national inventories derived from accounting efforts. We find the North American terrestrial biosphere to have absorbed –0.65 PgC/yr (1 petagram = 10^15 g; negative signs are used for carbon sinks) averaged over the period studied, partly offsetting the estimated 1.85 PgC/yr release by fossil fuel burning and cement manufacturing. Uncertainty on this estimate is derived from a set of sensitivity experiments and places the sink within a range of –0.4 to –1.0 PgC/yr. The estimated sink is located mainly in the deciduous forests along the East Coast (32%) and the boreal coniferous forests (22%). Terrestrial uptake fell to –0.32 PgC/yr during the large-scale drought of 2002, suggesting sensitivity of the contemporary carbon sinks to climate extremes. CarbonTracker results are in excellent agreement with a wide collection of carbon inventories that form the basis of the first North American State of the Carbon Cycle Report (SOCCR), to be released in 2007. All CarbonTracker results are freely available at http://carbontracker.noaa.gov.

Additional Information

© 2007 National Academy of Sciences of the USA. Freely available online through the PNAS open access option. Communicated by A. R. Ravishankara, National Oceanic and Atmospheric Administration, Boulder, CO, September 27, 2007 (received for review May 23, 2007). We thank Taro Takahashi, Greg Marland, T. J. Blasing, Tris West, Jerry Olson, and the EDGAR consortium for contributing data sets used to complete this study. Development of the GFED2 fire emissions was supported by National Aeronautics and Space Administration Grant NNG04GK496. The column CO2 observations at Park Falls were obtained with support from National Aeronautics and Space Administration Grant NNG05GD07G. CarbonTracker is a National Oceanic and Atmospheric Administration contribution to the North American Carbon Program. Author contributions: P.P.T. designed research; C.S., A.E.A., T.J.C., D.E.J.W., G.R.v.d.W., J.T.R., and P.O.W. contributed data; A.R.J., K.M., J.B.M., L.M.P.B., G.P., A.I.H., and M.C.K. performed research; and W.P. wrote the paper. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/cgi/content/full/0708986104/DC1.

Attached Files

Published - PETpnas07.pdf

Supplemental Material - PETpnas07appendix.pdf


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