240 likes | 786 Vues
Biomass Carbon Neutrality in the Context of Forest-based Fuels and Products Al Lucier, NCASI ( firstname.lastname@example.org ) Reid Miner, NCASI ( email@example.com ) May 2010 Annual U.S. Production of Renewable Materials and Biomass Energy Feedstock Circa 2005 Forest Sector & Climate Mitigation
E N D
Biomass Carbon Neutrality in the Context of Forest-based Fuels and Products Al Lucier, NCASI (firstname.lastname@example.org) Reid Miner, NCASI (email@example.com) May 2010
Annual U.S. Production of Renewable Materials and Biomass Energy Feedstock Circa 2005
Forest Sector & Climate Mitigation “In the long term, a sustainable forest management strategy aimed at maintaining or increasing forest carbon stocks, while producing an annual sustained yield of timber, fiber or energy from the forest, will generate the largest sustained mitigation benefit.” IPCC 4th Assessment Report (2007)
The “neutral” biomass carbon cycle Carbon transfers from geological reserves VS Atmosphere Non-biogenic CO2 Atmosphere CO2 Biogenic CO2 Biomass Carbon Fossil Fuel Biogenic carbon is part of a relatively rapid natural cycle that impacts atmospheric CO2 only if the cycle is out of balance Fossil fuel combustion transfers geologic carbon into the atmosphere. It is a one-way process
Implications for Carbon Accounting • Fossil Fuels: CO2 emissions at point of combustion are dominant factors in “carbon footprints.” • Forest Biomass Fuels: Changes in forest carbon stocks can be dominant factors in “carbon footprints.” • This is why there are different carbon accounting methods for fossil fuels and biomass fuels.
Biomass Carbon Neutrality (BCN) • Practical Contexts: • National Greenhouse Gas Inventory & Reporting • Cap & Trade Programs • EPA Regulation of CO2
National GHG Inventory & Reporting • BCN means that a CO2 emission factor of zero is used for biomass fuels at point of combustion. • Emissions associated with the production of biomass fuels are measured where they occur. • National GHG Inventory has two main components: (1) Emissions other than biogenic CO2 • Changes in carbon stocks • Biogenic CO2 emissions are captured in (2). • To avoid double counting, a CO2 emission factor of zero is used for biomass fuels at point of combustion.
Cap & Trade Programs • BCN is used in cap & trade programs to: • encourage use of biomass fuels in place of fossil fuels. • maintain consistency with National GHG Reporting. • Some stakeholders have expressed concerns about unintended consequences of incentives in cap & trade programs to use biomass and other energy options.
EPA Regulation of CO2 • BCN is being discussed in context of EPA’s plan to regulate CO2 as a pollutant under the Clean Air Act. Key topics include: • Legal basis for distinguishing between fossil and biomass sources of CO2. • Concerns about excessive use of biomass. • Concerns that regulating CO2 from biomass would encourage switching from biomass fuels to fossil fuels.
Why Would Eliminating BCN Encourage Switching from Forest-Based Biomass Fuels to Fossil Fuels? • At point of combustion, CO2 emissions per unit of energy produced are generally higher for biomass fuels than for fossil fuels. • This is due primarily to the higher water content of biomass fuels. • CO2 emissions at point of combustion could be reduced by shifting fuel mix away from biomass. • However, overall CO2 emissions would increase in most cases.
Biomass Carbon Neutrality • Does not measure reductions in GHG emissions attributable to using bioenergy instead of fossil energy.
Quantifying GHG Benefits of Bioenergy • Construct scenarios. • Estimate cumulative emissions for each scenario.
What if a new biomass production system is gradually replacing forest that has higher carbon stocks? Net cumulative emissions for biomass system increase to reflect stock losses , but stop increasing after all plots have been converted to production forest. Biomass energy Fossil fuel energy Cumulative CO2 combustion emissions Net Cumulative CO2 combustion emissions Time Time
This increases the time required for biomass to show net benefits, but after the “break even point” the benefits of biomass continue to accrue. Biomass energy Fossil fuel energy Cumulative CO2 combustion emissions Net Cumulative CO2 combustion emissions Biomass lower from here forward Time Time
If reductions in land-based carbon are lower, the time to “break even” is reduced. Biomass energy Fossil fuel energy Cumulative CO2 combustion emissions Net Cumulative CO2 combustion emissions Biomass lower from here forward Time Time
Of course, the opposite can happen. Land can be converted to higher carbon stocks to provide biomass energy (e.g. afforestation). Biomass energy Fossil fuel energy Cumulative CO2 combustion emissions Net Cumulative CO2 combustion emissions Cumulative fossil fuel carbon emissions continue to increase indefinitely Time Time Cumulative net biomass emissions remain below zero
So, we have seen that the net cumulative emissions of biogenic carbon vary depending on whether and how the overall carbon stocks on the land are changing. In the United States, carbon stocks on wood-producing land are stable or increasing, so the national situation is best represented by this line. Convert land to much lower carbon stocks Net Cumulative biogenic CO2 emissions Convert land to somewhat lower carbon stocks Keep land in same general forest type Time This means that the forest biomass carbon placed in the atmosphere is offset by new forest growth on wood-producing land Afforestation or other increase in carbon density
Timberland Growth/Removal Ratio By Region • Growth-removal ratio is calculated based on annual growth on timberland divided by annual removal as of reported years. No specific data for growth and removal in between reported years. Source: Forest Resources of the United States, 2007 – Table 36
“Life Cycle” Emissions of Greenhouse Gases Other than Biogenic CO2 Data sources: IPCC, USDOE USLCI Database, other public life cycle databases
Summary • US Forest Sector • A world leader in biomass energy production & use. • Part of the solution to greenhouse gas mitigation. • Biomass Carbon Neutrality (BCN) • In theory, an attribute of biomass energy systems where the biogenic carbon cycle is in balance. • In practice, an accounting convention in national greenhouse gas inventories.
Summary • In the United States, • forest carbon stocks are stable or increasing; • therefore, GHG emissions per unit of energy are much lower for forest biomass fuels than for fossil fuels. • EPA is considering whether to eliminate BCN for purposes of regulating CO2 as a pollutant under the Clean Air Act. • EPA deferred decision on BCN in “tailoring rule” • Eliminating BCN in this context would encourage replacement of biomass will fossil fuels, resulting in substantial increases in GHG emissions.