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A liquid biofuels primer: Carbon-cutting hopes vs. real-world impacts

Harvested sugarcane in Karnataka, India.

Harvested sugarcane in Karnataka, India. A majority of biofuels are sourced from food crops, such as corn and sugarcane. India, along with Brazil and the U.S., announced ambitious plans earlier this year for a global biofuels expansion. Image by Timor Kodal via Flickr (CC BY-SA 2.0).

  • Liquid biofuels are routinely included in national policy pathways to cut carbon emissions and transition to “net-zero.” Biofuels are particularly tasked with reducing emissions from “hard-to-decarbonize” sectors, such as aviation.
  • Three generations of biofuel sources — corn, soy, palm oil, organic waste, grasses and other perennial cellulose crops, algae, and more — have been funded, researched and tested as avenues to viable low-carbon liquid fuels. But technological and upscaling challenges have repeatedly frustrated their widespread use.
  • Producing biofuels can do major environmental harm, including deforestation and biodiversity loss due to needed cropland expansion, with biofuel crops sometimes displacing important food crops, say critics. In some instances, land use change for biofuels can add to carbon emissions rather than curbing them.
  • Some experts suggest that the holy grail of an efficient biofuel is still obtainable, with much to be learned from past experiments. Others say we would be better off abandoning this techno fix, investing instead in electrifying the transportation grid to save energy, and rewilding former biofuel croplands to store more carbon.

As climate change has escalated over the decades, the demand for efficient liquid biofuels, especially to power the transportation sector, has grown more urgent, placing increased pressure on fragile ecosystems, even leading to outright bans.

Three generations of biofuels have been explored — with corn, soy, palm oil, grasses, algae and many other organic sources tried — but with most failing to fully live up to their promise. Still, biofuels remain a go-to climate solution for policymakers who view them as a green, carbon-cutting transition route to wean the world off fossil fuels.

Globally, investment in liquid biofuels hovered around $4 billion over the past decade, doubling in 2021 to more than $8 billion, according to the International Energy Agency (IEA), and more is needed to unlock the potential of “advanced biofuels,” it states. Over the years, a range of government policies has subsidized or supported the industry to the tune of billions of dollars in some cases. Recently, the U.S. government’s Sustainable Aviation Fuel Grand Challenge, for example, pledged around $4.3 billion to support research and help fuel producers develop clean biofuels.

Despite these efforts, three stumbling blocks have kept some biofuels from going mainstream and others mired in controversy: thorny technological problems, the inability to achieve cost-efficient upscaling, and environmental harm (ranging from deforestation to pollution).

An ethanol production plant in Indiana, U.S.
An ethanol production plant in Indiana, U.S. Debate over whether biofuels truly provide climate benefits continues, with various studies achieving contradictory results. Image by cassini83 via Wikimedia Commons (Public domain).

A study published in Biological Conservation in March found that the production and expansion of ethanol corn and soy crops in the U.S. can be linked to a range of “negative environmental outcomes.” These include “degraded water quality, increased water use, increased greenhouse gas emissions, and loss or degradation of wildlife habitat,” which can impact endangered species,” according to the paper.

“We found that land use changes associated with biofuel production are highly likely to adversely affect imperiled wildlife that should be protected under the U.S. Endangered Species Act,” Tyler Lark, the study author and a researcher at the Nelson Institute for Environmental Studies at the University of Wisconsin-Madison, told Mongabay in an interview.

The study identified specific endangered animals put at risk from ethanol production, including birds such as the whooping crane (Grus americana) and yellow-billed cuckoo (Coccyzus americanus); the rusty patched bumble bee (Bombus affinis); the Topeka shiner (Notropis topeka), a species of minnow; and the purple bankclimber (Elliptoideus sloatianus), an endangered mussel, among others.

Lark urges “further research and consultation among responsible [U.S.] agencies to mitigate the potential effects on listed [endangered] species and their habitats.”

“We often think about the potential for adverse impacts abroad; like tropical deforestation in the Amazon,” Lark continued. “But really, what we’ve seen from our research [on biofuels] over the last few years is that we need to be concerned about these impacts right here at home, too.”

Whooping Cranes in Nebraska.
Demand for land to produce biofuel crops could impact endangered species in the U.S., according to researcher Tyler Lark. Further studies are needed, he notes, but conservation deserves greater attention when considering biofuel policies. Image by Ronnie Sanchez/USFWS via Flickr (CC BY 2.0).

Three generations of biofuel boom and bust

Liquid biofuels aren’t new. Cars first began to run on a blend of bio-based ethanol on a large scale in the 1970s, with several experimental organic fuels going boom and bust over the decades. But as the need to decarbonize becomes ever more dire, biofuels have gained in importance again and again, with nations, companies and researchers all backing various sources.

Over the years, biofuels have evolved through three generations — each with its advantages and disadvantages, and each seeing cycles of boom and bust.

First Generation biofuels (dating roughly from the 1930s) include bioethanol and biodiesel sourced from corn, soy, oil palm and other crops, virgin vegetable oil, or animal fats. Second Generation biofuels (dating from the 1990s) are made from biomass-based non-food crops including grasses and various waste streams, while Third Generation biofuels (first researched in the 1970s and ’80s) are derived from algae.

None of these generations has so far produced a major bioenergy breakthrough that is clearly environmentally beneficial. Instead, the latest report by the U.N. Intergovernmental Panel on Climate Change (IPPC) urges that the cohort of liquid biofuels be chiefly “targeted to difficult-to-electrify sectors,” warning that all “face substantial challenges related to their lifecycle carbon emissions.”

The difficult-to-electrify sectors include shipping, aviation and “heavy-duty land transport” (such as trucks), with the world primarily benefiting in the “short and medium term” from organic liquid fuels as a fossil fuel transition. Global transportation today remains addicted to fossil fuels, with that sector responsible for up to one-quarter of humanity’s greenhouse gas emissions.

In 2021, global demand for liquid biofuels stood at an estimated 159.2 billion liters (42 billion gallons) according to the International Energy Agency (IEA); the majority are sourced from food crops, such as corn and sugarcane, while waste materials such as used cooking oil were the main non-food feedstocks.

Despite these volumes, production and use both need to expand and diversify greatly to reach their much-touted sustainable energy production potential, according to some experts. In the same year, biofuels (mostly those of the first generation) fed just 3.6% of total global transport energy demand; that needs to climb to 15% to meet climate goals. Aviation use, currently hovering at 0.1% biofuel use, is expected to reach just 5% by 2030.

To move things ahead, India, Brazil and the U.S., announced ambitious plans earlier this year for a global biofuels expansion. Together, these countries are already among the top biofuel users and account for the largest growth in the transport sector. Experts, however, caution that sustainability of biofuels is highly dependent on the feedstock used and any growth should not come at the expense of biodiversity and climate goals.

BioWanze, a bioethanol production site in Belgium.
BioWanze, a bioethanol production site in Belgium. Bioethanol has long been used in transportation as a means to cut emissions. Critics argue that bioethanol life-cycle emissions and “unforeseen consequences” such as indirect land use change can make the fuel no cleaner than the fossil fuels they seek to replace. Image by Didier Bottin via Flickr (CC BY-NC-SA 2.0).
A farmer walks next to a sugarcane farm in Brazil.
Sugarcane dominates Brazil’s biofuel industry, but its production also has serious environmental drawbacks for the Cerrado savanna biome. Image by Icaro Cooke Vieira/CIFOR via Flickr (CC BY-NC-ND 2.0).

First Generation fuels and debate over their carbon footprint       

To be worthwhile, biofuels must be more ecologically friendly than fossil fuels, while increasing energy supplies and cutting carbon emissions.

Generation One fuels hope to achieve this by utilizing industrial commodity crops like corn, soy, oil palm or sugarcane, which store and release lots of burnable carbon, but which unfortunately also require significant amounts of fossil fuels in their production.

The industry’s hoped-for silver-bullet solution to the agricultural carbon input conundrum remains largely unrealized: Carbon capture and storage (CCS) technology would place the CO2 released by industrial agribusiness practices back underground, but thus far CCS has been plagued by high costs and underperformance.

Then there is the daunting problem of forest loss due to biofuel land use conversion. Some researchers assessing the overall impact of corn ethanol, for instance, found that when direct and indirect land use change was figured in, the carbon-cutting advantages of this biofuel diminished against fossil fuels.

“That’s our main criticism with biofuels: They are simply not helping to reduce emissions,” says Maik Marahrens, senior campaign manager with Transport & Environment, a Europe-based NGO. “Whenever you create demand for crops, there is an expansion of the area where crops are grown.” That means reduced natural carbon storage.

Using industrial agricultural systems to produce vast amounts of biofuels also places pressure on water supplies, while requiring the input of petrochemical fertilizers and toxic pesticides, which can pollute ecosystems.

Corn crop.
Corn has long been used to make ethanol, with governments offering subsidies. But controversy swirls around the climate benefits of corn and other food crops being diverted to biofuel production. Image courtesy of Tyler Lark.

Lark’s biofuels research team found that expanding U.S. biofuel crop production intensified fertilizer use and water supply impacts, and resulted in the carbon intensity of corn ethanol being “no less than gasoline and likely at least 24% higher.”

“[W]hen you consider some of those unintended consequences — the carbon emissions from land use change in particular — it can go a pretty long ways in offsetting some of the benefits of producing corn ethanol,” he said.

Other studies, however, conclude the opposite, finding that corn-based ethanol decreases greenhouse gas emissions, while biodiesel can be cleaner across its life cycle than fossil fuels.

For corn-based ethanol to be a worse emitter than gasoline, there needs to be a “fairly substantial component” of total emissions tied to land use change, particularly indirect change, argues Jem Woods, director of the Centre for Environmental Policy at Imperial College London.

“Those [biofuel] calculations remain extremely controversial, and that’s where the problem sits in terms of getting clarity about the environmental impacts of using biofuels,” Woods says.

“Biofuels remain a complex issue,” agrees Stephanie Searle, director for the fuels program at the International Council on Clean Transportation. “It’s tempting to just say we’re replacing fossil fuels and that’s a good thing … But it’s important to recognize that biofuels carry their own environmental consequences.”

Similar drawbacks apply to First Generation biofuels made from palm oil, an approach that dominates Indonesia’s biofuel sector. Ambitious plans to ramp up palm oil biofuel production and use and eliminate fossil fuels entirely from the country’s transport sector have raised concerns that more forests and wildlife will be lost to meet demand.

Brazil, meanwhile is pursuing still another route. It’s the world’s largest producer of sugarcane, which is being made into a biofuel to serve the country’s fleet of “flex” cars that can run on gasoline or ethanol.

But studies warn that increasing biofuel crop demand in Brazil could come at the expense of the nation’s biomes, including the Cerrado grassland, which has already been greatly impacted by cane production, with further biofuel expansion possibly endangering this already fragmented savanna ecosystem.

Bioenergy CCS is under consideration to drive down carbon emissions related to first-generation biofuel production in Brazil, and to help achieve net-zero goals. But CCS worries David Lapola at Campinas State University in Brazil. “A lot of these new biofuel plantations would take place in Brazil and that’s a problem for us. The concern is whether this would impair food production or even cause deforestation of native habitats.”

Using food crops as a fuel source has long been mired in the food vs. fuel controversy, based on the argument that biofuel production diverts farmlands away from vital food crops, impacting food security and causing hunger, particularly in the developing world.

Biofuels hold the potential to tackle carbon emissions from transportation.
Biofuels hold the potential to tackle carbon emissions from transportation, but their use can involve significant environmental harm. Image by David Sasaki via Flickr (CC BY-NC 2.0).

Second Generation and its potential

Second Generation biofuels are comprised of biomass-based non-food crops such as grasses, and on organic waste streams (ranging from used cooking oils to crop residues such as oil palm waste and coconut husks), and even on human and animal waste.

A host of promising non-food feedstocks remain under investigation. A report by the European Commission, for example, investigated 130 possible candidates as “advanced biofuels.”

The use of waste streams to make biofuel faces a potentially serious problem: Increased demand for limited waste resources, such as used cooking oil, is already threatening a waste material “feedstock crunch” and potential shortage due to ever-increasing demand expected in the coming years, according to an IEA report.

On the other hand, non-food cellulosic crops, have “more and more potential to do something that’s really sustainable,” says John Field, a member of the Bioresource Science and Engineering Group at Oak Ridge National Laboratory in the U.S.

Among some of the most promising Second Generation cellulosic biofuel sources are switchgrass, miscanthus and poplar, say experts. A major benefit of such crops includes their capacity to grow on so-called “marginal lands” or degraded areas — so as not to compete with food crops, or require forest clearing. Researchers also cite accompanying environmental benefits, including improved soil erosion protection and providing greater habitat for wildlife compared to other energy crops.

Switchgrass field.
Perennial crops, including switchgrass, could offer an alternative source of biofuels, say experts. “If you can have a grass that’s on the landscape year-round and use that for bioenergy, you can realize … cool benefits,” says researcher Tyler Lark. “You can make huge strides in reducing nutrient pollution, improving water quality, and keep a lot more carbon in the soil.” Image by Dennis Pennington via Flickr (CC BY-NC 2.0).

Field points optimistically to an assessment of a billion-ton potential in production for cellulosic crops in the U.S. alone. But currently “there’s limited experience with actual on-the-ground deployments of the Second Generation and of more advanced options,” he admits.

Identifying the land where crops could grow is one thing, but maximizing yields and turning waste place crops into viable upscalable fuels, has thus far achieved “a mixed record,” Field says. “There’s definitely a learning curve to be gotten over.”

In a recent study, researchers modeled Second Generation fuel production potential in three Nordic countries. They identified 186,000 hectares (460,000 acres) of abandoned cropland, and 995,000 hectares (2.46 million acres) of cropland threatened by soil erosion — all suitable for bioenergy crop cultivation with switchgrass and willow. However, for this potential to substantially pay off in reduced emissions, the effort would need to be tied closely to technological fixes, including CCS, say researchers.

“We found that if there is no CCS technology available, and with current refinery technology, it is not a given in the Nordic countries that bioenergy will perform better than natural regrowth” for cutting carbon emissions, says lead author Jan Sandstad Næss, a postdoctoral researcher at the Norwegian University of Science and Technology. “So, [success] depends heavily on the technology available and achievable yields locally.”

Past experience with a Second Generation cellulosic non-food crop offers a cautionary tale: Jatropha was a waste place plant touted as a “miracle biofuel crop” more than a decade ago. Its bioenergy potential was praised, with thousands of hectares converted to its production across the globe.

But a range of factors, including low yields, led from boom to bust. Along the way, jatropha production was mired in environmental impacts, including conversion of agricultural lands and deforestation in some countries such as Ghana where it was grown.

According to a 2020 review, “second-generation biofuels have … potential to reduce emissions, provided there is no [land use change].” This report also notes that biofuel land conversions are sometimes coupled with “other impacts, such as acidification, eutrophication, [a large] water footprint and biodiversity loss.”

Placing “some restrictive regulations on bioenergy expansion will be very important to ensure food security, and help prevent loss of natural areas and biodiversity impacts,” says Næss. “It’s a very complicated picture in the end.”

Jatropha seeds.
More than a decade ago, jatropha was hailed as a biofuel miracle crop, but its promise hasn’t come to fruition. Image by Jeff Walker/CIFOR via Flickr (CC BY-NC-ND 2.0).

Third Generation: Algae’s unfulfilled promise

Millions of research dollars have been poured into making algae work as a liquid biofuel. The world’s biggest oil and gas companies dumped cash, and governments funneled scientific expertise and subsidies, into the endeavor. As recently as 2020, a demonstration project conducted by the U.S. Navy boasted algae-derived liquid fuel.

But decades of investment and research have failed to overcome the fundamental challenge of finding a path to cost-effectively upscaling algae-based fuels. This year, even ExxonMobil pulled out of the high-stakes game, joining the likes of Shell, BP and Chevron.

Algae might still have a role to play, said Jason Quinn, an associate professor of mechanical engineering at Colorado State University who has studied algae sustainability for more than a decade. “I think that a huge advantage associated with algae compared to some other traditional terrestrial crops has to do with land use change when it comes to life-cycle emissions.”

Algae environmental obstacles remain numerous and daunting, with concerns raised over water use, fertilizer demand and energy consumption during production. For Woods at Imperial College London, the issues facing algae are “very broad” and come laden with questions. “It’s still really at an early stage of exploitation,” he said, despite all the years of study.

Algae is a potential source of liquid biofuels.
Algae is a potential source of liquid biofuels. But problems with scaling up have thus far made it economically unviable. Image by Oak Ridge National Laboratory via Flickr (CC BY 2.0).

A biofueled future, or not?

Global demand for biofuels is likely to come from First Generation fuels for the next decade or more, say experts, with their deployment accompanied by nagging uncertainties over climate benefits.

“There is the potential for biofuels to play a significant role in decarbonizing the transport sector,” said Searle from the International Council on Clean Transportation. “But … not [via] the path we’ve been going on.

“For the most part we are still reliant on food-based biofuels that may not be giving us any climate savings at all,” she added. “There is also only so much trash, so much sewage, so much available extra land where we could grow these [biofuel] grasses. Even if we managed to get over the cost barriers and technological barriers, it’s impossible for these biofuels to be able to fuel the entire transportation sector.”

Marahrens from Transport & Environment argues for a radical, outside-the-box solution: Instead of continuing the frustrating search for technologically viable, cost-effective, upscalable biofuels, he suggests slashing the need for liquid fuels altogether by electrifying the world’s transportation grids, thereby freeing up existing and proposed biofuel croplands for rewilding and significant carbon storage.

In a recent report, Marahrens’s NGO argued that alternative uses of Europe’s current biofuel-dedicated land could feed millions of people and double carbon savings, while a fraction of that same land could be used to make vast amounts of renewable solar power.

For Lark, the key is learning from past biofuel experiments when looking at where to expand next. “If we’re going to keep [developing] biofuels, we need to do all we can to make sure we’re always working towards something better,” he said. “What we’ve learned as a global community about biofuels is that when we move towards implementation, we do need to think about those potential unintended consequences.”

Banner image: Harvested sugarcane in Karnataka, India. A majority of liquid biofuels are sourced from food crops, such as corn and sugarcane. India, along with Brazil and the U.S., announced ambitious plans earlier this year for a global biofuels expansion. Image by Timor Kodal via Flickr (CC BY-SA 2.0).

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As bioethanol demand rises, biodiversity will fall in Cerrado, study says


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