Biofuels: Comparing New
Sources with Coal, Gas, and
Kerosene
Bruce Babcock
Madhu Khanna
Puneet Dwivedi
Plausibility of CO2 Emissions from Corn
Ethanol Being Higher than Gasoline
Bruce Babcock
Iowa State University
Presented at ICABR conference, Berkeley, CA June 1, 2017.
LCA Accounting Rules (grams CO2e/MJ)
Corn Ethanol
• Ag inputs and N2O
• Distillery
• Transport & other
Subtotal
• DDGS credit
Total Emissions
Fossil Gasoline
32
31
5
68
-14
52
• Refinery
• Crude production
• Transport
Subtotal
• Tailpipe emissions
Total emissions
45% emission reduction from corn ethanol
11
6
3
20
74
94
Biogenic emissions do not get counted with LCA
• Ethanol emissions from tailpipe
• Emissions from ethanol plant
Total emissions not counted
74
33
107
Alternative Accounting Method*
• Track physical carbon flows on an annual basis (ABC).
• Any additional flow of carbon to atmosphere is an emission
• Any additional flow of carbon from the atmosphere into crops is a negative
emissions
*Plevin, RJ, MA Delucchi, and F. Creutzig. 2014. “Using attributional life cycle assessment to
estimate climate-change mitigation benefits misleads policy makers.” J. of Industrial Ecology
18:73-83.
DeCicco, et al. 2016. “Carbon balance effects of U.S. biofuel production and use.” Climatic
Change 138:667-680.
U.S. Crop Uptake of Carbon
220
215
210
205
Tg C
200
195
190
185
180
175
170
165
2005
2006
2007
2008
2009
2010
2011
2012
2013
Increase in U.S. Crop Uptake of Carbon Relative to 2005
25
20
15
Tg C
10
5
0
2005
-5
-10
-15
2006
2007
2008
2009
2010
2011
2012
2013
Increase in Biogenic Emissions from Corn Ethanol Relative to
2005
30
25
Tg C
20
15
10
5
0
2005
2006
2007
2008
2009
2010
2011
2012
2013
Change in Crop Uptake and Biogenic Emissions Relative to
2005
30
25
CO2 Emissions
CO2 Crop Uptake
20
15
Tg C
10
5
0
2005
-5
-10
-15
2006
2007
2008
2009
2010
2011
2012
2013
Cumulative Change in Crop Uptake and Biogenic Emissions
Relative to 2005
140
Only 37% of increased
biogenic emissions
offset by increased
crop uptake since
2005.
120
100
Tg C
80
60
40
20
0
2005
-20
2006
2007
2008
2009
2010
2011
2012
2013
ABC Accounting Rules (grams CO2e/MJ)
Corn Ethanol
• Total LCA Emissions
• Tailpipe emissions
• Fermentation
• Total emissions
Net crop uptake offset
Total Emissions
Fossil Gasoline
52
74
33
159
40
119
• Refinery
• Crude production
• Transport
Subtotal
• Tailpipe emissions
Total emissions
27% emission increase from corn ethanol
11
6
3
20
74
94
GHG Emissions of Corn Ethanol
Relative to Gasoline
40%
30%
20%
10%
0%
-10%
-20%
-30%
-40%
-50%
LCA
ABC
Policy-relevant question about GHGs and
ethanol that DiCiccho, et al try to answer
• What would atmospheric GHG levels (or net flows) be if
ethanol held constant at 2005 levels?
• Not the question they address in their analysis.
Price
DiCiccho’s Increased Crop
Uptake Attributed to
Ethanol
Q2005
Qobserved in 2013
Ag Output/ Crop
Uptake of CO2
Assumption 1. Behind DeCicco’s Answers
• All changes in crop uptake of CO2 relative to 2005 should be
attributed to corn ethanol.
• Strong implication about counterfactual:
Crop uptake of CO2 would have stayed constant at 2005 levels had
ethanol production not increased.
Explaining U.S. Crop Uptake of CO2 with U.S. Corn
Production
220
y = 10.294x + 74.977
R² = 0.9002
215
210
Tg C
205
200
195
190
185
180
8
9
10
11
12
Billion Bushels
13
14
15
Cumulative Change in Crop Uptake at Trend Corn Yield
(Not Actual Yield) and Biogenic Emissions Relative to 2005
140
59% of increased
biogenic emissions
offset by increased
crop uptake since
2005.
120
100
80
Tg C
60
40
20
0
2005
-20
-40
2006
2007
2008
2009
2010
2011
2012
2013
GHG Emissions of Corn Ethanol
Relative to Gasoline
40%
30%
20%
10%
0%
-10%
-20%
-30%
-40%
-50%
LCA
ABC
ABC-Trend
GHG Emissions of Corn Ethanol
Relative to Gasoline
40%
30%
20%
10%
0%
-10%
-20%
-30%
-40%
-50%
LCA
ABC
ABC Trend+2
bu
Some of the factors that caused ag output to
change from 2005 to 2013
• Ethanol production
• Weather
• Demand for domestic food (income, changes in demand composition)
• Export demand
• Government policy (eg CRP)
• Input prices
• Technological change
Conclusion 1:
• No basis for DiCiccho et al’s attribution of annual changes in crop
uptake of CO2 to ethanol.
Policy-relevant questions about GHGs and
ethanol
• What would atmospheric GHG levels (or net flows) be
without ethanol?
• What would they be without the Renewable Fuel Standard?
Alternative Counterfactual
• What would have crop uptake of CO2 been had growth in ethanol/RFS
not occurred?
• Need to construct a world without ethanol/RFS to answer this
question.
Ex post Supply2013
Price
Demand shift from
ethanol
Consumption
increase due to lower
price
2013 demand
2013 demand without ethanol
Q* Qobserved
Ag Output/ Crop
Uptake of CO2
Price
No ethanol Ex post Supply2013
Ex post Supply2013
Supply shift due to ethanol
2013 demand
2013 demand without ethanol
Q*
Qobserved
Ag Output/ Crop
Uptake of CO2
Price
No ethanol Ex post Supply2013
Ex post Supply2013
Realized change in ag output due
to ethanol.
2013 demand
Q**
Qobserved
2013 demand without ethanol
Ag Output/ Crop
Uptake of CO2
Observations
• Nothing inherently wrong with the ABC approach
• Problem is with the only published implementation
• Modeling and computational burden quite large to estimate change in ag
output and resulting change in carbon flows that should be attributed to
ethanol
•
•
•
•
Change in land use
Change in farming intensity
Change in all components of demand
Change in movement along supply and demand curves
• Also requires a dynamic model because of path dependence and future
implications on carbon flows of actions taken today
Does ethanol emit more CO2 than gasoline?
• Following the ABC approach requires bigger and better models and
more insight
• Concept that only “additional” carbon uptake should count is false
• Movement along non-biofuel demand curves creates offsets that are
just as real as increased crop uptake.