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U-M study finds crop-based biofuels associated with net increase in GHGs; falsifying the assumption of inherent carbon neutrality

A new study from University of Michigan researchers challenges the assumption that crop-based biofuels such as corn ethanol and biodiesel are inherently carbon-neutral—i.e., that only production-related greenhouse gas (GHG) emissions need to be tallied when comparing them to fossil fuels.

In an open-access paper published in the journal Climatic Change, the researchers conclude that once estimates from the literature for process emissions and displacement effects including land-use change are considered, US biofuel use to date is associated with a net increase rather than a net decrease in CO2 emissions.

The study, based on US Department of Agriculture crop-production data, shows that during the period when US biofuel production rapidly ramped up, the increased carbon dioxide uptake by the crops was only enough to offset 37% of the CO2 emissions due to biofuel combustion over the period 2005-2013.

The use of biofuels to displace petroleum has been driven by public policies, including subsidies but most compellingly by regulations, notably the US Renewable Fuel Standard (RFS) and California Low-Carbon Fuel Standard (LCFS). Policy rationales include agribusiness income, energy security, oil depletion and greenhouse gas (GHG) mitigation.

The environmental justification rests on the assumption that, as renewable alternatives to fossil fuels, biofuels are inherently carbon neutral because the CO2 released when they are burned is derived from CO2 uptake during feedstock growth. That convention is premised on globally complete carbon accounting in which biogenic emissions are not counted in energy sectors when carbon stock changes are counted in land-use sectors. This assumption has been used in cap-and-trade programs and carbon taxes as promulgated to date, which address only fossil-derived CO2 emissions. However, errors arise when bioenergy is treated as carbon neutral in national and subnational policies, which do not impose globally coherent accounting that tracks all carbon stock changes. The carbon neutrality assumption is also embedded in lifecycle analysis (LCA), which traditionally focused only on production-related GHG emissions within a fuel’s supply chain.

… Thus, although it was proposed as an objective way to compare fuels, LCA has become a form of scenario analysis. However, it is inferior in this regard to integrated assessment modeling (IAM), which uses a biogeochemically and economically coherent analytic framework that LCA lacks. Moreover, as a static framework, it fails to reflect the stock-and-flow dynamics that are fundamental to bioenergy systems. Indeed, policy applications of LCA raise serious questions regarding the limitations of the method. Given such concerns, it is useful to analyze the situation by a method other than LCA.

—DeCicco et al.

The researchers applied Annual Basis Carbon accounting to investigate the changes in carbon flows directly associated with a vehicle-fuel system. Unlike LCA or other forms of carbon accounting used for climate policy to date, ABC does not treat biofuels as inherently carbon neutral; it tallies CO2 emissions on the basis of chemistry in the specific locations where they occur.

ABC accounting reflects the stock-and-flow nature of the carbon cycle,— i.e., that changes in the atmospheric stock depend on both inflows and outflows. LCA, on the other hand, focuses only on inflows (GHGs discharged into the atmosphere).

The system in the study was defined to include motor fuel consumption, fuel processing operations and resource inputs, including cropland for biofuel feedstocks.

Thus, instead of modeling the emissions, lead author Professor John DeCicco and his colleagues analyzed real-world data on crop production, biofuel production, fossil fuel production and vehicle emissions—without presuming that that biofuels are carbon neutral.

This is the first study to carefully examine the carbon on farmland when biofuels are grown, instead of just making assumptions about it. When you look at what’s actually happening on the land, you find that not enough carbon is being removed from the atmosphere to balance what's coming out of the tailpipe.

When it comes to the emissions that cause global warming, it turns out that biofuels are worse than gasoline. So the underpinnings of policies used to promote biofuels for reasons of climate have now been proven to be scientifically incorrect. Policymakers should reconsider their support for biofuels. This issue has been debated for many years. What’s new here is that hard data, straight from America’s croplands, now confirm the worst fears about the harm that biofuels do to the planet.

—John DeCicco

DeCicco’s co-authors include current and former students at the U-M School of Natural Resources and Environment and the U-M Program in the Environment, as well as a postdoctoral researcher at the Energy Institute. They are Danielle Yuqiao Liu, Joonghyeok Heo, Rashmi Krishnan, Angelika Kurthen and Louise Wang.

Some funding for the study was provided by the American Petroleum Institute.




Could it be that we have been had one more time by our industries-governments and that clean biofuels are not so clean.

Clean coal, clean blue NG and other clean burning fossil fuels are other industrial lies also supported by our governments?

Electric vehicles (BEVs/FCEVs) using clean REs only may be one of the only clean answer.


"Some funding for the study was provided by the American Petroleum Institute"

Nick Lyons

Better to use existing waste streams (municipal, industrial) than convert food crops to fuel crops.


"crop-based biofuels associated with net increase in GHGs"
Compared to neutral (none) of course they do, compared to refineries they are wonderful.


When the effect of crop-based biofuels on net fuel economy is incorporated, they are worse than refineries.

What we really need is the Ford-MIT ultraturbocharged engine (perhaps with the Nissan VCR system).  A few percent of 160-proof ethanol injected as an on-demand octane booster would do far more to improve fuel economy and reduce emissions than E10.  However, it would completely destroy gasohol as a farm-price support program— which is what it really is.


Wow, UM prof (well established petrol supporter) has found that ethanol fuel is not carbon neutral when used as an fuel. Also, if adding all the carbon emissions including biogeochemically and economically coherent analytic frameworks, the carbon emission is worse than plain gasoline.

These above statements read so damming, but what benchmark of carbon emission rates ethanol as neutral? None! The term is sometimes utilized to describe the gross biologics of ethanol per carbon cycle. Kind of like when we describe wind energy as free. The scientist falsely lead reader to believe ethanol carbon ratings leave out land use change penalties and process emissions.

The life cycle analysis does reduce emissions per the natural carbon cycle. What credible analysis would only rate ethanol per gross carbon additions? Your right a petrol advocate, that uses such tactic as a comparison to petrol since petrol has no offsets to reduce it's carbon rating.

Actually, the life cycle emissions are complex and all encompassing. The latest addition to the GW math is the albedo effect. The ethanol carbon ratings do include transportation, farm emissions, process, and distribution. Most GW ratings will have a asterisk that state if ethanol engine efficiency improvements were included a much better rating would ensue.

The GW emission rating of ethanol should be forward leaning as improvements are not stationary, but upon a positive glide path. Really, we should make an evaluation of what is possible in near term. The processing efficiency is rapidly improving and since this is the majority of emissions very important factor. At this period of time best estimates of miscanthus ethanol are negative carbon. The grass has much better rating than forest land since their is no natural rotting of bio matter emissions and the grass packs away much carbon in soil.

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