Clarifying the biofuel carbon offset

Components of the biofuel carbon offset. The gross offset comprises the whole pie; the net induced offset is highlighted in blue. Based on stock-and-flow modeling of a corn ethanol scenario. 

The carbon neutrality of biofuel combustion is sometimes discussed in terms of its fossil fuel offset, i.e., the fossil carbon emissions that are avoided when it is used in place of a fossil-based fuel such as conventional gasoline. The offset occurs because the biofuel contains biogenic carbon recently removed from the atmosphere by photosynthesis instead of fossil carbon that was buried underground. 

As the U.S. Environmental Protection Agency (EPA) stated in its Renewable Fuel Standard (RFS) regulation, "For renewable fuels … the carbon emitted as a result of fuel combustion is offset by the uptake of biogenic carbon during feedstock production." As explained below, this assumption of a feedstock offset is not generally true. In particular, it fails for fuels derived from commodity crops, as is the case for most biofuels now produced at commercial scale. 

Substituting biofuel for fossil fuel triggers changes in several different carbon flows into and out of the atmosphere. The technical literature has examined these effects using complex methods such as consequential lifecycle analysis (CLCA) and integrated assessment modeling (IAM). However, the key concepts can be explained using a relatively simple stock-and-flow model. 

I built such a model to illustrate the main carbon flow effects associated with biofuel use. Although its parameters were chosen from the literature on corn ethanol, it deliberately omits the ancillary, production-related GHG emissions that are the traditional focus of LCA. The objective is to offer insights rather than generate specific numerical findings.  

Researchers have identified three market-mediated effects that contribute to offsetting a biofuel's biogenic emissions. They are induced by the marginally higher crop prices that result as biofuel feedstock demand is added to demand for food and feed:  

• Decreased food consumption due to the higher prices; this can be termed the deprivation effect (although some of it may result from more efficient use of crop harvests).  
• Increased crop yields as farmers in response to the higher prices, comprising what is known as the intensification effect and thereby increasing the rate of net carbon uptake. 
• Increased overall harvests obtained by planting more cropland, a response known as the extensification effect and which involves land-use change (LUC) that may impact carbon-rich natural lands. 

The extensification-driven LUC can cause a large short-term release of carbon into the atmosphere, incurring what is known as carbon debt. By reducing the area of natural land that is actively storing carbon, it can also result in foregone sequestration that undermines the net offset. The deprivation effect reflects the "food versus fuel" problem and contributes to the offset by reducing carbon consumption by the food system. That implies a lower rate of CO2 emissions from respiration and thereby effectively raising the rate of net carbon uptake by the biosphere. Although intensification does not have the adverse impacts of these other two effects, it can result in higher GHG emissions from greater use of fertilizers, irrigation and other ancillary farming activities (as commonly evaluated by LCA, but omitted for the conceptual analysis described here). 

In addition to these effects on biogenic carbon flows, the decreased petroleum demand as biofuel displaces fossil fuel can decrease petroleum prices and cause a rebound effect of increased fuel demand and its associated CO2 emissions in other markets, further undermining the net offset. 

The pie chart above summarizes how these carbon flow changes influence the biofuel offset. The entire pie represents a complete balancing ("neutralization") of a biofuel's biogenic emissions through gains in net carbon uptake. This constitutes the gross offset. It has three components that fill the pie including the cross-hatched portions. They are depicted here based on nominal parameter values for a stock-and-flow scenario detailed in the paper on which this post is based. Deprivation accounts for 33% of the gross offset (pink slice); intensification accounts for 15% (green); and the remaining 52% is from extensification (beige), reflecting the area of new cropland put into production to supply both biofuel production and food system consumption. 

The cross-hatched portions show the countervailing effects of foregone carbon sequestration, which erodes 8% of the gross offset, and petroleum market rebound, which erodes 20% based on the assumed parameter values. That leaves the net induced offset, amounting to 72% of the gross offset. It determines the long-term net emissions reduction obtained when biofuel replaces fossil fuel. 

Biofuels can be seen as carbon neutral to the extent that their production induces a gross offset. Explicitly tracking carbon flows with a stock-and-flow model makes it clear that "neutralizing" biofuel CO2 emissions involves several distinct mechanisms rather than a presumptive feedstock offset. Moreover, the net induced offset is less than a full offset even before considering a biofuel's non-biogenic, production-related GHG emissions as evaluated by LCA. Stock-and-flow modeling also highlights the strong time dependence of a biofuel's impact on atmospheric carbon when land-use change is involved, showing how the net induced offset influences the slope of the decline in the atmospheric carbon stock that pays down carbon debt. 

This illustrative analysis pertains to a crop-based biofuel such as corn ethanol. For other biofuels, such as those derived from biomass waste, different mechanisms could be involved, but a stock-and-flow analysis would still apply and their net offset would still be less than a full because of the rebound effect. 

Visualizing the time-varying carbon impact of biofuels

Several years ago I did a post entitled "When do biofuels really balance carbon?" At issue is the belief that biofuels are inherently carbon neutral. That assumption is typically justified in terms of a feedstock offset, i.e., that a biofuel's end-use and other biogenic CO2 emissions are fully balanced by CO2 uptake during photosynthesis when their feedstocks are grown. However, that proposition is not generally true. A more correct understanding is that the CO2 emitted from biofuel use can be partly balanced by gains in net CO2 uptake in several locations (not just where feedstock is grown) over a possibly long period of time.

In the biofuel literature, this understanding of biofuel-related carbon flows was developed through consequential lifecycle assessment (CLCA) modeling, which is quite complicated and hardly transparent. However, the key insights can be seen with relatively simple stock-and-flow modeling. The outcome of such an exercise is described here.

The following figure shows illustrative results for a scenario of biofuel use as shown in the bottom panel (c) of the figure. This model input assumes that corn ethanol use ramps up to 13 billion gallons per year (Ggal/year) over a 10-year period (2005-2015) and then remains constant thereafter. The analysis was done in units of teragrams of carbon (Tgc); 13 Ggal/year of ethanol corresponds to 20 Tgc/year on a carbon (not CO2) mass basis.

Changes over time in (a) atmospheric carbon and (b) net carbon emissions due to (c) biofuel use. Shown relative to a fossil-fuel reference case; units are teragrams of carbon (Tgc). 

The middle panel (b) shows the effect on net carbon emissions. Emissions rise sharply as ethanol use ramps up, reflecting the release of terrestrial carbon stocks as natural lands (such as tropical forests or grasslands) are cleared, directly or indirectly, to make way for new cropland. Such land-use change is triggered by the additional crop production needed for biofuels. Once biofuel use stops rising (after 2015 in the scenario modeled), net carbon emissions fall below the fossil fuel reference case. This emission reduction, which amounts to roughly 17 Tgc/year for the case shown here, reflects the net induced offset due to biofuel use. It is less than a full offset of the biofuel's associated biogenic emissions and results from changes in several carbon flows economically induced by biofuel use as explained in a subsequent post.

The top panel (a) shows the resulting change in atmospheric carbon which, as a stock, is the integral of the net emissions flow of panel (b). Atmospheric carbon rises above the fossil fuel reference level as biofuel increases, reflecting the carbon debt from the biofuel-related land-use change. Atmospheric carbon begins decreasing once biofuel use stops increasing, falling below the reference level after 2054. That is 48 years after the first year of modeled biofuel use (2006) in the scenario shown here, reflecting the time it takes to pay back the carbon debt and highlighting the nearly five decade lag before the biofuel use achieves a net CO2 reduction.

This greatly delayed climate mitigation is obscured by most LCA studies, which smooth over important time-varying effects when reducing their results to carbon intensity values (e.g., grams of CO2-equivalent per megajoule of fuel). The system dynamics revealed by stock-and-flow modeling emphasize that, although biofuels may offer a long-term net carbon reduction, they can make matters worse before they get better.

Cellulosic ethanol's highly subsidized failure

Actual U.S. production of cellulosic ethanol and other cellulosic liquids compared to the targets for cellulosic biofuels specified in the Renewable Fuel Standard

Cellulosic ethanol, once a great green hope for cutting petroleum use and CO2 emissions, has been a bust. The chart above compares the volume of cellulose-based liquid biofuels (largely ethanol) actually used in the United States to the targets for such fuels set by Congress when it expanded the Renewable Fuel Standard (RFS) in 2007. Note the logarithmic scale on the vertical axis; the gap between promise and reality is so large that actual production would be barely visible on a linear scale. 

The fuel has been delivered at levels of no more than about 0.1% of (three orders of magnitude less than) the volumes on which the RFS was premised [1]. This chart does not include cellulosic biogas, which EPA re-classified to qualify for RFS compliance purposes and has seen recent production of around 500 million ethanol-equivalent gallons. However, such "renewable natural gas" is not in the spirit of the law, which envisioned liquid biofuels that could be readily used in motor vehicles. The 2019 RFS target for cellulosic biofuels was 8.5 billion gallons, set to reach 16 billion gallons by 2022. But in 2019, before the pandemic-related drop-off in 2020 for nearly all forms of energy, only 9.8 million gallons of cellulosic ethanol were tallied by EPA.  

Reconsidering bioenergy

Accelerated restoration in progress at the Malheur National Forest, Oregon  [photo: U.S. Forest Service] 

Protecting the Earth's climate takes on greater urgency every day. The vast majority of carbon dioxide (CO2) and other climate-wrecking greenhouse gas (GHG) emissions comes from the unmitigated use of fossil fuels. But that doesn't mean that every form of alternative energy is helpful for the planet. Case in point: bioenergy, such as liquid biofuels to replace oil or forest products to replace coal.

Indeed, using biomass for energy at large scales does not belong on the short list of actions to take for climate protection. This is the conclusion of a commentary by Bill Schlesinger and myself just published in the Proceedings of the National Academy of Sciences. Given the real-world limitations of not only technology but also land-use governance, we argue that the priority policymakers have given to promoting bioenergy is profoundly misplaced.

Breaking down biofuels analysis

Debates about the merits of biofuels have gone on for at least a generation. Over time, one might think that the accumulation of data would resolve key issues, especially those about biofuels and global warming. Nevertheless, the arguments not only persist but have become even more heated.

What has taken things to a new level of contention is that some researchers (myself included) are now rethinking the heart of the matter, namely, the belief that biofuels are inherently carbon neutral. This is the assumption that the CO2 emitted when biofuels are burned does not lead to a net increase in emissions because the carbon in the biofuel is recycled during feedstock growth. My new paper, "Methodological issues regarding biofuels and carbon uptake" published in the journal Sustainability, breaks this aspect of the debate down to its bare essentials.

Biofuels vs. Biodiversity and the Need to Think Beyond Carbon Neutral

Seminar given at the University of Michigan, Thursday, February 8, 2018, as part of the 2016-2018 "Beyond Carbon Neutral" seminar series.

Download the presentation slides [PDF]

ABSTRACT

Just over a decade ago, policymakers gave a big boost to biofuels through the Renewable Fuel Standard (RFS) and similar policies. These policies included sustainability provisions for protecting sensitive lands; the intent was to spur the production of advanced biofuels that would be sustainable in many ways including low CO2 emissions. Now, new studies appear each year revealing the destruction of diverse habitats as biofuel production amplifies the global demand for land. There have also been multiple bankruptcies of highly-subsidized advanced biofuel operations. What went wrong and how can we find a better path forward?

Carbon balance effects of biofuel expansion

The 4th biennial America's Grasslands Conference organized by the National Wildlife Federation was held in Fort Worth, Texas, on 14-16 November 2017. What follows is the narrative with key slides from my presentation in the session on "The Ethanol Mandate as a Driver of Land Conversion and Carbon Emissions." 

I imagine that you have often heard that ethanol and other biofuels are "clean and green" compared to ordinary gasoline. Even if not perfect, aren't biofuels better than petroleum because they recycle carbon from the atmosphere instead of getting it from under the ground? That makes them inherently carbon neutral, many people believe.

Unfortunately, that belief is quite misleading. Take, for instance, the claim that corn ethanol reduces greenhouse gas emissions by 43% compared to gasoline, as given by a recent USDA study (which is critiqued here). That value is based on computer modeling and the assumption that biofuels fully recycle carbon is hard-coded into the model. However, when using field data to evaluate how much CO2 is actually recycled, it turns out that such modeling is off base, and not by just a small amount. In fact, biofuels fall so far short of being truly carbon neutral that they cause higher rather than lower CO2 emissions than petroleum fuels.

A new and deeper wrinkle in the biofuel debate

Two short articles just published by the journal Climatic Change highlight the divide in scientific thinking about the effect of biofuels on CO2 emissions. A commentary by Robb De Kleine and colleagues at Ford Motor Company criticizes a paper on the topic published last year by myself and colleagues at the University of Michigan. My response to their commentary explains why I believe that our approach is correct, in contrast to the established lifecycle analysis method that our critics say is the best way to address the question.

Cropland adjoining patches of forest. All arable land
removes carbon from the atmosphere at varying rates. 

This quarrel reflects a new stage in the long-running debate because it does not involve disputes about net energy use or even the food-versus-fuel and land-use change issues raised over the past decade. It is instead a disagreement about the core assumptions to use when examining the question, particularly whether or not biofuels should be treated as inherently carbon neutral. That's the assumption that the CO2 emitted when biofuels are burned does not count because it is biogenic, i.e., newly removed from the atmosphere when feedstocks are grown. My work challenges this assumption, showing that it only holds under certain conditions. De Kleine and colleagues defend the assumption, arguing that it is true unconditionally.

The disagreement is not merely academic. Because new oil production technologies have expanded the supply of economically attractive fossil-based liquid fuels, the business case for biofuels rests increasingly on their value for mitigating CO2 emissions. The stakes are high for both the biofuels industry and for policies to address global warming.

Biofuel Research vs. Mandates: House Science Committee Hearing

John DeCicco speaking before the U.S. House of Representatives Committee on Science, Space and Technology, where the Subcommittees on the Environment and on Energy held a joint hearing entitled "Examining Advancements in Biofuels: Balancing Federal Research and Market Innovation" on Tuesday, July 25, 2017. What follows is the statement delivered at the hearing. 

I wish to thank the chairs, ranking members and other members of the Committee and Subcommittees for the opportunity to testify.

The question being addressed today, that of the right balance between fundamental scientific research and government intervention in the marketplace, is crucially important. The focus on biofuels is telling because it involves so many aspects of the question. Indeed, federal biofuels policy provides a morality tale of how things go wrong when the right balance is not maintained.

Before delving into the problems, however, I want to emphasize the importance of maintaining a robust federal investment in research across all fields of study. Funding for science is crucial to maintain American leadership and foster the innovation that leads to high-quality job growth. Federal support for university research is especially crucial for training a new generation of Americans who can fill those jobs. 

A to-the-point radio interview on biofuels and climate

As a guest yesterday on the WEMU (89.1 FM from Eastern Michigan University) "Issues of the Environment" segment, I answered host David Fair's questions about how our recent work differed from the established lifecycle analysis methods used to analyze the greenhouse gas emissions impacts of biofuels.

The resulting interview has great questions from David and clear explanations from myself about why the results of government modeling of the issue are misleading and why, as far as climate is concerned, it's better to repeal biofuel policies and focus on reforestation and other ways to remove carbon from the air and sequester it on land.

Morning Edition: Issues of the Environment 

U-M Researcher Calls For End To Current Biofuel Policy In The U.S.

http://wemu.org/post/issues-environment-u-m-researcher-calls-end-current-biofuel-policy-us

By DAVID FAIR • WEDS 01 FEB 2017

In August of 2016,  University of Michigan Energy Institute scientists, led by John DeCicco, released an 8-year study.  It estimated powering an American vehicle with ethanol made from corn increased carbon pollution more than using gasoline.  In this week's "Issues of the Environment,” David Fair talks with Professor DeCicco about the findings and what it means to future policy. 

IMAGE CREDIT: DREW FROM ZHRODAGUE / FLICKR.COM

Listen Here [10:09 mp3 link] 

Separating fact from fiction in the newest U.S. federal ethanol study

Debates about the merits of biofuels have been going on for at least a generation. My favorite clip from the early, oil-crisis era ethanol push was Nicholas Wade’s article, "Oil pinch stirs dreams of moonshine travel," published by Science in June 1979. Save for one topic, the terms of the debate — the costs of producing biofuels, whether ethanol took more energy to make than it delivered, the extent to which it really helps energy security, the hope for cellulosic biofuels and the food-versus-fuel dilemma — were the same nearly forty years ago as they are today.

Global warming is the topic not on the table then that is so important now. The effect of biofuels on greenhouse gas (GHG) emissions is the focus of many recent studies. To compare fuels according to their GHG impact, policymakers have adopted a form of computer modeling known as lifecycle analysis (LCA). A new report from the U.S. Department of Agriculture (USDA) is the latest LCA study to claim significant GHG reductions from the use of corn-based ethanol, concluding that it has net GHG emissions 43 percent lower than those of petroleum gasoline. Those results are similar to the findings of lifecycle modeling from Argonne National Laboratory (ANL), on which this latest USDA study heavily relies.

My own work has long come to an opposite conclusion. It shows that the use of biofuels (both ethanol and biodiesel) makes GHG emissions worse that they would otherwise be. This finding is not based on computer modeling, but relies instead on field data to assess the real-world CO2 flows involved when substituting biofuel for fossil fuel.

Carbon balance effects of real-world biofuel use

Most of the debate about the environmental merits of biofuel use has been based on lifecycle analysis (LCA). Also known as life-cycle assessment, carbon footprint analysis, "cradle-to-grave" analysis, or (in the case of motor fuels) "well-to-wheels" analysis, LCA is a method for adding up all of the impacts of interest associated with a product. It includes the effects of producing a product and its component materials, associated shipping and packaging effects (as relevant), the use of the product and any related disposal effects. For assessing climatic impacts, LCA tallies the greenhouse gas (GHG) emissions associated with the production, use and disposal of the product. When the product is a motor fuel, the numerical result of such LCA modeling is called the fuel's "carbon intensity," as calculated for California's Low-Carbon Fuel Standard (LCFS), for example.

A cornfield does not absorb CO2 from the atmosphere
any more quickly when it is used to make ethanol than
when it is grown for food or feed. This basic fact of 
carbon mass balance is ignored by the lifecycle studies
that claim climate benefits for biofuels. 

The question, "how does the overall emissions impact of using a biofuel such as ethanol compare to that of a fossil fuel such as gasoline?" seems straightforward, and sounds like something that LCA can answer. However, that question is actually ill-posed scientifically speaking. In other words, when one looks carefully at what actually happens when a given biofuel substitutes for a fossil fuel, it turns out that LCA cannot give a straightforward, unambiguous answer. Properly qualified, the answer will always be, "it depends." And it doesn't just depend on the particular fuel and how it is produced; it also depends on the design of the LCA model and the assumptions it invokes.

U.S. biofuel consumption chart through 2015

Just to provide an updated picture of the rise in U.S. biofuel consumption, here's a chart based on the latest annual data from EIA's Monthly Energy Review (MER). 

As of calendar year 2015, U.S. ethanol consumption was 13.9 billion gallons per year, up from 1.7 billion gallons in 2000. In 2000, biodiesel consumption was below the level of significance for EIA reporting (i.e., statistically zero relative to overall U.S. motor fuel use). Biodiesel consumption reached 1.5 billion gallons in 2015, and so total biofuel consumption amounted to 15.4 billion gallons that year.

For context, U.S. motor gasoline consumption was 140 billion gallons and distillate fuel oil (which is mostly but not all highway diesel) was 61 billion gallons last year.

In terms of carbon, biofuels accounted for 4.7% of total direct CO2 emissions from the U.S. transportation sector in 2015.

A short URL for embedding this chart is: https://goo.gl/rM5EpM. If you use it, please credit this blog. The source data can be downloaded as Tables 10.3 (for ethanol) and 10.4 (for biodiesel) from the Renewable Energy section of EIA's MER webpage.

A-\R-\Corn+soy+biofuel_stats

Latest tweak to U.S. biofuel mandate is politically correct and ecologically cruel

EPA's new Renewable Fuel Standard (RFS) proposal modestly increases the amount of biofuel that America's cars and trucks have to consume next year but still keeps the total renewable fuel mandate below the Congressionally scripted target.

In the plan released on May 18, ordinary corn ethanol gets a 300 million gallon boost, biodiesel is bumped up by 100 million gallons and other so-called advanced biofuels see a 200 million gallon increase compared to last year's regulation. Nevertheless, the proposed 18.8 billion gallon total remains significantly lower than the 24 billion gallon goal for renewable fuel in 2017 that Congress wrote into law back in 2007.

EPA's approach reflects a compromise worked out last year after several tortuous years of regulatory delay. This "politically correct" strategy has the agency taking a middle road that balances the money-making interests of the biofuel industry and the corn and soybean lobbies against the engineering and economic realities that render ethanol and biodiesel such inferior motor fuels. Reactions to the proposal were predictable. The renewable fuel lobby and its allies complain "that's not enough" while the oil industry and other critics say "that's too much" biofuel.

House Oversight Testimony on the RFS

This post is a transcript of my oral testimony at the U.S. House of Representatives as delivered on March 16, 2016. 

I wish to thank the Chairs, Ranking Members and other members of the committee and subcommittees for inviting me to today’s hearing.

My name is John DeCicco and I am a research professor at the University of Michigan Energy Institute. My main focus is transportation fuel use and its environmental impact. I hold a doctorate in engineering from Princeton University and have worked on America's energy challenges for nearly 40 years, including 21 years at environmental organizations before returning to academia in 2009.

My recent research has included scientifically rigorous evaluations of the Renewable Fuel Standard (RFS) and other policies that promote biofuels such as ethanol and biodiesel. RFS proponents claim that the policy reduces CO2 emissions. I have found that it does not. In fact, from its inception, the RFS has increased rather than decreased the amount of CO2 entering the atmosphere compared to petroleum fuels such as gasoline.

Questions and responses on RFS testimony

House Science Committee Hearing on the RFS, November 3, 2015
(photo credit: Michael A. Waring) 

Following the recent hearing on the Renewable Fuel Standard (RFS) held by the House Science Committee, the subcommittee chairs asked me to respond to some questions for the record, following up on my testimony at the hearing. Here are the questions and an abbreviated version of the answers, summarizing my full written response. 

In his testimony, Mr. Coleman referenced cellulosic ethanol that is "129 times better than gasoline on carbon emissions." Based on your research, is this a reasonable claim?

No, that is not a reasonable claim. Such assertions are based on paper studies of hypothetical ethanol production methods. There is indeed a literature on the subject that applies lifecycle analysis (LCA) to proposed cellulosic ethanol production methods and projects that the resulting systems would not only fully offset tailpipe CO₂ emissions but also offset other CO₂ emissions such as those from fossil-based electricity generation.

However, as pointed out in my testimony (and in papers explained elsewhere on this blog), the LCA methods used to justify such claims are scientifically incorrect. Moreover, the cellulosic processing methods involved remain speculative as far as any meaningful commercial-scale operation is concerned. In short, claims of biofuels that achieve a more than 100% reduction in carbon emissions are rooted in flawed analysis of fantasy fuels. 

Testimony on the RFS

Here's my statement at today's House hearing on the RFS; see links at the end to access the written testimony and related videos. 

My research shows that the Renewable Fuel Standard, or RFS, has been harmful to the environment from its inception. Now, ten years after the 2005 Energy Policy Act, the program has resulted in higher CO2 emissions than would have occurred otherwise. It also harms the environment in other ways. Sadly, the adverse impacts of the RFS have grown worse since it was expanded by Energy Independence and Security Act (EISA) of 2007.

The notion that renewable fuels readily reduce CO2 is based on a scientifically incorrect understanding of carbon neutrality. Only under certain conditions does substituting a biofuel for a fossil fuel neutralize the CO2 leaving the tailpipe. For that to occur, harvesting the feedstock must significantly increase how rapidly cropland absorbs CO2 from the atmosphere on a net basis. That condition is not met for the corn ethanol mandated by the RFS. It might be satisfied for cellulosic feedstocks, but once properly evaluated, the gains may not be as great as advocates assume.

Thinking Beyond Carbon Neutral

Global climate change is a defining challenge of the 21st century and efforts to address it have many dimensions. Reducing greenhouse gas (GHG) emissions through higher energy efficiency, using solar, wind and nuclear energy, deploying carbon capture and storage (CCS), reducing deforestation, reducing methane emissions and minimizing other causes of excessive radiative forcing are all important. No one option will suffice and it is crucial to integrate technology solutions with policy drivers.

Because the carbon dioxide (CO2) emitted by fossil fuel use is the largest source of anthropogenic GHG emissions, the climate challenge is often characterized as the need to "decarbonize" the economy by eliminating fossil fuels. However, carbon is literally the fuel of life; the natural carbon cycle annually circulates twenty times as much carbon as released from fossil fuels and the majority is biogenic carbon fixed through photosynthesis. Although rapid release of fossil carbon is the primary cause of rising atmospheric CO2 concentrations, the real problem is an imbalance in the carbon cycle rather than fossil fuel use per se. Thus, the real need is to bring the carbon cycle into balance and eventually restore a global net carbon sink.

The mistaken modeling behind biofuel boosters' emissions claims

Arguments about the pros and cons of biofuels such as ethanol have gone on for many years. The latest debates pertain to whether proposals to limit the ramp-up of the Renewable Fuel Standard (RFS) would result in higher or lower emissions of carbon dioxide (CO2) and other climate-disrupting greenhouse gases.

This week Environmental Protective Agency (EPA ) Administrator Gina McCarthy tweeted the benefits of biofuels: 

and signaled the agency's intent to further raise the RFS volumetric mandate: 

At the crux of the issue is the ability to determine the “carbon footprint” of biofuels using computer models. These models, such as the GREET model developed by Argonne National Laboratory in Illinois, use what are known as lifecycle assessment techniques that claim to account for all of the emissions associated with producing and using a fuel. GREET modeling is the basis for assertions by BIO (the Biotechnology Industry Organization) that the RFS has reduced carbon emissions since it was passed in 2005. It is also the basis for the recent University of Illinois statement that the proposed RFS limits would increase CO2 emissions as much as putting nearly one million more cars on the road. 

Bringing biofuels back to earth

After all that's been written about the pros and cons of biofuels over the years, it's fair to ask whether there's anything left to say. It turns out that there is, and a new insight comes from evaluating what actually happens on the earth, that is, on the land where the plants used to make biofuels are grown.