CO 2 perturbation and associated global warming potentials following emissions from biofuel based on wood

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1 CO 2 perturbation and associated global warming potentials following emissions from biofuel based on wood Are biofuels carbon or climate neutral? Terje Berntsen a,b and Glen P. Peters a a Center for International Climate and Environmental Research Oslo (CICERO), Norway b Department of Geoscience, University of Oslo, Norway

2 My usual work IEA Bioenergy, Brussels, 9 March

3 Overview Motivation Climate metrics Results Carbon only (Terje) Carbon, non-co 2 forcing, albedo (Glen) Discussion IEA Bioenergy, Brussels, 9 March

4 Motivation Are biofuels carbon/climate neutral? Carbon flux (flux out equals flux in)? Yes (depending on the time-horizon/assumptions) Carbon concentration (adjust for residence time)?, not obvious Forcing neutral (recall GWP in Kyoto)?, not obvious Climate neutral (recall 2 target)?, not obvious What if we include non-co 2 forcing and albedo? IEA Bioenergy, Brussels, 9 March

5 CLIMATE METRICS IEA Bioenergy, Brussels, 9 March

6 Climate Metrics (1) More then carbon affects climate How do we compare apples with oranges? IEA Bioenergy, Brussels, 9 March

7 Climate Metrics (2) A metric helps compare apples and oranges General form of a climate metric IEA Bioenergy, Brussels, 9 March

8 Climate Metrics (3) Global Warming Potential Time horizon, 100 years (usually) a is the RF per mass increase (radiative efficiency) [ ] is the atmospheric concentration (not flux) Normalized relative to a reference gas, CO 2 E.g., CH 4 is equivalent to 21 times CO 2 in mass Can also modify the GWP for climate efficacy IEA Bioenergy, Brussels, 9 March

9 Climate Metrics (4) GWP is not perfect Many critiques and problems E.g., short-lived versus long-lived components Global Temperature Potential Converts to temperature Requires more assumptions IEA Bioenergy, Brussels, 9 March

10 Climate Metrics (summary) Carbon/climate neutrality must be relative to a metric The Kyoto Protocol sets a precedent to use GWP Others: carbon emissions, forcing, temperature, etc Time enters the metric in many ways: In the evaluation period of the metric In the life-time of the functional unit Growth cycle of the biomass Spatial boundary What area is considered? Carbon neutral in what administrative territory? IEA Bioenergy, Brussels, 9 March

11 GWP FOR BIOMASS IEA Bioenergy, Brussels, 9 March

12 Time-scales in forestry products For a given area of forest We assume all carbon oxidised in the first year Re-growth takes time Carbon emitted in year 1 will cause a forcing until sequestered Alternative views Carbon sequestered, then emitted Area is large, emission in first year is sequestered in a neighbouring area IEA Bioenergy, Brussels, 9 March

13 Tree growth Growth (kgco 2 /yr) Time (years) We take simplistic (illustrative) assumptions Proof of principle first Sequestration follows: A Guassian distribution We assume flux neutrality (flux out = flux in) More realistic functions (later) We use a standard Impulse Response Function (IRF) for the carbon cycle: Initial pulse of oxidized carbon Regrowth considered as a negative emission IEA Bioenergy, Brussels, 9 March

14 Idealized growth functions Maximum growth after 25 years Fraction of carbon remaining (unitless) CO 2 from initial pulse CO 2 from re-growth (this is negative CO 2 removed from atmosphere) Net CO 2 Growth (kgco 2 /yr) Pulse Growth Net Time Time (years) IEA Bioenergy, Brussels, 9 March

15 Why negative if flux-neutral? Carbon residence has different time-scales ~1.5 years into ocean surface Slower residence time to get to deep ocean Outgassing compensates for initial fast flux into ocean 1. Initial release into top layer of ocean, e-folding 1.5 years 2. Slower movement into lower layers of ocean 3. With slow regrowth, the initial fast uptake into the ocean must be compensated by out-gassing. Fast re-growth reduces the effect IEA Bioenergy, Brussels, 9 March

16 Idealized growth functions Fraction of carbon remaining (unitless) Fast ocean uptake (surface) Maximum growth after 25 years 2. Slower movement to deep ocean Outgassing of CO 2 Pulse Growth Net Time (years) IEA Bioenergy, Brussels, 9 March

17 Global Warming Potentials GWP100 (fossil) = 1 GWP100 = 0.44, half neutral 0.21 GWP approaches zero: for faster re-growth as time-horizon increases 0.09 GWP100 ( biofuel ) = 0 IEA Bioenergy, Brussels, 9 March

18 Temperature Response 7 x Maximum growth after 25 years Temperature from initial pulse Pulse Growth Net 5 Temperature (K/kgCO 2 ) (negative) Cooling effect of re-growth Net temperature response Growth (kgco 2 /yr) Time Time (years) IEA Bioenergy, Brussels, 9 March

19 Global Temperature Potentials GTP100 (fossil) = 1 GTP results: can be negative highly dependent on time-horizon GTP = (slow) GTP = (medium) GTP = 0 (fast) GTP100 ( biofuel ) = 0 IEA Bioenergy, Brussels, 9 March

20 But, growth cycles more realistic 1 x Assume infinite area, regrowth captures 100% of emissions Temperature (K/kgCO 2 /yr) GTP for a pulse can be negative, but... continuous growth cycles gives positive temperature for biofuels Time (years) IEA Bioenergy, Brussels, 9 March

21 IMPACT OF ALBEDO IEA Bioenergy, Brussels, 9 March

22 IEA Bioenergy, Brussels, 9 March

23 1. Initial pulse from fire, followed by decomposition and then regrowth 2. Assumes that all carbon is taken up after 80 years 3. CO 2 in atmosphere follows a ocean IRF with land IRF due to re-growth 4. Time-development of CO 2 in atmosphere. Negative after 60 years. IEA Bioenergy, Brussels, 9 March

24 Forcing due to CO 2 dominates other components Albedo causes a large cooling Average cumulative forcing, net cooling IEA Bioenergy, Brussels, 9 March

25 Cumulative Forcing (Wm -2 ) Cumulative forcing remembers albedo Year since fire CO 2 CH 4 Temperature GTP O 3 +BC+Aerosols Albedo Year since fire Net Temperature forgets albedo when forcing removed IEA Bioenergy, Brussels, 9 March

26 Global Warming Potential Global Temperature Potential Year since fire CO 2 CH 4 O 3 +BC+Aerosols Albedo Net The fire is good for climate only due to albedo Depending on fire frequency Depending on albedo change (high in boreal regions) Need region specific case studies Year since fire IEA Bioenergy, Brussels, 9 March

27 DISCUSSION IEA Bioenergy, Brussels, 9 March

28 Are biofuels carbon neutral? GWP/GTP of biofuels less than one, but greater than zero (assumption dependent) Not including LCA or LUC Biofuels are not carbon or climate neutral Approach neutral as time goes to infinity...or for fast growing cycles...or for albedo? Non-CO 2 issues relevant Albedo has a dominant impact on forcing and temperature response More then CO 2 emitted in combustion of biofuels IEA Bioenergy, Brussels, 9 March

29 Metrics for comparison Many value-laden assumptions in metrics Many additional time-dimensions with biofuels GWP remembers short-lived albedo effects GTP more realistic, but requires assumptions Global versus local response important for forests Studies should consider more than carbon LCA has locked in to a GWP100 concept CO 2, CH 4, N 2 O IEA Bioenergy, Brussels, 9 March

30 Future work Collection of (realistic) studies What are the ideal crops for different regions? What generalizations can be made? Develop albedo analysis Radiative transfer modeling important (what detail is good enough?) Albedo as a function of growth, particularly in snow What energy-balance and local effects should be included? IEA Bioenergy, Brussels, 9 March

31 QUESTIONS? IEA Bioenergy, Brussels, 9 March