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.

When do biofuels really balance carbon?

The belief that biofuels are inherently carbon neutral rests on an assumption that the CO₂ absorbed when their feedstocks are grown balances out the CO₂ emitted when the fuel is burned. That's why it's said that biofuels recycle carbon, in contrast to fossil fuels' one-way flow of carbon into the atmosphere.

However, the extent to which CO₂ emissions actually get balanced needs to be verified, not just assumed, even as obvious as it may seem. A careful analysis shows that biofuel carbon flows balance out only under certain conditions. Moreover, those conditions are at best only partly met for the biofuels now being used. To see why, it is necessary to understand some fundamental concepts about CO₂ flows between the biosphere and atmosphere.

Scrutinizing the logic on biofuels

This post picks up a thread based on comments that Prof. Robert Brown and Prof. Bruce Dale made on my "Don't pitch low-carbon fuel ..." post. Both Robert and Bruce take strong exception to my analysis. They invoke the commonly made assumption that substituting a biofuel for a fossil fuel reduces net CO₂ emissions because biofuel use recycles carbon while fossil fuel use does not.

This widely used view of the biofuel lifecycle does not tell
the whole story.  [Image credit: www.EthanolRFA.org] 

Their argument is based on the following logic:

(1) Fossil fuels send old carbon on a one-way trip to the atmosphere, thereby increasing the amount of CO₂ in the atmosphere.

(2) Biofuels use carbon recently taken from the air that is then released back to the air, resulting in no net change in the amount of CO₂ in the atmosphere.

(3) Therefore, substituting a biofuel for a fossil fuel reduces the rate of CO₂ buildup in the atmosphere.

Although this basic analysis neglects processing emissions, we can leave those aside for the purpose of this discussion. They are not what's at the heart of the disagreement, and in any case processing emissions do get tracked by lifecycle models, e.g., as used in the RFS and LCFS. 

Don't tout low-carbon fuel; track real carbon instead

My recent studies expose the fallacies behind California's Low-Carbon Fuel Standard (LCFS) and similar provisions of the U.S. Renewable Fuel Standard (RFS). Such policies claim to reduce the carbon footprint of motor fuels, but are more likely to actually increase CO2 emissions.

I'm not alone in expressing such concerns. A paper whose authors include the original developer of the lifecycle analysis method that underpins the LCFS points out how such approaches can mislead policy makers. A recent World Resources Institute (WRI) report faults policies that promote biofuels and create an adverse "food vs. fuel" trade-off.

Among the objections to my criticism is that it is merely academic and fails to offer a constructive solution for the transportation fuel-related CO2 emissions that remain after improving vehicle efficiency and limiting travel demand.

Governor Arnold Schwarzenegger signing AB 32 on Sept. 27, 2006
(Source: Getty Images via Zimbio)

In California, however, the answer is right under policy makers' noses. The Global Warming Solutions Act [Assembly Bill (AB) 32] caps carbon emissions statewide, and starting this year also places transportation fuels under the cap. AB 32 is the best climate protection program established anywhere to date, and with a technical correction plus expanded provisions for carbon offsets, it would be an ideal policy for addressing fuel-related CO2 emissions.

Why bad bookkeeping undermines fuel policies

There's a problem with the policies now imposed on transportation fuels in an attempt to control CO2 emissions. The issue has to do with how carbon is counted when the policies are defined.

Good accounting needs to reflect the fact that motor fuels are liquids that contain carbon as their molecular backbone. By nature, liquids flow. That's one main reason why they are so valuable for fueling cars, trucks, ships and planes. Carbon flows with the fuels, and it's the rate at which the carbon flows to and from the atmosphere in the form of CO2 that matters for global warming.

Note the "to and from" in the previous sentence. A big focus of climate policy is reducing CO2 emissions, e.g., reducing the rate at which carbon flows into the air due to energy use. But the from part is also important, and in fact, the CO2 problem is best described as an imbalance in the global carbon cycle due to human activities that cause carbon to flow into the atmosphere faster than natural processes can remove it.

The Global Carbon Cycle
(Source: www.esrl.noaa.gov Carbon Cycle Toolkit)

The adjoining figure illustrates the global carbon cycle. As suggested by the relative thickness of the arrows depicting the flows, the overall cycle is much larger than the excess from fossil fuel use. In round numbers, the natural CO2 flow amounts to circulation of about 200 PgC/yr (petagrams, i.e., 1015 grams, or billion of metric tons, of elemental carbon per year) between the atmosphere and the earth's surface (both land and sea). The total flow into the atmosphere from fossil fuel consumption has been steadily climbing and is now about 10 PgC/yr. Roughly another 1 PgC/yr of emissions are due to deforestation. (The latest data can be found at the Global Carbon Project.)  

The carbon cycle matters a lot when biofuels enter the picture. To protect the climate, biofuels must increase the from part of the carbon cycle; that is to say, they have to increase the net rate at which CO2 is removed from the atmosphere. After all, they don't decrease the to part of the cycle because simple chemistry tells us that a given biofuel emits essentially the same amount of CO2 as the fossil fuel it replaces. As I've put it elsewhere, if biofuels have a benefit, it's not when they're burned.

Bread & Circuses vs. Getting the Prices Right

Two researchers just published an analysis showing something that many casual observers have long realized about the political challenges of using taxes to address externalities. Liddle & Lung (2015) find that countries whose citizenries consume a lot of fuel tend to tax fuel at lower rates than countries with relatively lower consumer demand for fuel. In other words, the nations having a greater need to "get the prices right" through some form of consumption tax are, politically speaking, less likely to pursue the types of taxation that economists would recommend.

The paper is:

Liddle, Brant and Lung, Sidney, The Endogeneity of OECD Gasoline Taxes: Evidence from Pair-Wise, Heterogeneous Panel Long-Run Causality Tests. Transportation Research A: Policy and Practice, 73: 31-38, 2015. DOI: 10.1016/j.tra.2014.12.009; available at SSRN: http://ssrn.com/abstract=2557780

CO2 sequestration more challenging than thought

Recent MIT simulations suggest that when CO2 is injected underground into saline aquifers, much less of it may solidify than most carbon capture and storage (CCS) studies have assumed. The implications are that such CCS may be less stable than hoped and also that the capacity for CO2 sequestration would be much lower than past research has calculated (see "Sequestration on shaky ground" from MIT News).

This form of CCS is not very relevant for mitigating emissions from liquid fuel use. However, the hypothetical "BECCS" (bioenergy with CCS) systems that some analysts have highlighted as a potential source of so-called low-carbon liquid fuels would also face such limitations.

Are falling fuel prices good or bad?

Yesterday in Automotive News, Richard Truett penned a piece titled, "Why falling fuel prices are bad, bad news."  His point was that lower pump prices make fuel-efficient vehicles a harder sell, risking the billions of dollars that automakers have recently invested in hybrids, electric cars and other alternatives as well as lightweight materials and advanced combustion engines.

The argument that high fuel prices are good for cutting oil use and carbon emissions follows directly from basic economics. Mr. Truett hopes that oil prices will head back up this year and, guided by economics, many conservation advocates have long called for higher taxes to address oil-related concerns. I'm certainly not one to argue with those principles, but I also believe that lower fuel prices are on balance a very good thing for American consumers and the economy.