Biofuels create several serious problems, ranging from rising food prices to water pollution to a surprisingly poor energy payoff. While they’re marketed as a cleaner alternative to fossil fuels, the full picture is more complicated. Some biofuels may actually warm the planet more than the gasoline they replace, and their production strains farmland, water supplies, and ecosystems in ways that undermine their environmental promise.
Food Prices Rise When Crops Become Fuel
The most immediate problem with biofuels is that they compete directly with food. Corn, soybeans, sugarcane, and rapeseed are all used to make ethanol or biodiesel, which means a significant share of global cropland is growing fuel instead of feeding people. A Federal Reserve analysis found that the increase in worldwide biofuels production pushed up corn prices by 27%, soybean prices by 21%, and sugar prices by 12% in the two years leading up to June 2008, a period that coincided with a global food crisis. Overall, biofuel production accounted for just over 12% of the rise in the international food price index during that time.
This isn’t a one-time event. As long as biofuel mandates require blending ethanol into gasoline, demand for corn and other feedstocks stays elevated, keeping upward pressure on food prices. The people hit hardest are in developing countries, where families spend a larger share of their income on staple grains.
The Carbon Math Often Doesn’t Add Up
Biofuels are supposed to reduce greenhouse gas emissions, but the calculation changes dramatically once you account for what happens to the land. When forests or grasslands are cleared to grow biofuel crops, the carbon stored in that vegetation and soil gets released into the atmosphere. This creates a “carbon debt” that takes decades or even centuries to repay through the modest emissions savings of burning biofuel instead of gasoline.
A study published in the Proceedings of the National Academy of Sciences examined this effect in Brazil, where sugarcane ethanol and soybean biodiesel drive significant deforestation. The researchers estimated that indirect land clearing for these crops would create a carbon debt taking roughly 44 years to repay for sugarcane ethanol and 246 years for soybean biodiesel. If crop yields don’t improve, soybean biodiesel’s payback period stretches past 300 years. In other words, biofuels produced on converted land can make climate change worse for generations before they start helping.
Fertilizer Emissions Can Cancel Out Climate Benefits
Even setting land conversion aside, growing biofuel crops requires heavy nitrogen fertilizer use, and that fertilizer releases nitrous oxide, a greenhouse gas roughly 265 times more potent than carbon dioxide. Research published in Philosophical Transactions of the Royal Society B found that for corn ethanol and rapeseed biodiesel, the warming caused by nitrous oxide emissions from fertilizer can match or even exceed the cooling effect of replacing fossil fuels. The emission factor the researchers used (3 to 5% of applied nitrogen converting to nitrous oxide) means that for certain crops, the biofuel is a net negative for the climate before it ever reaches a gas tank.
Sugarcane ethanol performs somewhat better on this metric because sugarcane uses nitrogen more efficiently, but corn and rapeseed, two of the most common biofuel feedstocks in the US and Europe, fall squarely into the problem zone.
Water Pollution and Dead Zones
The US Renewable Fuel Standard, which mandates corn ethanol blending, has measurably worsened water quality across agricultural regions. A 2022 analysis in PNAS found that the policy increased synthetic nitrogen fertilizer application by 7.5% and boosted nitrate leaching from farmland by 5.3%. Phosphorus runoff increased by 3.2%, driven by more fertilizer use and a 4.7% rise in soil erosion.
These nutrients flow into rivers and eventually into places like the Gulf of Mexico, where they fuel massive algal blooms. When the algae die and decompose, they consume oxygen in the water, creating “dead zones” where fish and other marine life can’t survive. The Gulf of Mexico dead zone, which can stretch to the size of New Jersey in bad years, is fed largely by agricultural runoff from the Corn Belt. Biofuel production adds meaningfully to that problem.
Enormous Water Consumption
Growing corn for ethanol is extraordinarily water-intensive. Producing a single gallon of corn ethanol requires between 10 and 324 gallons of water, depending on how much irrigation the crop needs. Compare that to gasoline, which requires 3.4 to 6.6 gallons of water per gallon of fuel. Even at the low end, corn ethanol uses roughly twice as much water as gasoline. In heavily irrigated regions, it can use 50 times more.
Switchgrass, a proposed alternative feedstock, performs better at 1.9 to 9.8 gallons of water per gallon of fuel, but switchgrass-based cellulosic ethanol has never scaled to commercial viability. The vast majority of ethanol produced today comes from corn, and that production competes with drinking water, livestock, and other crops for increasingly strained water supplies.
Biodiversity Loss From Expanding Cropland
Biofuel demand pushes agriculture into natural habitats. A study in Global Change Biology: Bioenergy quantified species loss from first-generation biofuel production and found that habitat destruction was the dominant driver, with Brazilian soybean, Brazilian sugarcane, and Chinese corn having particularly large biodiversity impacts. Oil palm plantations, which supply biodiesel in Southeast Asia, are especially destructive. Comparisons between natural tropical forests and palm plantations show dramatic drops in species richness across birds, mammals, and insects.
The variation within countries is striking. Depending on location, biodiversity impacts can differ by a factor of 9 to 22, meaning a biofuel crop grown in one region may be vastly more damaging than the same crop grown elsewhere. This makes blanket biofuel policies especially problematic, since they don’t account for where the crops actually end up being planted.
Poor Energy Return
One of the less intuitive problems with biofuels is how little energy you get back for the energy you put in. Corn ethanol in the US has an energy return on investment (EROI) between 0.69:1 and 1.5:1. At the low end of that range, you’re spending more energy growing, harvesting, fermenting, and distilling the corn than you get from burning the ethanol. Even at the high end, you barely break even. For comparison, energy analysts consider anything below 3:1 a net energy sink for society, and global-average oil products deliver above 8:1.
This means that corn ethanol depends heavily on fossil fuel inputs (diesel for tractors, natural gas for processing plants, petroleum-based fertilizers) to exist at all. It’s less an alternative to fossil fuels and more a way of laundering fossil energy through a cornfield at significant cost.
Engine Damage and Storage Problems
Ethanol is corrosive to certain metals and materials found in engines and fuel systems. Copper and carbon steel are particularly vulnerable. Copper appears in electrical contacts inside fuel pumps, and corrosion there can cause the pump to malfunction. Carbon steel is used in gas tanks, where corrosion can lead to fuel leaks. Rubber seals and polymeric components also degrade with prolonged ethanol exposure, especially at higher blend levels like E30 or E85.
Biodiesel has its own storage challenges. Pure biodiesel (B100) can go out of specification for oxidation stability within four months, even when it starts with relatively good stability. As it degrades, it forms acids and insoluble deposits that can clog fuel filters and injectors. Synthetic antioxidants help, but they add cost and complexity to a fuel that’s already more expensive to produce than petroleum diesel. For anyone storing biodiesel for backup generators or seasonal equipment, shelf life is a real practical concern.