An atmospheric perspective on North American carbon dioxide exchange: CarbonTracker

TLDR

The study estimates weekly net CO₂ exchange between North American terrestrial biosphere and atmosphere from 2000 to 2005. The estimate is derived by assimilating 28,000 atmospheric CO₂ observations into the CarbonTracker data‑assimilation system, producing surface fluxes consistent with recent atmospheric CO₂ history and independent of national inventories. North America’s terrestrial biosphere absorbed an average of 0.65 PgC yr⁻¹ (−0.4 to −1.0 PgC yr⁻¹) between 2000–2005, mainly in East Coast deciduous and boreal coniferous forests, with uptake dropping to 0.32 PgC yr⁻¹ during the 2002 drought, and the estimate aligns with inventories used for the 2007 State of the Carbon Cycle Report. All CarbonTracker results are freely available at http://carbontracker.noaa.gov.

Abstract

We present an estimate of net CO(2) 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 CO(2) mole fraction observations in the global atmosphere that are fed into a state-of-the-art data assimilation system for CO(2) called CarbonTracker. By design, the surface fluxes produced in CarbonTracker are consistent with the recent history of CO(2) 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.