Reconciling estimates of the contemporary North American carbon balance among an inventory-based approach, terrestrial biosphere models, and atmospheric inversions

Daniel Hayes, ORNL, hayesdj@ornl.gov (Presenter)
David Turner, Oregon State University, david.turner@oregonstate.edu
Graham Stinson, Canadian Forest Service, gstinson@pfc.cfs.nrcan.gc.ca
A. David McGuire, USGS, admcguire@alaska.edu
Yaxing Wei, ORNL, weiy@ornl.gov
Tristram O. West, Joint Global Change Research Institute, tristram.west@pnl.gov
Linda Heath, USDA Forest Service, NRS, lheath@fs.fed.us
Bernardus de Jong, ECOSUR, bjong@ecosur.mx
McConkey Brian, Environment Canada, brian.mcconkey@agr.gc.ca
Richard Birdsey, USDA Forest Service, rbirdsey@fs.fed.us
Werner Kurz, Canadian Forest Service, Natural Resources Canada, wkurz@nrcan.gc.ca
Andy Jacobson, NOAA, andy.jacobson@noaa.gov
Deborah Nicole Huntzinger, Northern Arizona University, deborah.huntzinger@nau.edu
Yude Pan, USDA Forest Service, ypan@fs.fed.us
Wilfred M. Post, Oak Ridge National Laboratory, wmp@ornl.gov
Robert B. Cook, Environmental Sciences Division, ORNL, cookrb@ornl.gov

Although the exact contribution is uncertain, North American (NA) ecosystems are thought to have a significant influence on the global carbon budget by acting as a large sink of atmospheric CO2 in recent decades. Assessments of the continental carbon balance have been based on various scaling approaches, including top-down atmospheric inverse models (AIMs) and bottom-up terrestrial biosphere models (TBMs), which vary widely in their estimates of the magnitude, timing and spatial pattern of sources and sinks of atmospheric CO2. A suite of results on NA ecosystem carbon flux from extant model simulations (based on both AIMs and TBMs) have been organized by the North American Carbon Program (NACP). Here, we assemble and analyze available inventory-based data on NA ecosystem carbon cycle components as an additional perspective alongside the NACP models. We develop an inventory-based approach for estimating net ecosystem exchange (NEE) over NA that notably retains information on the spatial distribution of the vertical fluxes as well as accounting for lateral transfers.

The total inventory-based NEE estimate of a -327 ± 252 TgC yr-1 sink for NA was driven primarily by CO2 uptake in the Forest Lands (-248 TgC yr-1) and in the Crop Lands (-297 TgC yr-1) sectors. These sinks are counteracted by the CO2 source estimated for the Other Lands sector (+218 TgC yr-1), where much of the forest and crop products are returned to the atmosphere through consumption and decay. The ecosystems of Mexico are estimated to be a small net source (+18 TgC yr-1) due to land use change. We compare these inventory-based estimates with results from the TBMs and AIMs, where the mean continental-scale NEE estimate for each ensemble is -511 TgC yr-1 and -931 TgC yr-1, respectively. Additional fluxes not measured by the inventories, though highly uncertain, could add an additional -239 TgC yr-1 to the inventory-based NA sink estimate, thus suggesting some convergence with the modeling approaches. Depending on the approach, the estimates of the NA sink presented here represent between 18% and 52% of continental fossil fuel emissions over this same time period.

Presentation Type:  Poster

Session:  Global Change Impact & Vulnerability   (Tue 11:30 AM)

Associated Project(s): 

• Hayes, Daniel: Diagnosis and attribution of the contemporary North American terrestrial CO2 sink: the role of disturbance and land use change ...details

Poster Location ID: 205