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Biofuels and climate: a simple but troubling view

John DeCicco's picture
, University of Michigan Energy Institute

Research Professor at the University of Michigan Energy Institute.

  • Member since 2018
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  • Mar 14, 2012

If biofuels benefit the climate, it’s not when they’re burned; those CO2 emissions are the same as from the fossil fuels they replace. Any potential benefit is due to the CO2 uptake when plants are grown. Society should maximize that uptake and, once carbon is absorbed, do everything possible to keep it from getting back into the air. This almost certainly means not burning biofuels.  

As a form of renewable energy, biofuels are promoted as a way to reduce excess emissions of carbon dioxide (CO2), the primary greenhouse gas (GHG) that is disrupting the earth’s climate. Ethanol and other forms of bio-based energy also find solid support as farm products and their firmest backing is found in states with strong agricultural interests. The desire to “rely on the Midwest, not the Mideast” makes boosting biofuels a patriotic quest. With environmentalists raising the green banner along side the red, white and blue of agribusiness and energy security, biofuels have enjoyed a political consensus as broad as ever seen on any issue in this day and age. When the Renewable Fuel Standard (RFS) was expanded to mandate 36 billion gallons of ethanol, biodiesel and other biomass-based fuels by 2022, the Senate vote was 86 to 6.

Nevertheless, the climate benefits of biofuels have been debated for many years. The discussions are often contentious, with warring studies that compare the carbon footprints of different fuels under competing assumptions. The passage of the RFS and its provisions for carbon footprinting (technically termed lifecycle analysis) and similar requirements in California’s Low Carbon Fuel Standard (LCFS) means that these long-running academic debates now take on high stakes commercially. Billions of dollars of investments have been made in new biorefineries, mainly for ethanol but also for biodiesel. Hundreds of millions of dollars of venture capital and taxpayer subsidy are being spent on the quest for next-generation biofuels in the hope that they can be made from non-food crops, tree plantations and forest trimmings, wastes, algae and even synthetic life forms being created in the lab.

The core of this debate and a basic tenet of the lifecycle view is the fact that the carbon in a biofuel was recently absorbed from the atmosphere and so exactly cancels out the CO2 released when the biofuel is burned. This “renewability shortcut” in carbon footprint calculations presumes that biofuels are inherently carbon neutral. As an accounting convention, it implies that if feedstocks are grown and converted into fuels efficiently enough, then replacing a fossil fuel with a renewable fuel such as ethanol from biomass cuts GHG emissions overall.

It’s the big “if” about the net GHG emissions of the biofuel production chain — from the need for land and nutrients to the emissions during processing, refining and distribution — that is so difficult to ascertain. In trying to patch over the carbon neutrality assumption, lifecycle analysis becomes inordinately complex and too unreliable to yield sound answers. A new paper concludes that evaluating biofuels through lifecycle analysis is a lost cause, overwhelmed by scientific uncertainties and undone by the intractable system boundaries involved when accounting for GHG impacts throughout the global and dynamic commodity markets that supply feedstocks and fuels. A legal critique of such flaws in carbon footprinting is one basis for the recent court decision blocking California’s LCFS.

There is an easier way to look at the issue and that is to focus not on the carbon neutrality of biomass, but rather on the fact that the CO2 released when burning a biofuel for energy is essentially the same as the CO2 released when burning an equivalent amount of fossil fuel. This simple function of chemistry bears emphasis because we’ve become so accustomed to thinking that the carbon in biofuels doesn’t count. In round numbers, burning a gallon of gasoline directly releases 19 pounds of CO2 and so does burning an equivalent amount of ethanol. As a finer point of chemistry, the exact numbers differ by 0.4 percent and similarly, the CO2 directly released by biodiesel differs from that of petroleum diesel by roughly one percent.

In short, the benefit of biofuels is not in the burning. The atmosphere is better off only if the growth of biofuel feedstocks pulls more CO2 from the air than happens when growing plants for other reasons. This perspective implies that the focus should really be on maximizing CO2 uptake by the biosphere and, once the carbon is fixed, doing everything possible to keep it from being re-emitted.

Pulling CO2 from the air is not easy. Doing so with chemical engineering is very difficult. Photosynthesis evolved to fix carbon, but exploiting it productively is resource intensive, requiring lots of land, water and nutrients. That’s the perennial challenge of sustainable agriculture, and large-scale agriculture is, after all, itself a net emitter of greenhouse gases. In a climate-concerned world, fixed carbon should be treated as a precious substance. It’s awfully hard to re-absorb and also tricky to sequester once it’s been combusted into CO2.

If one sets aside the carbon neutrality presumption and realizes that the immediate atmospheric impact of a carbon-based fuel is the same regardless of its origin, the following question comes to mind. Once CO2 has been fixed through carbon uptake, does it make sense to expend more energy and release more emissions to process it into biofuels, only to burn that hard-gained carbon and re-release it to the air?  

The answer will rarely be yes. That is a conclusion in line with the acknowledged value of reducing deforestation and seeking ways to rebuild terrestrial carbon stocks through forest regrowth and other natural area restorations that accumulate carbon. Given that bio- and fossil fuels emit the same CO2 when burned, one can more confidently counterbalance emissions with carbon offsets than with the huge uncertainties involved in modeling the carbon footprints of biofuels. Offset programs pay great attention to issues of verification, additionality, leakage and permanence. These challenges are best addressed by policies that focus on the locations where sequestration is enhanced or is at risk. It is futile to try to address them through complex lifecycle and econometric modeling of biofuels used far from the locations where CO2 uptake, sequestration and land-use activities occur.

A troubling implication is the need to reconsider efforts to synthesize biofuels from various forms of biomass. Rather than continuing the decades-long struggle to break down the cellulose and lignin that comprise the bulk of plants, or to bioengineer plants, algae or other life forms to increase their production of molecules amenable for making transportation fuels, it makes more sense to search for ways to keep carbon from turning into CO2 while finding other uses for the biomass.  

With agricultural and forestry wastes, for example, instead of pursuing the still largely quixotic quest to turn them into fuel, it may be better to develop chemical processes that maximize the fixed carbon residue while exploiting as much hydrogen as possible for energy. Carbon in a solid form or enriched in nonvolatile compounds is easier to dispose of than CO2. It might also be valuable as a construction material or basis for other long-lived products that keep the carbon out of the air. This means foregoing the copious combustion energy of carbon, so there’s an opportunity cost, but it may well be a more cost-effective way to limit emissions than all the processing involved in turning biomass into a convenient fuel that gets burned and releases CO2 anyway.

This simplified view of biomass and energy raises a lot of questions and provokes new research needs. It could spell an end to years of conventional but irresolvable thinking about biofuels, which as far as climate protection is concerned, may turn out to be but a long road to a dead end.  

Rick Engebretson's picture
Rick Engebretson on Mar 14, 2012

There are as many broad brush strokes in this article as there are in many corn ethanol promotions.

One fact is worth emphasizing; more carbon in more soil over more areas of the globe will likely feed more people better. “Biofuel,” (whatever is implied by the term) can be done well, or done badly. Being cast in such broad terms as above truly hurts opportunity to do it well.

Paul O's picture
Paul O on Mar 15, 2012

@John DeCicco,

The questions you’ve raised are very much worth asking:

If the Total amount of CO2 emitted from the production and burning of Bio-fuels is more than the CO2 removed from the atmosphere by the bio-fuel stock, then is the whole process actually doing what it’s meant to do?

Are we not better of just growing the Bio fuel stock or any other vegetation, without attempting to convert it to fuel, if the overall CO2 emissions are a net gain?

Should we not grow the bio-fuel stock purely for sequestration purposes, and find other means of providing for our liquid fuel needs?

Food for thought indeed.

Erich J. Knight's picture
Erich J. Knight on Mar 17, 2012

The Paleoclima­te Record shows agricultur­al-geo-eng­ineering is responsibl­e for 2/3rds of our excess greenhouse gases. The unintended consequenc­e; flowering of our civilizati­on. Our science has now realized these consequenc­es, developing a more encompassi­ng wisdom. Wise land management­, afforestat­ion and the thermal conversion of biomass can build back our soil carbon. Pyrolysis, Gasificati­on and Hydro-Ther­mal Carbonizat­ion are known biofuel technologi­es, What is new are the concomitan­t benefits of biochars for Soil Carbon Sequestrat­ion; building soil biodiversi­ty & nitrogen efficiency­, as a feed supplement cutting the carbon foot print of livestock & in situ remediatio­n of toxic agents, Modern systems are closed-loo­p with no significan­t emissions. The general LCA is: every 1 ton of biomass yields 1/3 ton Biochar equal to 1 ton CO2e, plus biofuels equal to 1MWh exported electricit­y, so each energy cycle is 1/3 carbon negative

Beyond Rectifying the Carbon Cycle, the same healing function for the Nitrogen and Phosphorou­s Cycles

CoolPlanet is gearing up to produce farm scale reactors , on skids, the tank ready fuel can cover all haulage and harvest operations.
CoolPlanet is cool far beyond the $1.00-$1.15 per gallon, because;
There is no fuel blending wall, the more you blend, the lower the C-foot print.
Is it fossil fuel ?…or is it biofuel? … only your radiocarbon isotope tester knows for sure.

Wee-Beastie Real estate at Land Rush Prices;
The farm scale reactors are producing a high surface area biochar, 600 sq meters / gram, Or, One ton of Char has a surface area of 148,000 Acres!!
Now for conversion fun: 148,000 Acres is equal to 230 square miles!! Rockingham Co. VA. , where I live, is only 851 Sq. miles
Now at the middle of research application rates of 1 lb/sq ft or 20 tons/acre, this yields 4,600 Sq miles of surface area per Acre. VA is 39,594 Sq miles. An eighth of Virginia in every acre.
What this suggest to me is a potential of sequestering virgin forest amounts of carbon just in the soil alone, without counting the forest on top.
CoolPlanetBiofuels’ Mike Cheiky presenting to a Google audience his company’s plans for “Negative-Carbon” biofuels, soil improvement, and poverty reduction.

Rick Engebretson's picture
Rick Engebretson on Mar 17, 2012

The first sentence is untrue. Bio based fuels are hydrogen saturated fuels, fossil fuels are carbon based up to almost pure carbon coal. The CO2 produced from combustion is absolutely not the same. Some very basic chemistry.

There are far more vexing problems emerging. The corn fertilizer problem is certainly one. Another is the use of pesticides and the not so newly linked destruction of pollinating insects, such as bees. Another is water.

We will be dealing with the food, energy, and water problem whether we want to or not. Whether we are competent or not.

Graeme Tychsen's picture
Graeme Tychsen on Mar 18, 2012

Our unwitting immersion in fossil energy, especially fossil oil, with its immense deployability, having presented us with an energy devouring world of centralised systems now sees us vainly and relentlessly coming up with ideas that could only come from the most sci-savvy civilisation in history, but really to no avail. It is the heavy, fixed pall of doubt of every prosposal to find the means to continue the punch for motion, to be viewed in the widest sense, the basis of the economic law of comparative advantage, the only way from subsistence existence, of fossil oil’s explosive combustion, through internal combustion engines, made of once generally abundant material (even metal in the public arena of the UK is more and more being scavenged), that is the alarming intractable problem. Presently our deludedly impregnable fossil world has one yawning achilles heel. Further, rather than using what power through fossil we have to turn matters around, we seem intent, albeit involuntarily, on increasing the energy requirement per person, of those enjoying an advanced standard of living, currently about 400X more than that of someone of the agricultural period.  Presently, those in the advanced category are soaring on an exploding global population and skyrocketing economic development of once impoverished nations.

Simon Friedrich's picture
Simon Friedrich on Mar 19, 2012

I agree with John DeCiccio that lifecycle analysis has no place in quantifying greenhouse gas emissions from carbon containing fuels such as biofuels. At best it measures the economic or social good of a product. Maybe Siemens can convince Germany and the European Union to start counting emissions from biofuels rather than assuming that these emissions are “carbon neutral” and can be ignored in inventories of greenhouse gas emissions.  

John DeCicco's picture
Thank John for the Post!
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