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Ever since the 1973 oil embargo, U.S. energy policy has sought to replace petroleum-based transportation fuels with alternatives. One prominent option is using biofuels such as ethanol in place of gasoline and biodiesel instead of ordinary diesel.
Transportation generates one-fourth of U.S. greenhouse gas emissions, so addressing this sector’s impact is crucial for climate protection.
Many scientists view biofuels as inherently carbon-neutral: they assume the carbon dioxide (CO2) plants absorb from the air as they grow completely offsets, or “neutralizes,” the CO2 emitted when fuels made from plants burn. Many years of computer modeling based on this assumption, including work supported by the U.S. Department of Energy, concluded that using biofuels to replace gasoline significantly reduced CO2 emissions from transportation.
Our new study takes a fresh look at this question. We examined crop data to evaluate whether enough CO2 was absorbed on farmland to balance out the CO2 emitted when biofuels are burned. It turns out that once all the emissions associated with growing feedstock crops and manufacturing biofuel are factored in, biofuels actually increase CO2 emissions rather than reducing them.
The biofuel boom is a climate blunder
Federal and state policies have subsidized corn ethanol since the 1970s, but biofuels gained support as a tool for promoting energy independence and reducing oil imports after the September 11, 2001 attacks. In 2005 Congress enacted the Renewable Fuel Standard, which required fuel refiners to blend 7.5 billion gallons of ethanol into gasoline by 2012. (For comparison, in that year Americans used 133 billion gallons of gasoline.)
In 2007 Congress dramatically expanded the RFS program with support from some major environmental groups. The new standard more than tripled annual U.S. renewable fuel consumption, which rose from 4.1 billion gallons in 2005 to 15.4 billion gallons in 2015.
Our study examined data from 2005-2013 during this sharp increase in renewable fuel use. Rather than assume that producing and using biofuels was carbon-neutral, we explicitly compared the amount of CO2 absorbed on cropland to the quantity emitted during biofuel production and consumption.
Existing crop growth already takes large amounts of CO2 out of the atmosphere. The empirical question is whether biofuel production increases the rate of CO2 uptake enough to fully offset CO2 emissions produced when corn is fermented into ethanol and when biofuels are burned.
Most of the crops that went into biofuels during this period were already being cultivated; the main change was that farmers sold more of their harvest to biofuel makers and less for food and animal feed. Some farmers expanded corn and soybean production or switched to these commodities from less profitable crops.
But as long as growing conditions remain constant, corn plants take CO2 out of the atmosphere at the same rate regardless of how the corn is used. Therefore, to properly evaluate biofuels, one must evaluate CO2 uptake on all cropland. After all, crop growth is the CO2 “sponge” that takes carbon out of the atmosphere.
When we performed such an evaluation, we found that from 2005 through 2013, cumulative carbon uptake on U.S. farmland increased by 49 teragrams (a teragram is one million metric tons). Planted areas of most other field crops declined during this period, so this increased CO2 uptake can be largely attributed to crops grown for biofuels.
Over the same period, however, CO2 emissions from fermenting and burning biofuels increased by 132 teragrams. Therefore, the greater carbon uptake associated with crop growth offset only 37% of biofuel-related CO2 emissions from 2005 through 2013. In other words, biofuels are far from inherently carbon-neutral.
Carbon flows and the ‘climate bathtub’
This result contradicts most established work on biofuels. To understand why, it is helpful to think of the atmosphere as a bathtub that is filled with CO2 instead of water.
Many activities on Earth add CO2 to the atmosphere, like water flowing from a faucet into the tub. The largest source is respiration: Carbon is the fuel of life, and all living things “burn carbs” to power their metabolisms. Burning ethanol, gasoline, or any other carbon-based fuel opens up the CO2 “faucet” further and adds carbon to the atmosphere faster than natural metabolic processes.
Other activities remove CO2 from the atmosphere, like water flowing out of a tub. Before the industrial era, plant growth absorbed more than enough CO2 to offset the CO2 that plants and animals respired into the atmosphere.
Today, however, largely through fossil fuel use, we are adding CO2 to the atmosphere far more rapidly than nature removes it. As a result, the CO2 “water level” is rapidly rising in the climate bathtub.
When biofuels are burned, they emit roughly the same the amount of CO2 per unit of energy as petroleum fuels. Therefore, using biofuels instead of fossil fuels does not change how quickly CO2 flows into the climate bathtub. To reduce the buildup of atmospheric CO2 levels, biofuel production must open up the CO2 drain – that is, it must speed up the net rate at which carbon is removed from the atmosphere.
Growing more corn and soybeans has opened the CO2 uptake “drain” a bit more, mostly by displacing other crops. That’s especially true for corn, whose high yields remove carbon from the atmosphere at a rate of two tons per acre, faster than most other crops.
Nevertheless, expanding production of corn and soybeans for biofuels increased CO2 uptake only enough to offset 37% of the CO2 directly tied to biofuel use. Moreover, it was far from enough to offset other greenhouse gas (GHG) emissions during biofuel production from sources including fertilizer use, farm operations, and fuel refining. Additionally, when farmers convert grasslands, wetlands, and other habitats that store large quantities of carbon into cropland, very large CO2 releases occur.
Mistaken modeling
Our new study has sparked controversy because it contradicts many prior analyses. These studies used an approach called lifecycle analysis, or LCA, in which analysts add up all of the GHG emissions associated with producing and using a product. The result is popularly called the product’s “carbon footprint.”
The LCA studies used to justify and administer renewable fuel policies evaluate only emissions – that is, the CO2 flowing into the air – and failed to assess whether biofuel production increased the rate at which croplands removed CO2 from the atmosphere. Instead, LCA simply assumes that because energy crops such as corn and soybeans can be regrown from one year to the next, they automatically remove as much carbon from the atmosphere as they release during biofuel combustion. This significant assumption is hard-coded into LCA computer models.
Unfortunately, LCA is the basis for the RFS as well as California’s Low-Carbon Fuel Standard, a key element of that state’s ambitious climate action plan. It is also used by other agencies, research institutions, and businesses with an interest in transportation fuels.
I once accepted the view that biofuels were inherently carbon-neutral. Twenty years ago I was lead author of the first paper proposing use of LCA for fuel policy. Many such studies were done, and a widely cited meta-analysis published in Science in 2006 found that using corn ethanol significantly reduced GHG emissions compared to petroleum gasoline.
However, other scholars raised concerns about how planting vast areas with energy crops could alter land use. In early 2008 Science published two notable articles. One described how biofuel crops directly displaced carbon-rich habitats, such as grasslands. The other showed that growing crops for biofuel triggered damaging indirect effects, such as deforestation, as farmers competed for productive land.
LCA adherents made their models more complex to account for these consequences of fuel production. But the resulting uncertainties grew so large that it became impossible to determine whether or not biofuels were helping the climate. In 2011 a National Research Council report on the RFS concluded that crop-based biofuels such as corn ethanol “have not been conclusively shown to reduce GHG emissions and might actually increase them.”
Uncertainties inspire a new look
These uncertainties spurred me to start deconstructing LCA. In 2013, I published a paper in Climatic Change showing that the conditions under which biofuel production could offset CO2 were much more limited than commonly assumed. In a subsequent review paper I detailed the mistakes made when using LCA to evaluate biofuels. These studies paved the way for our new finding that in the United States, to date, renewable fuels actually are more harmful to the climate than gasoline.
It is still urgent to mitigate CO2 from oil, which is the largest source of anthropogenic CO2 emissions in the United States and the second-largest globally after coal. But our analysis affirms that, as a cure for climate change, biofuels are “worse than the disease.”
Reduce and remove
Science points the way to climate protection mechanisms that are more effective and less costly than biofuels. There are two broad strategies for mitigating CO2 emissions from transportation fuels. First, we can reduce emissions by improving vehicle efficiency, limiting miles traveled, or substituting truly carbon-free fuels such as electricity or hydrogen.
Second, we can remove CO2 from the atmosphere more rapidly than ecosystems are absorbing it now. Strategies for “recarbonizing the biosphere” include reforestation and afforestation, rebuilding soil carbon and restoring other carbon-rich ecosystems such as wetlands and grasslands.
These approaches will help to protect biodiversity – another global sustainability challenge – instead of threatening it as biofuel production does. Our analysis also offers another insight: Once carbon has been removed from the air, it rarely makes sense to expend energy and emissions to process it into biofuels only to burn the carbon and re-release it into the atmosphere.
John DeCicco is a research professor at the University of Michigan. This post originally appeared at The Conversation.
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12 Comments
"...There are two broad
"...There are two broad strategies for mitigating CO2 emissions from transportation fuels. First, we can reduce emissions by improving vehicle efficiency, limiting miles traveled, or substituting truly carbon-free fuels such as electricity or hydrogen.."
Basically the world would have to pull everyone, except for the farmers, from rural areas into cities so that personal transportation will be 100 percent electric. Yes, this even includes our favorite editor Martin. Highways would be populated solely by self-driving trucks burning diesel or some combination of diesel/electric. Transportation between cities will be via rail or air only. You don't want people driving themselves between the cities because that increases wear on the EV's. EV's will be mostly recyclable. We will always wear hemp clothing because you know, synthetic fabrics require fossil fuels and cotton requires a lot of fertilizer. Since we need to pack as many people into a minimum space the single family dwelling and 2-4 unit dwelling will disappear. Everyone, save for the elites, will live in dense pack multi-story housing. To keep everyone from going crazy the State will encourage weekend trips to the countryside.
OR
We could follow Dr. Hawking's advice and get off this rock.
My two cents. Sarcasm and all. ;P
Urbanity not a prerequisite for electrified transportation.
The year on year improvements in battery technology (and price) means that EVs are no longer relegated to the 50 mile/day commuter car or electrified light rail. On a lifecycle basis a 200 mile range EV is already cheaper than a fossil burner even if charged solely by photovolatics. Both EVs and PV are on steep cost decline trajectories as manufacturing volumes increase, and there are no natural resource or other barriers to ubiquity.
If properly compensated for the value to the grid (which involves some re-writing of electricity markets), smart EV chargers can make electrified transportation even cheaper still.
EV drive trains experience very minimal wear & tear compared to fossil burners, the largest factor being battery degradation over time. And EVs are already largely recyclable (and recycled), since even used EV batteries retain value as grid storage (on either side of the meter), at a price point lower than new grid batteries. Nissan is already involved with commercialized grid storage products in Europe, re-using Leaf batteries that are beyond their useful life as transportation batteries.
Short haul electrified light aircraft are coming too, but it'll be at least another decade or two.
Most people don't see it coming yet, but at least two countries will disallow sales of internal combustion light trucks & cars by 2030, one of them (India) in a high growth automotive market. According to the manufacturers' projections by 2025 it will be hard to buy a new car or light truck in the US that doesn't plug in, even if it has an internal combustion engine.
In the intermediate term, long haul trucks in the US will more likely be using natural gas or natural gas/electric hybrids than diesel/diesel-electric. We're really just one oil price spike away from the tipping point (remember $100/bbl oil?) They're already here, but at the moment only cost-neutral over a typical 4-5 year lifecycle at currently lower diesel pricing, limiting a ramp up in market penetration.
https://freightliner.com/trucks/natural-gas/
http://www.greencarreports.com/news/1094087_why-arent-natural-gas-powered-long-haul-semi-trucks-selling-better
Given how cheap natural gas BTUs can be under new production technology it doesn't take a doubling of oil prices to tip the economics strongly in favor of natural gas for long haul trucking. And from the non-CO2 air pollution content point of view it's a hands-down win to go with natural gas burners.
@Dana Dorsett .
Ahh yes. I forgot about Nat Gas. Drivers in Europe have been able to convert their vehicles to Nat Gas for years. Much cleaner burning than diesel. Vehicles burning Nat Gas can go thousands of miles longer between oil changes than diesel. A++
On the other hand diesel has more energy per volume and can amass significant efficiency gains if pollution controls are relaxed (EGR and Urea Injection). Sure they'll be dirtier, but they'll save on fuel and they should run at max efficiency since the roads will be clear of light trucks/cars.
Wood vs Ethanol
Can the author (or someone more enlightened than myself) explain if all biomass can be critiqued in this manner? For example, is burning wood equally bad to ethanol? In Burlington, VT we like to say that our grid is 100% renewable, but if the wood chip electric generation plant we have is a net producer of GHG that makes things look a lot less rosy. On a smaller scale, what about efficient wood burning stoves?
Response to Sam Beall
Sam,
Many people have attempted to answer the questions your raise. The topic is controversial, and not all experts agree.
GBA has published many articles on the topic. You may want to start by reading the articles below.
Do Wood-Burning Power Plants Make Sense?
NRDC: Burning Trees to Make Electricity is an ‘Environmental Disaster’
Biomass Electricity Production: How Green Is It?
Should Green Homes Burn Wood?
Wood gets complicated
In nearby and similarly forested Massachusetts back in 2010 the state commissioned a study to determine the break-even points when using wood biomass fuels in generators against fossil fuels. The full 182 page report lives here:
http://www.mass.gov/eea/docs/doer/renewables/biomass/manomet-biomass-report-full-hirez.pdf
The executive summary lives here:
http://www.mass.gov/eea/docs/doer/renewables/biomass/manomet-biomass-report-executivesummary.pdf
The upshot is that forestry practices and thermal efficiency matter (a lot!), and there is no case where using wood for power generator fuel can hit the necessary thermal efficiency to be carbon neutral (or lower carb than burning natural gas) other than combined heat & power (CHP) cogenerators. But with reasonable forestry practices using wood strictly for heating fuel can sometimes make it.
Massachusetts regulations based on that study disallows renewable energy credits (RECs) for generators operating at less than 40% thermal efficiency and only half a REC for those operating between 40-60% thermal efficiency, with a full REC for 60% or higher. There are no simple cycle generators that can even hit the 40%, but CHPs sometimes can.
Most EPA rated woodstoves can hit north of 75% efficiency, but if the comparative fossil fuel is condensing natural gas at 90% efficiency it's probably not break-even within a reasonable time frame. If the comparative fossil fuel is #2 oil burned 85% efficiency it probably does.
[edited to add] The summary of "Carbon Debt Payoff" time in Figure 3 of the executive summary indicates that thermal wood takes only 5 years to become carbon neutral against #6 oil burned for thermal output (which is similar enough to #2 oil), but 24 years against thermal uses of natural gas. While 24 years is a long time, it's still close enough to being a reasonable payback time relative to cumulative carbon emissions and forest wood growth lifecycles. The 90+ years for wood fired power to "payoff" is not. [end edit]
But most dumb 25% thermal efficiency biomass generators in New England burning forest residues aren't really helping the carbon situation- the stuff is better off left as sequestered soil carbon.
I happen to live in an forest parasite insect quarantine zone (Asian Longhorned Beetle), and any wood leaving the quarantine zone A: must be chipped to less than 1/2" and B: shipped in sealed containers to a biomass burner facility. Given how rapidly the stuff would build up in this urban-forest I have no qualms about using it in an EPA woodstove at 75%+ thermal efficiency rather than chippin' & shippin' to the biomass burner down the road to be burned at 25% thermal efficiency.
In the UK they give green credits (where none are really due) to coal fired powerplants modified to use sustainably grown wood pellets as at least part of the fuel mix, and it has become a big export biz for parts of the southeastern US. The scale of those operations pale in comparison to the current fleet of biomass burning generators in New England.
thanks Dana & Martin
Thanks for taking the time.
woody biomass
It's telling that the Jacobson plan deliberately leaves out biomass in its attempt to chart a plausible path to a renewable energy future paid for out of avoided costs.
I believe this was out of concern over the effects of soot. Biomass is really hard to burn cleanly, and even gassifying boilers emit concerning levels of PM 2.5--the really tiny particles that travel long distances, contribute to global warming, and are increasingly understood to be a significant public health problem. EPA has good data on this and has been tightening regs around wood stoves for that reason, to the wrath of much of the industry.
And as Dana points out forestry practices also matter a great deal in this picture. Unless strong measures are taken, exploiting woody biomass on a larger scale is likely to cause significant disruption to the health of forest ecosystems that are already stressed in a number of ways. Nutrient export is one concern.
So unfortunately woody biomass has some pretty heavy strikes against it when you look beyond the simplistic notion of carbon neutrality.
Response to Dana
" Both EVs and PV are on steep cost decline trajectories as manufacturing volumes increase, and there are no natural resource or other barriers to ubiquity."
I've read that Lithium is in relatively short supply and that much of it is controlled by a potential economic and military adversary, China. Are we jumping out of one geopolitical frying pan (the mid east) into the far east geopolitical fire?
Your information on lithium is not correct.@ Curt Kinder
The largest readily accessible lithium deposits are in Bolivia (and not being exploited at scale), but the largest currently developed producers are (in descending orde) in Australia Chile & Argentina. China is a distant 4th place in lithium mining currently. But it's not a rare element, and developing new mines in the US (currently #8) would not be difficult if the sole operating mine in the US(in Nevada) isn't able to keep up with local demand in the face of a worldwide cartel or something. Afghanistan also has lexploitable lithium deposits. Australia's output dwarfs the rest, and 13,400 metric tons last year. (China's output was only 2300 metric tons.)
Lithium ion is not the only potential EV battery, it just happens to be the most developed due to advances in energy density and cyling longevity developed during the 1990s for portable electronics (phones & lap top computers.) Aluminum battery technology shows some potential for gaining high energy, but it's not yet been commercialized. In the event of a lithium shortage the other chemistries can rise pretty quickly.
What does the author mean by carbon-free?
The final clause of the third paragraph from the end of this article contradicts most of what has come before. "There are two broad strategies for mitigating CO2 emissions from transportation fuels. First, we can reduce emissions by improving vehicle efficiency, limiting miles traveled, or ***substituting truly carbon-free fuels such as electricity or hydrogen.***"
Neither electricity nor hydrogen falls freely from the sky and into transportation vehicle fuel tanks. In the current situation, supplying a car with either electricity or hydrogen has a significant carbon footprint, on average. Often from processing/burning fossil fuels or biomass. The quoted sentences put forward the same error that the author decries in most of this article- that it is inaccurate to make trivial assumptions about the greenhouse gas impacts of different technologies. Lack of emissions at the vehicle does not equate to "truly carbon free", just as carbon-sequestering tree growth doesn't equal carbon-neutral biofuel energy production. At the moment, the average electric car, charged from the grid, puts out more carbon per mile traveled than an efficient car burning gasoline.
C uptake of 49 Teragrams...
CO2 release of 132 Teragrams...
Yes, 49 Teragrams is 37% of 132 Teragrams.
But!
CO2 has 2 oxygen atoms attached to it.
C weighs 12.0107 and CO2 weighs 44.01 (no units needed, it is their relative weight)
So 132 Teragrams of CO2 is really only 36 Teragrams of C
(very basic science)
So, Apples to Apples (carbon atom to carbon atom)...
C uptake of 49 Teragrams
C release of 36 Teragrams
So, according to the above numbers more carbon was sequestered than released. But who knows how they got their numbers in the first place (and could the author have gotten this far on such a fundamental/basic blunder?).... And it doesn't matter. If the Carbon is not sequestered into a stable form it will most likely break down back into CO2 in short order anyway... the Carbon on our earth's surface constantly cycling between biomass and CO2. A carbon neutral exchange.
The way I understand it...
The earth used to have an atmospheric CO2 level of around 4000 ppm... About 10 times that of our current levels. But slowly, over many many millions of years, small amounts of partially broken down biomass left the earth's surface carbon cycle and was deposited (sequestered) into what is now our fossil fuel deposits.
The theoretical "crisis" we face today is based on a "sudden" influx of CO2 into the atmosphere from the extraction and burning of of the FOSSIL FUELS. And this new and sudden influx of carbon into our carbon cycle does seem to pose some very real threats.
What is "Carbon Neutral"?
If an activity burns FOSSIL FUEL there is a net increase of new C into the environment.
If an activity sequesters C into a stable (non-biodegradable) there is a net decrease of C in the environment.
Burning fossil fuels (bad)
Sequestering carbon into stable carbon storage (good)
If it doesn't involve either of these things I would think it should be called "carbon neutral".
How did things get so convoluted?
How can we find any solutions, when people make simple things so complicated?
What is the above article talking about? I don't know? Too much gibberish for me to pick apart in a comment box... and maybe I'm the one who is completely off base.
I feel that one of us, either myself or the author, has lost touch with reality.
Please let me know if/how the interpretation of how I see the current CO2 crisis is flawed.
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