feeding a hot and hungry planet tim searchinger princeton university [email protected]
TRANSCRIPT
Ag’s Contribution to World Greenhouse Gases ~ 30%
(IPCC 2007; Bellarby 2008 , in CO2 eq.)
• Nitrous oxide – fertilizer, manure
• Methane – cows, rice, manure, biomass burning
• Energy – farm machinery, fertilizer, irrigation pumps
• 33 million acres/yr gross deforestation
Non-Ag33.5 Gt
69%
Ag Land Expansion
8.5Gt17%
CO2 from Energy
Use1 Gt2% N2O and
NH46 Gt12%
2004
49 Gt Total
Land Use Change
Biofuels send price signal:
Undernourished People and Recent Changes
Source: FAO. 2009. The State of Food Insecurity In the World, 2008
- 16% of world malnourished- 1/3 of children in developing world stunted- 30 million babies born impaired due to lack of natal nutrition - 5 million children die annually from causes related to lack of nutrition
The Hunger ChallengeThe Hunger Challenge
Source: Keyzer 2006
Food for a Week, Darfur Refugees, Chad© 2007 PETER MENZEL PHOTOGRAPHY
Food for a Week, Germany© 2005 PETER MENZEL PHOTOGRAPHY
Tilman, Forecasting Global Agricultural Driven Environmental Consequences
IrelandUK
DenmarkSweden
Netherlands
Belgium
Germany
France
Rwanda
Zimbabwe
Namibia
Zambia
Egypt
R2 = 0.8788
0
0.5
1
1.5
2
2.5
3
0 2000 4000 6000 8000 10000
Yield (kg ha-1)
Cro
p W
ater
Pro
du
ctiv
ity
(kg
m-3
)
Asia
Europe
North America
South America
Africa
Oceania
Ireland
UK
DenmarkSweden
Eritrea
Chad
Sudan
Mali
R2 = 0.7859
0
0.5
1
1.5
2
2.5
3
0 2000 4000 6000 8000 10000 12000 14000
Yield (kg ha -1)
Cro
p W
ater
Pro
du
ctiv
ity
(kg
m-3
)
Asia
Europe
North America
South America
Africa
Oceania
Potential yield and yield gap at a global scale
GEPIC Outputs: global map of wheat yield
crop water productivity of wheat
Areas of Water Stress
Can we limit LUC for food alone
Optimism
• Big yield gaps• Much food waste• Biotechnology• Livestock intensification
potential
Pessismism
• Declining trend lines• Irrigation limits• Improved knowledge for
tropical forest agriculture• Population? • Climate change (high
temperature; declining snowpack)
IPCC SRES ScenariosPredicted Emissions from Land Use Change
Year B-1 B-2
2020 2.2 0
2050 -0.4 -0.2
Other Uses of Land
• More cropland and pasture for food –200-500 million hectares by 2050
• Terrestrial carbon sink – 9.5 GT CO2/yr
• Avoided deforestation potential – 9 Gt/year
• Afforestation mitigation potential – 4 Gt/year
• Restore peatlands – 1.3 gigatons/year
All from IPCC 2007 Mitigation Report, chapters 8 & 9
Agriculture Mitigation Potential at $100/t
Some Technical Options
Somewhat Known
• Crop & livestock yield gains
• Chickens, tilapia over beef
• Manure biogas
• Improved N use efficiency
• Livestock feeding
• Pasture improvement
• Some rice water management
Innovations Required
• Perennial feed crops & other new cropping systems
• Cover crops?
• Cow stomach bug changes
• More nitrogen crops
• Upland or alternative rice
• New nitrification inhibitors
• Biochar
Conventional approach But . . .
Land grows plants (carbon) anyway
* forest
* food
Only ADDITIONAL plant growth helps
Biofuels & Greenhouse Gases
Direct Effects of Diverting Crops to Biofuels – No Change in Emissions
Corn uptake
Car, gasoline
Corn uptake
Car, ethanol
Indirect Scenario 1 – Ethanol Leads to Less Crop Consumption for Food, which Reduces CO2
Crop uptake
Car, gasoline
Livestock & human
respiration
Crop uptake
Car, ethanol
Reduced livestock & human
respiration
Indirect Scenario 2 – Ethanol Leads to Yield Growth on Existing Farmland to Replace Diverted Crops, which Absorb More Atmospheric Carbon and Reduces CO2
Car, gasoline
Crop uptake
Increased yields, which absorb more carbon on the same land but may
involve increased emissions from inputs, such as nitrous oxide
Car, ethanol
N2O Formation Rate
Greenhouse gases (CO2 eq.)/km
2% 401
3% 603
4% 803
5% 1003
6% 1204
GHGs from Nitrous Oxide For Yield Gains
Through Fertilizer (assuming 7 extra additional lbs of fertilizer/bushel of corn)
Compare 316 g/km from land use
Implied Yield Growth by 2020Scenario 10.2% Transport
Fuel(Etech 4)
Crop Biofuels, adjusted for by products
Non Biofuel food demand
Biofuel and Non Biofuel
1996-2006 Trend
Cereals (corn,wheat 0.8% 1.8% 2.6% 1.3%Oilseeds (soy, rape) 0.9% 2.2% 3.2% 1.5%Sugar (cane) 5.0% 0.6% 5.5% 0.8%
Palm 3.0% 3.9% 6.9% 1.9%
Viewed as Opportunity CostCarbon Benefit• 3 t/ha/yr – corn ethanol – GREET (incorporating by-product
credit)• 8.6 t/ha/yr – cellulosic ethanol – GREET (swtichgrass at 18
t/ha/yr, 359 l/t)Carbon Cost• Fallow land - forest regeneration temperate, 7.5-12 t/ha/yr• Forest regeneration tropical – 20+ t/ha/yr• Existing forest (lose 600-1000 tons) 15-35 t/ha/yr (over 30
years)• Existing grassland/savannah (lose 75-300 tons), 2.5-10 t/ha/yr
(over 30 years) plus lost forage
Bioenergy
How? • Large % of potential arable land – IPCC 2007 chapter
8 (based on Smith 2007) 1.3billion hectares and/or
• All forest growth in excess of harvest (Smeets 2008)and/or
• All “abandoned” cropland (Hoodwijk (2004) and/or
• Hundreds of millions of hectares of “grazing” or “other” land – savannah (Fischer 2001; Smith 2007)
Recounts existing forest, forest re-growth, net terrestrial carbon sink, land counted for grazing
Exemption for Bioenergy
Under a Cap & Trade System
• IPCC 2000 Land Use Report (p. 355): Because “fossil fuel substitution is already ‘rewarded’” by excluding emissions from the combustion of bioenergy, “to avoid underreporting . . . any changes in biomass stocks on lands . . . resulting from the production of biofuels would need to be included in the accounts.”
The Big Issue
Natural Forest
Natural Forest (Melillo, Gurgel, et al. 2008)
Natural Forest (“Deforestation” Scenario)
Natural Forest
Wise et al., Science 324:1183 (2009)
National Academy of Sciences (May 2009)
• "If food crops or lands used for food production are diverted to produce biofuels rather than food, additional land will probably be cleared elsewhere in the world and drawn into food production. The greenhouse gas emissions caused by such clearing of land, especially forests, will decrease or even negate the greenhouse-gas benefits of the resulting biofuels." p. 79
• "Producers need to grow biofuel feedstocks on degraded agricultural land to avoid direct and indirect competition with the food supply and also need to minimize land-use practices that result in substantial net greenhouse-gas emissions." p. 79
Other 2008/09 Studies – Similar Conclusions
• UK Renewable Fuels Agency (Gallagher Review)
• EU Joint Research Center
• World Bank• FAO• Netherlands
Environmental Assessment Agency
• OECD• European Economic
and Social Committee• Scientific Committee
on Problems of the Environment
• British Royal Society