What is the role of bioenergy in a sustainable food future? The answer must recognize the intense global competition for land, and that any dedicated use of land for bioenergy inherently comes at the cost of not using that land for food, feed, or sustained carbon storage.

The world needs to close a 70 percent gap between the crop calories that were available in 2006 and the calorie needs anticipated in 2050. During the same period, demand for meat and dairy is projected to grow by more than 80 percent, and demand for commercial timber and pulp is likely to increase by roughly the same percentage. Yet three-quarters of the world’s land area capable of supporting vegetation is already managed or harvested to meet human food and fiber needs. Much of the rest contains the world’s remaining natural ecosystems, which need to be conserved and restored to store carbon and combat climate change, to protect freshwater resources, and to preserve the planet’s biological diversity.

A growing quest for bioenergy exacerbates this competition for land. In the past decade, governments have pushed to increase the use of bioenergy—the use of recently living plants for energy—by using crops for transportation biofuels and increasingly by harvesting trees for power generation. Although increasing energy supplies has provided one motivation, the belief that bioenergy use will help combat climate change has been another. However, bioenergy that entails the dedicated use of land to grow the energy feedstock will undercut efforts to combat climate change and to achieve a sustainable food future.

What are the implications of crop-based biofuels for the supply of food?

Bioenergy challenges a sustainable food future most directly when government policy causes diversion of food crops into ethanol or biodiesel for transportation. Biofuels from food crops today—such as maize, vegetable oils, and sugarcane—provide about 2.5 percent of the world’s transportation fuel. Crop needs for 2050 projected by the Food and Agriculture Organization of the United Nations (FAO) assume that this penetration rate will remain roughly the same. Yet even this small share of transportation fuel in 2050 would have substantial implications for the crop calorie gap. If crop-based biofuels were phased out, the 2050 crop calorie gap would decrease from 70 percent to about 60 percent, a significant step toward a sustainable food future.

But the FAO biofuel projection for 2050 is modest. Some of the largest fossil-fuel consuming regions, such as the United States and Europe, have established higher biofuel targets that amount to at least 10 percent of transportation fuel by 2020. If such targets were to go global by 2050, meeting them would consume crops with an energy content equivalent to roughly 30 percent of the energy in today’s global crop production. Consequently, the crop calorie gap would increase from 70 percent to about 90 percent, making a sustainable food future even more difficult to achieve.

Overall, phasing out the use of crop-based biofuels instead of meeting an expanded 10 percent target is likely to mean the difference between a 90 percent crop calorie gap and a 60 percent gap. It is therefore a potent strategy for sustainably meeting future food needs.

Would cellulosic biofuels avoid this competition for food?

Cellulosic biofuels (sometimes referred to as “second generation”) may use crop residues or other wastes, but most plans for these biofuels rely on planting and harvesting fast-growing trees or grasses. At least some direct competition with food is still likely because such trees and grasses grow best and are most easily harvested on relatively flat, fertile lands—the type of land already dedicated to crops.

Using cropland to grow trees and grasses rather than food crops for biofuels will probably not reduce, let alone eliminate, competition for cropland. Trees and grasses will have a hard time producing more biofuels per hectare than today’s crop-based biofuels. For example, a hectare of maize in the United States currently produces roughly 1,600 gallons of ethanol (about 6,000 liters). For cellulosic ethanol production just to match this output, the grasses or trees must achieve almost double the national cellulosic yields estimated by the U.S. Environmental Protection Agency and two to four times the perennial grass yields farmers actually achieve today in the United States.

Alternatively, cellulosic biofuels might rely on harvesting existing forests or producing fast-growing trees or grasses on the world’s grasslands or woody savannas. But harvesting standing forests reduces their carbon storage and typically their ability to support biodiversity. Burning the trees for energy results in net carbon dioxide emissions for decades until the trees regrow. Likewise, converting woody savannas to bioenergy sacrifices the ecosystem’s abundant carbon storage and biodiversity, while converting pasturelands sacrifices their ability to provide food from livestock.

What about using “degraded” land for bioenergy?

Some researchers argue that growing bioenergy feedstocks on degraded lands would avoid competition for land. The term “degraded lands” has many meanings, but no matter how it is defined, it is hard to find lands that are doing little today for people, climate, or biodiversity and that could produce bioenergy crops abundantly. There are a few possible candidates, such as cleared forests of Indonesia that are overrun by alang-alang grasses. But while some of these lands could support bioenergy plants, the opportunity costs of doing so are high in a world that needs at least 70 percent more crops, livestock, and commercial timber by 2050. Indonesia’s alang-alang grasslands, for example, provide a low-opportunity-cost way of meeting rapidly growing demand for palm oil for food. Using these grasslands instead for biofuels could push growers to convert forests to meet food product demands for palm oil.

Some researchers also point to abandoned farmland as a candidate for bioenergy production that avoids competition for land. But abandoned farmlands typically regenerate into forests, woodlands, or grasslands if left alone, which provide climate benefits that are already assumed and counted in climate change assessments. These benefits would be sacrificed by using that land for bioenergy.

By adding irrigation water, some degraded or dry lands might produce biofuels while avoiding this competition with food and carbon storage. Examples might include recirculating water systems or saline ponds that grow algae in the desert. Although this kind of production might eventually be necessary to supply biofuels for applications such as aviation, it is likely to be expensive and should only be employed at scale to reduce greenhouse gas emissions after more cost-effective strategies are fully utilized.

Can increased crop and pasture yields supply bioenergy as part of a sustainable food future?

Crop and pasture yields can increase. Yet to avoid clearing natural ecosystems while still meeting projected food crop and livestock demands, crops and pasture yields overall will have to grow even faster over the coming four decades than they did over the previous four decades. Any yield improvement potential is therefore already needed to meet growing food demands.

What are the implications of wider bioenergy targets?

The push for bioenergy is extending beyond transportation biofuels to the harvest of trees and other sources of biomass for electricity and heat generation. Some organizations have advocated for a bioenergy target of meeting 20 percent of the world’s total energy demand by the year 2050, which would require around 225 exajoules of energy in biomass per year. That amount, however, is roughly equivalent to the total amount of biomass people harvest today—all the crops, plant residues, and trees harvested by people for food, timber, and other uses, plus all the grass consumed by livestock around the world.

The world will still need food for people, fodder for livestock, residues for replenishing agricultural soils, wood pulp for paper, and timber for construction and other purposes. To meet these needs at today’s level while at the same time meeting a 20 percent bioenergy target in 2050, humanity would need to at least double the world’s annual harvest of plant material in all its forms. Those increases would have to come on top of the already large increases needed to meet growing food and timber needs. Even assuming large increases in efficiency, the quest for bioenergy at a meaningful scale is both unrealistic and unsustainable.

Why does a small share of energy require such vast amounts of biomass?

Although photosynthesis is an effective means of producing food, wood products, and carbon stored in vegetation, it is an inefficient means of converting the energy in the sun’s rays into a form of non-food energy useable by people. Fast-growing sugarcane on highly fertile land in Brazil, for example, converts only around 0.5 percent of incoming solar radiation into sugar, and only around 0.2 percent ultimately into ethanol. For maize grown in Iowa, the energy conversion rate is around 0.3 percent into biomass and 0.15 percent into ethanol. Even assuming highly optimistic estimates of future yields and conversion efficiencies, fast-growing grasses on productive U.S. farmland would only do slightly better, converting around 0.7 percent of sunlight into biomass and around 0.35 percent into ethanol. Such low conversion efficiencies explain why it takes a large amount of productive land to yield a small amount of bioenergy, and why bioenergy can so greatly increase the global competition for land.

How does bioenergy compare to alternative uses of land to produce energy?

Like bioenergy, solar photovoltaics (PV) convert sunlight directly into energy that is useable by people, but PV’s solar conversion efficiency—and therefore its land-use efficiency—is much higher. On most of the world’s land, PV systems today can generate more than 100 times the useable energy per hectare than bioenergy is likely to produce in the future even using optimistic assumptions. In addition, because electric motors can be 2–3 times more efficient than internal combustion engines, PV can result in 200–300 times more useable energy for vehicle transport than bioenergy per hectare (although fully realizing this potential will require battery production to become more energy efficient). PV can also utilize areas that do not naturally support much (if any) vegetation, such as deserts, dry lands, and rooftops. Overall, PV can contribute to energy security and climate goals with a fraction of the competition for the world’s productive land.

Use of bioenergy at a globally meaningful level will push up costs of food, timber, and land, while solar energy costs are likely to become cheaper over time. Although solar power eventually may face storage limitations, promising storage technologies are already emerging, and solar energy could increase multifold to meet more than 20 percent of global energy demand before running into serious storage constraints.

Is bioenergy nevertheless good for climate?

Burning biomass, whether directly as wood or in the form of ethanol or biodiesel, emits carbon dioxide, just like burning fossil fuels. In fact, burning biomass emits at least a little more carbon dioxide than fossil fuels for the same amount of generated energy. But most calculations claiming that bioenergy reduces greenhouse gas emissions relative to burning fossil fuels do not include the carbon dioxide released when biomass is burned. They exclude it based on the theory that this release of carbon dioxide is matched and implicitly “offset” by the carbon dioxide absorbed by the plants growing the biomass feedstock. Yet if those plants were going to grow anyway, simply diverting them to bioenergy does not remove any additional carbon from the atmosphere and therefore does not offset emissions from burning that biomass.

For example, in a world without biofuels, farmers grow maize for food and feed (absorbing carbon dioxide) while automobiles run on gasoline (emitting carbon dioxide). When ethanol diverts the already-growing maize to biofuels to run the automobiles, those maize fields do not absorb any additional carbon, and the automobiles still emit roughly the same quantity of carbon dioxide. Maize growth by itself does not reduce greenhouse gas emissions because the carbon dioxide absorption would occur anyway.

Ultimately, plant growth can offset greenhouse gas emissions only to the extent that bioenergy leads to more plant growth than would occur anyway, directly or indirectly. That happens only to a limited extent (see “additional biomass” below) and cannot happen at a meaningful scale because the world’s productive land and potential to boost crop, pasture, and timber yields is already needed to meet rising demands for food and timber. Analyses generally attribute greenhouse gas emissions reductions to bioenergy by counting the benefits of plant growth that would occur anyway—thus “double counting” this plant growth.

What accounts for large estimates of bioenergy potential?

Large estimates of bioenergy potential double count biomass, leading to a double counting of carbon. Most of the world’s land grows plants each year. Some of these plants are consumed for food, fiber, and timber while others are replenishing or increasing carbon in soils and vegetation. The latter keeps land productive and combats climate change. Like a monthly paycheck, plant growth will occur again once we use it. But because people use this annual growth—just as they use their monthly paycheck—people cannot divert plant growth to some other use except at the expense of what they are already doing with it. To provide bioenergy except at the cost of food, timber, or carbon storage, people must generate additional biomass, which means biomass that is not already growing or being used.

But instead of counting only additional biomass, estimates suggesting that the world has a large potential to produce bioenergy double count biomass and land by assuming incorrectly that bioenergy can freely divert biomass or land that is already in use. For example, the build-up of wood and carbon that is already occurring in some forests is helping to reduce the rate of climate change. If this increasing biomass is harvested for energy, these climate benefits would be lost. Other examples of double counting include counting woody savannas that would lose much of their abundant carbon storage if converted to produce bioenergy, and counting grasslands whose use for bioenergy would sacrifice livestock production.

What types of biomass are additional? There are some sources of additional biomass that are consistent with a sustainable food future and will therefore reduce greenhouse gas emissions because they do not compete with food production or otherwise make dedicated use of land. This category includes some level of forest and agriculture residues left behind after harvest (some need to remain on the ground to maintain soil fertility); timber processing wastes including sawdust and “black liquor;” and any unused manure, urban wood waste, municipal organic waste, and landfill methane. Another category is biomass grown in excess of what would have grown absent the demand for bioenergy, such as growing winter cover crops for energy and replacing traditional—yet inefficient—fuel wood harvests in some poor countries with wood grown in agroforestry systems and local plantations. Using second generation technologies to convert crop residues into bioenergy has potential and avoids competition for land. But a challenge will be to do this at scale, since most of these residues are already used for animal feed or are needed for soil fertility, and others are expensive to harvest.

Although one or more of these sources may be important in certain local contexts, studies indicate that their potential to meet a sizeable share of energy needs is limited. These feedstocks should therefore be prioritized to energy uses that can probably not be met any other way, such as low-carbon fuels for airplanes.

What should policymakers do?

In light of these findings, phasing out bioenergy that uses crops or that otherwise makes dedicated use of land is a sound step toward a sustainable food future. Doing so will require five policy changes:

Governments should fix flaws in the accounting of the carbon dioxide consequences of bioenergy in climate treaties and in many national- and state-level laws.

Governments should phase out the varied subsidies and regulatory requirements for transportation biofuels made from crops or from sources that make dedicated use of land.

Governments should make ineligible from low-carbon fuel standards biofuels made from crops or from the dedicated use of land.

Governments should exclude bioenergy feedstocks that rely on the dedicated use of land from laws designed to encourage or require renewable energy.

Governments should maintain current limits on the share of ethanol in gasoline blends.

By concurrently pursuing policies that encourage solar energy development, policymakers can catalyze far more energy growth in a manner fully compatible with a sustainable food future.