Biofuels: A sober look at the potential Chris Field Carnegie Institution: Department of Global Ecology Stanford University, Department of Biology Bioenergy basics Bioenergy options Bioenergy potential

Why biofuels? Climate protection –Offset fossil fuels –Account for fossil fuels used to produce –Account for site carbon balance –Account for other greenhouse gases Energy security –Local potential –Diversify sources

How can biofuels be lower carbon? Photosynthesis –Light + CO 2 plant + O 2 Plant combustion –Plant + O 2 energy + CO 2 Net –Light + CO 2 energy + CO 2

How Biomass is Used for Energy MatureSemi-mature (Capital intensive ineficient) In development

Carbon cycle basics Fossil fuel + oxygen  carbon dioxide –Coal: C + O 2  CO 2 –Oil: C 8 H O 2  8CO 2 + 8H 2 O –Natural Gas: CH 4 + 3O 2  CO 2 + 2H 2 O How much CO 2 ? –Burning 1 lb of coal produces 3.6 lb of CO 2 –Burning 1 gal of gas produces 18 lb of CO 2 –The average person produces 30 lb CO 2 /day –The average American produces 170 lb CO 2 /day

Setting the scale Food for 1 person for one year –~ 250 kg corn = ethanol for one fill-up –~ 80 l (20 gal) At 25 mpg and 10,000 miles/y –The corn required to fuel one car on corn ethanol –Would feed 25 people

0.5 MJ speeding car 1 kJ1 MJ1 GJ1 TJ1 PJ1 EJ1 YJ1 ZJ1 J GJ =ton TNT 6 GJ = barrel crude oil J biggest nuclear bomb 1 kg matter J car/yr 1 MJ 240 kcal 100 J action 4 ·10 22 J World fossil Fuel reserves 450 EJ world energy consump/yr J 1 gram E = Mc 2 Powers of ten Energy 12 ·10 15 J supertanker QUADBTU 10 MJ 2400 kcal human/day 1 ZJ KT impact 5 ZJ Solar energy On Earth in 1 year

Today, the world consumes 20X as much energy as in 1900!

Future energy needs: Many times current

Global annual plant growth ~57 x 10 9 ton C on land ~57 x 10 9 ton C in the oceans = 2500 EJ or 5 x global primary energy

Land Type Area (Mha) Mean NPP (ton C/ha/y) Total NPP (Pg C/y) Total Energy* (EJ/y) GlobalCrop1, Pasture3, USCrop Pasture Global Primary Energy = 450 EJ/y * In ½ biomass (to allow for roots), assume 45% C Energy in ag and pastures?

Will yields increase dramatically? Historical trends – a century of success –1-2%/y for major crops Will this continue? –Can it accelerate?

Ag yields – a century of success increases of 1-2% y -1 Lobell and Field ERL 2007

Limiting factors for global NPP Baldocchi et al SCOPE 62

Potential yield Ag in relation to natural NPP –Ag/NPP -- Globally about 65% Global average crop yields unlikely to exceed natural NPP for at least the next several decades 15

Burn or Ferment? If you want energy –Burn If you want oil independence –Liquid biofuels –Battery technology

Net energy balance ratio (biomass energy out/fossil energy in) Corn ethanol ~1.2 Sugarcane ethanol ~ 8 Soy biodiesel ~ 2 Palm biodiesel ~ 9 Cellulosic ~5(?)

Hill et al PNAS 2006

Is sugarcane the answer? High yields in warm, wet climates Limited need for fossil energy –Burn bagasse for processing energy

Fargione et al. Science 2008

Is cellulosic the answer? Yield of 26.5 tons/acre in limited area test plots Courtesy of Steve Long et al

Lignin occludes polysaccharides Lignin Hemicellulose Cellulose

Effect of lignin content on enzymatic recovery of sugars from Miscanthus D Vrije et al (2002) Int J Hydrogen Energy 27,1381 Lignin Switchgrass composition cellulose Hemi cellulose

USDA Amber Waves 2007 Biofuels and food

Thow & Warhurst, 2007 (divide by 2.2 for break even oil price in $/bbl) Ethanol production cost per ton CO 2 equivalent emissions offset (not accounting for land use)

Food – the perfect storm? Population Food preferences Climate change Biofuels

Bioenergy – the climate protective domain Increase growth Increase efficiency of conversion to useful products Utilize sites where C loss from conversion is small in relation to bioenergy yield Utilize sites that are not needed for something else

Field, Campbell, Lobell TREE 2008

Land Type Area (Mha) Mean NPP (ton C / ha / yr) Total NPP (Pg C / yr) GlobalCrop1, Pasture3, Abandoned Potential from abandoned land Field, Campbell, Lobell TREE 2008

Land Type Area (Mha) Mean NPP (ton C / ha / yr) Total NPP (Pg C / yr) GlobalCrop1, Pasture3, Abandoned In Forest In Crop In Urban In Other From available abandoned land 0.8 Pg C x 2 g Plant/g C x 0.5 g top/g plant x 16 EJ/Pg = 13 EJ = 3% of current global energy system

Bioenergy Climate impact depends on pre-existing ecosystem Indirect as well as direct paths to carbon loss Natural NPP reasonable proxy for potential yield under ag management Available land resource limited –Quantity and quality Big potential in absolute terms But a small slice of present or future demand 35