A Pre-NACP Assessment of the North American Terrestrial Carbon Sink

1. A Pre-NACP Assessment of the North American Terrestrial Carbon Sink 2007 AGU Fall Meeting 13 December 2007 San Francisco, CA Anthony King Oak Ridge National Laboratory And the SOCCR SAP 2.2 Scientific Coordination Team Anthony King (ORNL) Lisa Dilling (U. Colorado/NCAR) David Fairman (CBI) R.A. “Skee” Houghton (WHRC) Gregg Marland (ORNL) Adam Rose (USC) Tom Wilbanks (ORNL) Greg Zimmerman (ORNL)

2. The U.S. Climate Change Science Program (CCSP) Strategic Plan of July 2003 calls for the creation of a series of more than 20 synthesis and assessment reports “These products will support both policymaking and adaptive management.”

3. Under CCSP Goal 2: Improve quantification of the forces bringing about changes in the Earth's climate and related systems. Topics for Priority CCSP Synthesis Products included --- North American carbon budget and implications for the global carbon cycle. U.S. Carbon Cycle Interagency Working Group had already started an initiative to produce a potentially periodic State of the Carbon Cycle Report (SOCCR)

4. The First State of the Carbon Cycle Report. SOCCR was Initiated in 2004… Released as U.S. CCSP Synthesis and Assessment Product 2.2 The First State of the Carbon Cycle Report (SOCCR): North American Carbon Budget and Implications for the Global Carbon Cycle November 13, 2007 www.climatescience.gov/Library/sap/sap2-2/final-report/default.htm cdiac.ornl.gov/SOCCR/

5. A community document with over 90 authors from Canada, USA, Mexico, and significant involvement of stakeholders Part I: The Carbon Cycle in North America (Chs. 1-5) Gives overview of the North American carbon cycle and its global context, summarizes options and measures and how to improve the relevance of carbon cycle science Part II: Energy, Industry and Waste Management (Chs. 6-9) Details budgets for emissions from various sectoral activities, including energy, transportation, industry, waste management and buildings Part III: Land and Water Systems (Chs. 10-15) Details budgets for agricultural and forest lands, permafrost, wetlands, urban areas, and coastal regions.

6. A pre-NACP North American Carbon Budget (ca. 2003) A net terrestrial sink of 500  250 Mt C yr-1 is equivalent to about 30% of North American fossil fuel emissions in 2003.

7. To summarize: The sources • North America is currently a net source of CO2 to the atmosphere. • The combustion of fossil-fuels in North America released nearly two billion metric tons of carbon to the atmosphere in 2003. • Fossil-fuel emissions are dominated by emissions from the United States (85% in 2003, Canada 9% and Mexico 6%). • Combustion of fossil fuel to produce energy commodities (primarily electricity) is the largest contributor (42% in 2003), transportation the second (31%).

8. A pre-NACP North American Carbon Budget (ca. 2003) A net terrestrial sink of 500  250 Mt C yr-1 is equivalent to about 30% of North American fossil fuel emissions in 2003.

9. Summarizing: The sinks • A terrestrial sink of 500 (50%) Mt C/year removed the equivalent of nearly 30% of North American fossil fuel emissions in 2003. • The terrestrial sink is primarily associated with regrowing forests in the United States ( 50% of the sink). • The second largest sink, woody encroachment, is also the least well known.

10. How does this sink compare with other estimates? “Bottom-up” estimates

11. How does this sink compare with other estimates? “top-down” estimates

12. Top-down estimates Gurney et al. 2004 Stephens et al. 2007 N mid-latitudes -2.4 + 1.1 -1.5 + 0.6* Tropics 1.8 + 1.7 0.1 + 0.8 North America ~20% ~33% (10-30%) (15-50%) * -1.2 with correction for rivers

13. A pre-NACP North American Carbon Budget (ca. 2003) A net terrestrial sink of 500  250 Mt C yr-1 is equivalent to about 30% of North American fossil fuel emissions in 2003.

14. Summarizing: The future of sources and sinks • The fossil-fuel emissions source is likely to increase in the future. • The future of the North American terrestrial sink is highly uncertain, with the expectation that the contribution of forest regrowth will decline as forests mature clouded by uncertainty in ecosystem response to CO2 and climate. • The current North American source:sink ratio of greater than 3:1 is likely to become larger

15. Significance of the first SOCCR (SAP 2.2) • Provides a new bottom-up synthesis of the North American carbon budget. • Sinks are collectively only 30% of fossil fuel emissions. • Forest regrowth is currently the dominant sink. • The future trajectory of this and other sinks is highly uncertain. • Effective management of North America’s contribution to global increases in atmospheric CO2 would therefore need to focus on fossil fuel emissions. • Provides a new baseline of knowledge for investigations like those of the North American Carbon Program (NACP)

16. Acknowledgements • Authors • Stakeholders • SOCCR Coordinating Team • Our Agency Sponsors • SOCCR Agency Executive Committee • The NCDC Editors and Production Team • Climate Change Science Program

17. SAP 2.2 Scientific Coordination Team • Dr. Anthony King, Oak Ridge National Laboratory- Overall Lead • Dr. Lisa Dilling, University of Colorado / National Center for Atmospheric Research- Co-Lead and Lead for Stakeholder Interaction • Mr. Gregory Zimmerman, Oak Ridge National Laboratory- Project Coordinator • Dr. David Fairman, Consensus Building Institute, Inc.- Stakeholder Interaction • Dr. Richard (Skee) Houghton, Woods Hole Research Center- Scientific Content (Land Use) • Dr. Gregg Marland, Oak Ridge National Laboratory- Scientific Content (Energy Emissions) • Dr. Adam Rose, University of Southern California- Scientific Content (Economics) • Dr. Thomas Wilbanks, Oak Ridge National Laboratory- Scientific Content (Human Dimensions)

18. Stakeholders participated from a wide variety of sectors: Government Academia Fuel producers Utilities Forestry Auto makers Agriculture Environmental advocates Carbon traders 30 people were interviewed 28 attended workshops (some more than once) Some of the companies and institutions participating: Cinergy, Pew Center on Global Climate Change, Natural Resources Defense Council, Honda Motor Company, Western Fuels, National Council for Air and Stream Improvement, Chicago Climate Exchange, The Nature Conservancy, Edison Electric Institute, Resources for the Future, Saskatchewan Soil Conservation, American Forest and Paper Association, Iowa Farm Bureau, City of Denver, U.S. Department of the Treasury, U.S. Senate staff, Monsanto, CA Air Resources Board SAP 2.2 Stakeholders

19. Thank you

20. The First State of the Carbon Cycle Report. SOCCR was Initiated in 2004… Released as U.S. CCSP Synthesis and Assessment Product 2.2 The First State of the Carbon Cycle Report (SOCCR): North American Carbon Budget and Implications for the Global Carbon Cycle November 13, 2007 www.climatescience.gov/Library/sap/sap2-2/final-report/default.htm cdiac.ornl.gov/SOCCR/

21. Top-down estimates Gurney et al. 2004 Stephens et al. 2007 N mid-latitudes -2.4 + 1.1 -1.5 + 0.6* Tropics 1.8 + 1.7 0.1 + 0.8 * -1.2 with correction for rivers

22. Treatment of uncertainty in SAP 2.2 • Sources of uncertainty vary across sectors • Variation in time and space, measurement and sampling error, uncertainty in “expansion factors” and analytical models • Uncertainty about future socio-economics and the environment, in response to perturbation, in forecasting models • To synthesize across this uncertainty and provide comparability we employed a characterization expressing relative confidence in a quantity • 95% certain that the actual value is within 10% of the estimate reported • 95% certain that the estimate is within 25% • within 50% • within 100% • uncertainty > 100%

23. Comparison with IPCC AR4 Denman et al. (2007) Northern Hemisphere and global residual terrestrial sink Given the uncertainties, the North American terrestrial sink could be as little as 6% to as much as 83% of the global terrestrial sink.