Biomass (energy)

Biomass energy comes from the recently living (now dead) matter of organisms, used to generate power. Common sources include wood, wood residues, energy crops, agricultural leftovers like straw, and organic waste from homes and factories. Wood and its residues are the most widely used biomass fuel today. This material is considered a renewable energy source and could help fight climate change, but its environmental impact depends heavily on where the biomass comes from and how it’s grown.

Burning wood for energy releases carbon dioxide. This can be largely balanced if new trees are planted in a well-managed forest, since they absorb CO₂ as they grow. However, growing biomass crops can harm biodiversity, degrade soil, and compete with land for food production. It may also require water for irrigation and the use of fertilizers. Globally, there is enough cultivable land and water to produce biomass for both food and energy needs where renewable electricity isn’t cost-effective. Replacing fossil fuels with biomass and renewable electricity for the world’s peak population wouldn’t increase human-caused greenhouse gas emissions. A biomass economy could develop alongside a renewable energy economy.

In energy terms, biomass is matter from recently dead organisms used for bioenergy. Definitions vary—some include only plants, others plants and algae, or plants and animals—but most biomass for energy comes from plants. Bioenergy is a renewable energy type that could help mitigate climate change. The terms biomass and biofuel are sometimes used interchangeably, but it’s now more common to define biofuel as a liquid or gaseous fuel for transportation, making it a subset of biomass. The European Union’s Joint Research Centre defines solid biofuel as raw or processed organic matter of biological origin used for energy, like firewood, wood chips, and wood pellets.

A key drawback of biomass like sawdust is its much lower energy content compared to fossil fuels. Different biomass types serve different purposes. Primary sources for heat or electricity—but not transport—include wood, wood residues, wood pellets, agricultural residues, and organic waste. Biomass processed into transport fuels comes from corn, sugarcane, and soy. Biomass is categorized as either primary (harvested directly for energy) or secondary (residues and waste).

Primary biomass harvested directly for energy includes wood, some food crops, and all perennial energy crops. One-third of the world’s 4 billion hectares of forest is used for wood production or other commercial purposes, and forests supply 85% of all biomass used for energy globally. In the EU, forests provide 60%, with wood residues and waste being the largest source. Woody biomass is often used for traditional cooking and heating in developing countries, providing 25 EJ per year. This practice is highly polluting, and the World Health Organization estimates it causes 3.8 million deaths annually. The United Nations Sustainable Development Goal 7 aims to phase out traditional biomass cooking by 2030. Short-rotation coppices and forests, harvested directly for energy, provide 4 EJ and are considered sustainable. Their potential, along with perennial energy crops, could reach at least 25 EJ annually by 2050. Food crops for energy include sugar-producing crops (like sugarcane), starch-producing crops (like maize), and oil-producing crops (like rapeseed). Sugarcane is perennial; corn and rapeseed are annual. Sugar and starch crops make bioethanol; oil crops make biodiesel. The US is the largest bioethanol producer, and the EU is the largest biodiesel producer. Global production of bioethanol and biodiesel provides 2.2 and 1.5 EJ per year, respectively. Biofuel from food crops is called “first-generation” or “traditional” biofuel and has relatively low emission savings. The IPCC estimates that 0.32 to 1.4 billion hectares of marginal land are suitable for bioenergy worldwide.

Residues and waste are by-products from biological material harvested mainly for non-energy purposes. The most important are wood residues, agricultural residues, and municipal/industrial waste. Wood residues come from forestry operations or wood processing. If not collected for bioenergy, they would decay on the forest floor or in landfills, or be burned at roadside, releasing emissions.