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Carbon sinks and biofuels: Optimal greenhouse mitigation strategies with inclusion of feedback effects of the global carbon cycle. Miko U.F. Kirschbaum CSIRO Forestry and Forest Products & CRC for Greenhouse Accounting Canberra, Australia [email protected] Pre-industrially 280 ppm Atmosphere 280 ppm Oceans Pre-industrially Currently 280 ppm 370 ppm 280 ppm 280 ppm Various fractions of CO2 in the atmosphere enter into pools with different turn-over times (shallow ocean, deep ocean, etc.). About 18% remain permanently in the atmosphere. Stop emissions Atmospheric CO2 (ppmv) 400 375 350 325 300 1800 1900 2000 2100 2200 Based on “Bern” model as given in IPCC (2000). 2020 2040 2060 2080 2100 0.0 -0.5 -1.0 0.5 0.0 Temperature difference (10-12 K) -0.5 -1.0 0 -1 -2 2000 2020 2040 2060 2080 2100 Difference in atmospheric carbon content (tC) Extra sink (tC) 2000 2020 2040 2060 2080 2100 0.0 -0.5 -1.0 0.5 0.0 Temperature difference (10-12 K) -0.5 -1.0 0 -1 -2 2000 2020 2040 2060 2080 2100 Difference in atmospheric carbon content (tC) Extra sink (tC) 2000 Which aspect of climate change impacts us most? Instantaneous climatic conditions? • Heat damage • Severe weather • Tropical diseases (e.g. malaria) • Food production Rate of climate change? • Ecological mal-adaptation • Socio-economic institutions Cumulative climate change? • Sea level rise T change (K) 2.5 2000 2020 2040 2060 2080 2100 SRES A2 2.0 1.5 T 1.0 0.5 10 8 6 4 2 0 Cumulative T (K yr) 150 100 50 0 2000 2020 2040 2060 2080 2100 Rate of T change [(10-3 K yr-1] 12 0.0 Time ‘bought’ by sinks 2000 2020 2040 80 Permanent 60 2060 2080 2100 Days per GtC 40 T 20 0 Temporary (20 yrs) 10 0 -10 2000 2020 2040 2060 2080 Year of sink activity 2100 Time ‘bought’ by planted forests 2000 10 2020 2040 Days per Mha planted 8 4 0 0.6 2080 2100 2080 2100 6 2 2060 T 0.4 0.2 0.0 -0.2 2000 2020 2040 2060 Planting year Biofuels Days per Mha Instantaneous impacts only Substitution 100% efficiency 5 4 3 2 1 50% 0% 0 2000 2020 2040 2060 2080 Initial planting year 2100 20-yr rotations; replanted after each harvest Days per Mha Biofuels and permanent sinks 5 4 100% Perm 3 2 1 50% 0% 0 2000 2020 2040 2060 2080 Initial planting year 2100 0 20 Carbon benefit (tC ha-1) 100 40 60 80 100 50% substitution efficiency fossil fuel offset 75 stored C 50 25 0 150 perpetual sink 100 total biofuel benefit 50 0 0 20 40 60 Years of growth 80 100 2000 2020 2040 2060 2080 2100 5 100% 4 Perm. Days per Mha 3 2 1 50% 0% 0 1.5 With wood products 20-yr 10-yr 1.0 5-yr 0.5 0.0 2000 no storage 2020 2040 2060 2080 Initial planting year 2100 Wood products with different product turn-over times Relative impact mitigation “Business-as-usual” scenario 1.0 SRES A2 0.5 0.0 -0.5 -1.0 0 20 40 60 80 100 Duration of sinks from 2000 (yrs) Relative impact mitigation “Business-as-usual” scenario 1.0 SRES A2 0.5 Average 0.0 -0.5 -1.0 0 20 40 60 80 100 Duration of sinks from 2000 (yrs) Relative impact mitigation “Sustainable” scenario 1.0 SRES B1 0.5 0.0 -0.5 -1.0 0 20 40 60 80 100 Duration of sinks from 2000 (yrs) Carbon stocks (tC ha-1) Average Carbon Stock accounting 250 Total C stocks 200 ACS 150 100 A-g biomass C stocks 50 0 0 10 20 30 40 Years 50 60 70 Carbon stocks (tC ha-1) Average Carbon Stock accounting 250 Delayed 200 crediting 150 Credit 100 50 0 0 10 20 30 40 Years 50 60 70 Conclusions (1) • Permanent carbon storage in vegetation sinks can make a small, but useful contribution. • Temporary storage is much less valuable than permanent storage, or not valuable at all. Conclusions (2) • The best timing of tree planting depends on the nature of climate change impacts: Plant now if cumulative impacts are main concern; Otherwise, later planting may be better (but that also depends on growth rate). Conclusions (3) • Biofuels can make on-going contribution (similar to permanent). • Climate-mitigation policy needs to ensure permanent storage (not tonne-year accounting). References: 1. Kirschbaum, M.U.F., Schlamadinger, B., Cannell, M.G.R., Hamburg, S.P., Karjalainen, T., Kurz, W.A., Prisley, S., Schulze, E.-D., and Singh, T.P. (2001): A generalised approach of accounting for biospheric carbon stock changes under the Kyoto Protocol. Environmental Science and Policy 4: 73-85. 2. Kirschbaum, M.U.F. (2003). To sink or burn? A discussion of the potential contributions of forests to greenhouse gas balances through storing carbon or providing biofuels. Biomass and Bioenergy 24: 297-310. 3. Kirschbaum, M.U.F. (2003). Can trees buy time? An assessment of the role of vegetation sinks as part of the global carbon cycle. Climatic Change 58: 47-71. Thank you!