Greenhouse-Gas Consequences of US Corn-based Ethanol Policies

Transcription

1 Greenhouse-Gas Consequences of US Corn-based Ethanol Policies Michael T. Coe and Eric A. Davidson1, Daniel C. Nepstad2, Simon D. Donner3, Mercedes M. C. Bustamante4, and Chris Neill5 1The Woods Hole Research Center; 2 The Gordon and Betty Moore Foundation; 3University of British Columbia; 4Universidade de Brasília; 5MBL

2 In his 2007 State of the Union address, President Bush proposed increasing annual ethanol production to 133 billion liters by Congress specified a similar production goal for 2022 in the 2007 energy bill, but with a cap of 57 billion liters per year from corn and the remainder to be derived from cellulosic materials, starting in 2016.

3 In his 2007 State of the Union address, President Bush proposed increasing annual ethanol production to 133 billion liters by Congress specified a similar production goal for 2022 in the 2007 energy bill, but with a cap of 57 billion liters per year from corn and the remainder to be derived from cellulosic materials, starting in The objective of this study is to improve estimates of the potential net greenhouse gas consequences, both domestically and in Brazil, of meeting the goals established by the US Congress for expansion of corn-based ethanol in the USA.

4 Commodities Prices

5 US Ethanol Production 2008 (b/d)

6 US Ethanol Production Goal Increased Area Planted in Corn in USA Soy to Corn Conversion CRP to Corn Conversion Economic impacts of crop prices Environmental impacts in USA Suitability of CRP land for corn Environmental impacts in USA Food prices Soy expansion in Brazil N pollution of streams and groundwater; Soil C loss and erosion Economic impacts Environmental impacts in Brazil: Net GHG emissions from new deforestation Habitat loss Potential change in water quality and quantity Indirect effects of US agricultural and energy policies

7 The USA and Brazil currently account for about 71% of global soy exports, with Brazil recently surpassing the USA as the leading exporter of soybeans. Soy Suitability Stickler et al. Only a few countries, mainly Brazil, have appropriate soils, climate, and infrastructure needed for large absolute increases in cropped area in the next decade that could make up the lost US soybean production. forest non-forest

8 Soy planted area increased in Brazil by 500,000 ha in 2007/2008 (relative to 2006) as a result of increased commodities prices, at least in part due to decreased planted area in US New planted area in Brazil often comes from conversion of pasture, Cerrado, and forest, not from changes in rotation frequency or from other crops as it does in the US.

9 Our study focuses on consequences specific to Brazil, using recent field data from Amazon and Cerrado ecosystems. We perform a simple scale analysis; asking first, how much land is required to create corn for 57 billion liters of ethanol, and second, what are the potential greenhouse gas consequences in Brazil? Landcover data from Ramankutty and Foley 1998

10 For simplicity, we assume flat demand for non-ethanol corn products (273 x 10 9 kg corn) and a constant ethanol conversion rate (403 liters ethanol/mg corn) to 2022 to calculate the amount of annual corn production needed to meet the Congressional goal of 57 billion liters annual corn-based ethanol production: Production = 57 x 10 9 liters x 1kg corn/0.403 liter = 141 x 10 9 kg corn We then estimate the area that will have to be planted in corn annually to meet the current non-ethanol demand for corn (273 x 10 9 kg) plus this additional 141 x 10 9 kg corn needed to meet the Congressional ethanol production goal. Assuming current mean corn yield for the region (0.945 kg/m 2 ), the area needed to meet this production rate is: Area = ( ) x 10 9 kg x 1 m 2 /0.945 kg = 4.38 x m 2 = 44 x 10 6 ha This estimate of 44 million hectares planted in corn is an increase of 7 million hectares beyond the record 2007 planted area of 37 million hectares.

11 Corn yield is likely to increase, but the recent historic projection of crop yield increases of 1% per year is probably overly optimistic, because modern hybrid corn may be approaching biophysical limits for grain production.

12 Corn yield is likely to increase, but the recent historic projection of crop yield increases of 1% per year is probably overly optimistic, because modern hybrid corn may be approaching biophysical limits for grain production. The efficiency of ethanol production will also increase and non-ethanol demands might decrease. An optimistic scenario for increasing crop yield might also cover these other effects.

13 A second scenario assumes that corn yield will increase 1% annually, reaching kg/m 2 by 2022: Area = ( ) x 10 9 kg x 1 m 2 /1.097 kg = 3.77 x m 2 = 38 x 10 6 ha This optimistic scenario results in needing 1 million additional hectares planted in corn beyond the 2007 planted area.

14 Global Warming Potential Cerrado Conversion Cattle CH 4

15 Soil CH 4 Cattle CH 4 Soil N 2 0 CO 2 Equivalents (Mg CO 2 ha -1 ) Global Warming Potential Forest Conversion

16 CO 2 Equivalent GHG Emissions The CO 2 equivalents (integrated over 100 years) of life-cycle avoided fossil fuel emissions from corn-based ethanol production within the USA and from the greenhouse gas emissions resulting from unintentional deforestation in Brazil linked to recent, current, and future scenarios of US expansion of corn-based ethanol production.

17 CO 2 Equivalent GHG Emissions The CO 2 equivalents (integrated over 100 years) of life-cycle avoided fossil fuel emissions from corn-based ethanol production within the USA and from the greenhouse gas emissions resulting from unintentional deforestation in Brazil linked to recent, current, and future scenarios of US expansion of corn-based ethanol production.

18 The GHG emissions resulting from either Cerrado or Amazonian deforestation range from 130 to 650 times higher than the estimates of annual net GHG emissions diverted in the USA from ethanol production. Hence, it would take >130 years of 57 billion liters per year of US cornbased ethanol to make up for the greenhouse gases emitted from the unintended land-use consequences in Brazil.

19 Fargione et al. (2008) make calculations of a similar, but shorter, carbon debt pay-back period, assuming that the Cerrado will be converted for sugar cane ethanol. Our estimates are based on Cerrado conversion to soybeans in response to increased cornbased ethanol production in the USA. Both are occurring.

20 Mitigation strategies Expanding row crop agriculture on land that has already been cleared for cattle pastures would result in less loss of aboveground biomass carbon how much suitable degraded cattle pasture is available?

21 Mitigation strategies Expanding row crop agriculture on land that has already been cleared for cattle pastures would result in less loss of aboveground biomass carbon how much suitable degraded cattle pasture is available? Intensification of crop and cattle production within Brazil in response to rising land prices could also result in less land being deforested.

22 Mitigation strategies Expanding row crop agriculture on land that has already been cleared for cattle pastures would result in less loss of aboveground biomass carbon how much suitable degraded cattle pasture is available? Intensification of crop and cattle production within Brazil in response to rising land prices could also result in less land being deforested. However, even if only 15% of the Brazilian deforestation calculated here occurs ( ha), the carbon pay-back time of US corn-based ethanol production would be decades to a century.

23 These results demonstrate that a slight mitigation in domestic accounting of GHG emissions in the USA is likely to be overwhelmed by a large net increase of greenhouse-gas emissions due to land use change in Brazil in response to decreased soybean production in the USA.

24 These results demonstrate that a slight mitigation in domestic accounting of GHG emissions in the USA is likely to be overwhelmed by a large net increase of greenhouse-gas emissions due to land use change in Brazil in response to decreased soybean production in the USA. Other motivations for advancing corn-based ethanol production in the USA, such as reduced reliance on foreign oil and increased prosperity for farming communities, must be considered separately, but the greenhouse-gas-mitigation rationale is unsupportable.

25 Agricultural expansion in Brazil yields significant economic benefits, but these considerations should not be confused with a justification of a net positive balance for GHG emissions, which requires a significant payback period.

26 Agricultural expansion in Brazil yields significant economic benefits, but these considerations should not be confused with a justification of a net positive balance for GHG emissions, which requires a significant payback period. Biofuel production will most likely increase in the USA, Brazil, and elsewhere with or without a legitimate greenhouse-gas mitigation rationale.

27 Agricultural expansion in Brazil yields significant economic benefits, but these considerations should not be confused with a justification of a net positive balance for GHG emissions, which requires a significant payback period. Biofuel production will most likely increase in the USA, Brazil, and elsewhere with or without a legitimate greenhouse-gas mitigation rationale. A combination of improved N- fertilizer-use-efficiency and efforts to constrain deforestation are needed to reduce the impact of biofuel expansion on greenhouse-gas emissions and on other societal concerns.

28 The USA-Brazil soybean connection demonstrates the importance of increasingly interconnected agriculture and energy markets and their cascading social, environmental, and economic consequences, which clearly extend beyond national boundaries. Thank you.