Powering cars with corn and burning wood to make electricity might seem like a way to lessen dependence on fossil fuels and help solve the climate crisis. But although some forms of bioenergy can play a helpful role, dedicating land specifically for generating bioenergy is unwise. It uses land needed for food production and carbon storage, it requires large areas to generate just a small amount of fuel, and it won't typically cut greenhouse gas emissions.
First, dedicating areas to bioenergy production increases competition for land.
Roughly three-quarters of the world's vegetated land is already being used to meet people's need for food and forest products, and that demand is expected to rise by 70% or more by 2050. Much of the rest contains natural ecosystems that keep climate-warming carbon out of the atmosphere, protect freshwater supplies, and preserve biodiversity.
Because land and the plants growing on it are already generating these benefits, diverting land – even degraded, under-utilised areas – to bioenergy means sacrificing much-needed food, timber, and carbon storage.
Second, bioenergy production is an inefficient use of land.
While photosynthesis may do a great job of converting the sun's rays into food, it is an inefficient way to turn solar radiation into non-food energy that people can use. Thus, it takes a lot of land (and water) to yield a small amount of fuel from plants. In a new working paper, World Resources Institute (WRI) calculates that providing just 10% of the world's liquid transportation fuel in the year 2050 would require nearly 30% of all the energy in a year's worth of crops the world produces today.
The push for bioenergy extends beyond transportation fuels to the harvest of trees and other sources of biomass for electricity and heat generation. Some research suggests that bioenergy could meet 20% of the world's total annual energy demand by 2050. Yet doing so would require an amount of plants equal to all the world's current crop harvests, plant residues, timber, and grass consumed by livestock – a true non-starter.
Third, bioenergy that makes dedicated use of land does not generally cut greenhouse gas emissions.
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 directly emits a bit 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 assumption that this release of carbon dioxide is matched and implicitly offset by the carbon dioxide absorbed by the plants growing the biomass.
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 the emissions from burning that biomass. Furthermore, when natural forests are felled to generate bioenergy or to replace the farm fields that were diverted to growing biofuels, greenhouse gas emissions go up.