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Researchers argue crop-based biofuels only show GHG savings because of LCA accounting flaw; the need for “additional” biomass

In an invited opinion paper published in the journal GCB Bioenergy, Kevin Smith from the University of Edinburgh and Tim Searchinger from Princeton University argue that current Life Cycle Analysis (LCA) models indicate that crop-based biofuels generate greenhouse gas (GHG) savings compared with fossil fuels only because the models ignore the emissions of CO2 from vehicles burning the biofuels without determining if the biomass is “additional”.

Additional biomass is biomass from additional plant growth or biomass that would decompose rapidly if not used for bioenergy. The models also underestimate the ultimate emissions of N2O from nitrogen fertilizer use, the authors suggest.

In a world that needs to produce more food while reducing emissions from both land-use change and nitrous oxide, it would be rather surprising to discover benefits from biofuels that use much of the world’s best cropland and crops with high nitrogen demand.

...The proper focus of biofuels policy should be on the generation of additional biomass from waste feedstocks, or high-yielding bioenergy crops with low nitrogen demand on land that is capable of generating such yields but now produces little biomass for humans, carbon sequestration or nature.

—Smith and Searchinger

LCA models for biofuels include calculations of the GHG emissions—including CO2and N2O—from the manufacture of the fertilizers and pesticides used in crop production; from fossil fuel used in the transport of fertilizer to the farm, farming operations and transport of the crop to the biofuel refinery; and from the refining process. These LCAs do not count the CO2 emitted by combusting biomass, and they nearly always assume a very small conversion rate of nitrogen to N2O, the authors note, posing the question as to whether these estimated reductions in emissions are real.

Where then do LCAs find the GHG reductions? They do so in critical part by ignoring the carbon emitted as CO2 from the exhaust pipes of vehicles that use biofuels, as well as the CO2 emitted by fermentation. In the case of ethanol, that CO2 is equal to 107 g MJ-1, which by itself is roughly 25% more than the entire lifecycle emissions of petrol according to typical estimates. The key question is the extent to which ignoring these very real releases of carbon is legitimate.

To the advocates of biofuels, this credit is self-evident because the growth of the grain or other plants used for the biofuel absorbs the same amount of carbon as that emitted by refining and burning the fuel. By this theory, plant growth ‘offsets’ the emissions from combustion.

That can be true, but a critical requirement for any offset is that it be additional. Biofuels cannot claim a credit for plant growth that would occur anyway. Certainly, biofuels save emissions from burning fossil fuels, but if all they do is substitute emissions from burning biomass, that does not by itself provide any benefit unless the biomass is better than the fossil fuel; and for it to be better in an emissions-related sense, the biomass must be ‘additional’. Biofuels can only reduce CO2 in the atmosphere if their generation results either in more CO2 absorbed from the atmosphere, or less CO2 emitted to it in some other way.

—Smith and Searchinger

The authors provide several examples of ways to obtain greenhouse gas benefits from biofuels:

  • Plant otherwise fallow land for biofuel crops. The added growth absorbs additional CO2, and thereby offsets the emissions from combustion.

  • Planting new forests (putting leakage aside), and storing more carbon above ground. Another legitimate offset occurs if biofuels use forest residues that would otherwise decompose and give off their carbon to the air, and the offset results from the reduction in carbon emitted from the forest floor.

However, when biofuels take feedstocks from a central storage of crops that farmers would grow anyway, they do not provide any offset through direct additional plant growth. In this case, the LCAs that automatically ignore the CO2 emitted by vehicle exhaust pipes are not only incomplete, they have no direct justification for doing so. And what happens when farmers clear forests, savannahs or grasslands to plant biofuel crops? The biofuel crop absorbs CO2, yet does so at the expense of losing carbon stored in vegetation and soils, and perhaps losing ongoing carbon sequestration as for- ests continue to grow. The problem is not that biofuels reduce GHG emissions, and land-use change increases them; the problem more accurately in such a case is that biofuels result in no positive land use or other market-based change that leads to greenhouse gas reductions in the first place.

—Smith and Searchinger

The overestimation of bioenergy LCAs becomes increasingly magnified when the omission of CO2 is combined with the underestimation of nitrogen emissions from fertilizer application. According to lead author Keith Smith, “Emissions of N2O from the soil make a large contribution to the global warming associated with crop production because each kilogram of N2O emitted to the atmosphere has about the same effect as 300kg of CO2.” He notes that several current LCAs underestimate the percentage of nitrogen fertilizer application that is actually emitted to the atmosphere as a GHG. The authors claim that the observed increase in atmospheric N2O shows that this percentage is in reality nearly double the values used in the LCAs, which greatly changes their outcome.


  • Smith, K. A. and Searchinger, T. D. (2012), Crop-based biofuels and associated environmental concerns. GCB Bioenergy. doi: 10.1111/j.1757-1707.2012.01182.x

  • Timothy D Searchinger (2010) Biofuels and the need for additional carbon. Environ. Res. Lett. 5 024007 (10pp) doi: 10.1088/1748-9326/5/2/024007

  • Helmut Haberl, Detlef Sprinz, Marc Bonazountas, Pierluigi Cocco, Yves Desaubies, Mogens Henze, Ole Hertel, Richard K. Johnson, Ulrike Kastrup, Pierre Laconte, Eckart Lange, Peter Novak, Jouni Paavola, Anette Reenberg, Sybille van den Hove, Theo Vermeire, Peter Wadhams, Timothy Searchinger (2012) Correcting a fundamental error in greenhouse gas accounting related to bioenergy, Energy Policy, Volume 45, June 2012, Pages 18-23, doi: 10.1016/j.enpol.2012.02.051


Henry Gibson

The official US government figures show that about 120 units of maize ethanol energy are produced by using 100 units of fossil fuel. If permanent, non fuel, trees were grown with the same solar input and nutrients and water then at least 120 units of CO2 would be removed from the air as is the case with maize. Since only the grain is used and the fermentation process also releases CO2, as mentioned, then perhaps 360 or more units of CO2 is stored in permanent trees which could be stored for eons in salt mines when dead.

Bio-fuels for aircraft and automobiles must be eliminated until each government that allows or requires the use of bio-fuels can assure the world that all bio-fuels will be produced within their own borders under strict CO2 accounting.

Massive areas in the US states of Alaska, Washington and Oregon plus others; can be reforested to remove CO2 from the air at far lower costs than the production of ethanol. WaterBoxx technology from GROASIS could even be used in more difficult areas.

Many automobiles run on methane, natural gas, and many more could. Methane use in automobiles would reduce CO2 release at lower cost more than any other automotive program. Most of the new LNG carriers run on methane at times and other ships are also using LNG at times.

Liquid Helium containers can be shipped by lorry across the US to their destinations, so there is no reason to not be able to mostly power all diesel locomotives and lorries with easier to handle LNG most of the time.

This comment ends with the statement usually put at the first: Bio-fuels destroyed the forests of the UK, US, Spain, Italy, North Africa, etc. hundreds of years ago if not thousands. There is not enough land for their production in any country or the world. ..HG..

A Facebook User

It also is interesting to note that, this is happening at the cost of Production of Food. as Economics work out & the returns on Bio Fuel crops improves many farmers & corporations might take up to growing Such crops instead of food based, in turn worsening the already bad food crisis's in many parts of the world.


You want to build up a National Woodpile Reserve and store it in salt mines?.. now we are getting desperate.

Randy Dutton

Several other aspects are missing.
1. Ethanol is very destructive to open-cycle engines and legacy vehicles. How much more carbon is emitted by poorly running engines, or in having to produce replacement vehicles;
2. Water vapor constitutes 95% of GWG. Since marginal farmland often is used to grow feedstock, considerably more irrigation, fertilizer, pesticide, herbicides are used. So biofuel feedstock growing raises global humidity and the warming effect;
3. N2O is extremely corrosive. By damaging equipment through corrosion, replacement equipment is more frequently needed, thus increasing energy and resource requirements.

As I wrote in The Carbon Trap, ethanol is one of the worst possible fuel choices. It's subsidized use is a scam.

Randy Dutton

While methane may burn cleaner, it also is 28 times more effective as a GWG than CO2. It oxidizes in 7-9 years do the use of natural gas creates 160% more global warming effect than CO2, which has an average life of 100 years before being absorbed. Promoting methane over coal or oil is a red herring. It doesn't reduce global warming increases.


A progressive but accelerated switch to BEVs and 5-minute chargers would negate the need for fossil and bio-fuels and get rid of a lot of pollution and other negative effects from ICEs + stop importing high cost crude and associated Oil wars..

Roger Pham

Very good points, Randy, to put everything in perspective.

The intensive irrigation in mechanized farming to feed our appetite for meat and poultry has a very serious yet under-recognized effect of GW. To produce 1 lb of beef requires 7-8 lbs of corn meal which produces even much larger amount of cellolusic waste. The cattle produce methane which has very high GHG index 28 x that of CO2. The use of irrigation in otherwise semi-arid lands no doubt has excerbated GW as well.

Only cellulosic bio-wastes should be used to make synthetic fuels, not dedicated fuel crops.

Methane leaks from the methane economy can be substantial contributor to AGW that can offset the lower CO2 emission in NG power plants. Furthermore, the sulfates from coal combustion can increase cloud formation that can help reduce GW, not that coal combustion is anymore acceptable, due to other pollutants from coal-fired power plants.

Only a totally-renewable-energy economy and a mostly vegan diet can offfer any real hope of combating GW. A high-fiber, low-sugar, whole-grain vegan diet can greatly reduce the incidences of obesity, diabetes, heart disease, cancer, premature aging, and a whole host of autoimmune diseases that have been escalating our health care costs. Somehow modern human beings have done it all wrong, inspite of all the research data, knowledge, information technology, and all the wonderful modern biomedical technologies.


Dutton... you're crazy.  H2O is far less effective a GHG than CO2 and CH4, so even if it is 95% of the mass of GHGs it's a far smaller fraction of the effect.  There's also the little detail that when it gets cold, the H2O rains out!  The more CO2, CH4, N2O, SF6, etc. that you've got, the more H2O stays in the air.

As for the faulty LCA of biofuels, all I can say is that it argues that the point of the effort was to discredit the best real alternatives to coal, oil and gas:  nuclear energy.


Progressive electrification of all (man-made) machines and HVAC is part of the final solution. Production of all the extra clean e-energy required can easily be done with with Nuclear-Wind-Solar-Hydro-Geothermal-Waves facilities.

Burning Coal, NG/SG, Fossil fuels, Bio-fuels and Bio-mass will have to be phased out.

Farms are best used to feed people directly or indirectly.

Forests are best used to produce wood for shelters, furniture, tools, toys etc.

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