Biomass is a US-EPA stated CO2 reduction technology, improves forest health, greatly reduces forest fire risk and reduces landfill waste.
Renewable energy sources such as Wind, Solar, Hydro, etc are considered Zero Carbon as they do not directly generate CO2 or other GHGs as a byproduct of producing electricity. Fossil fuels such as Coal and Natural Gas however, release GHGs (amongst other pollutants) into the atmosphere. Forest waste-based Biomass also generates GHGs and on a simple static comparison, can release more GHGs / KWh produced than the normally larger and thus more efficient coal and natural gas power plants.
However, the key difference with wood-based biomass power is that it does not actually produce new carbon. It simply releases the carbon that was absorbed by the tree over its normal 30-40 year harvest cycle. The distinction between using biomass fuel rather than coal or gas is that the carbon discharged when biomass is burned was already part of nature because of the plant from which it was derived. When coal or gas is used for power generation, the CO2 released into the environment was from millions of years ago and from underground, and hence is releasing additional new carbon into the atmosphere.
The US biomass power industry uses 100% wood waste from sustainably-managed forestry operations. Trees removed in logging operations must be replanted and forestry operations are managed such that their operations are sustainable. Thus the carbon released by burning wood waste from US forestry operations is in effect carbon-neutral over a 30-40 year forest harvesting cycle. As forests grow, carbon dioxide (CO2) is removed from the atmosphere via photosynthesis. The CO2 absorbed is converted into organic carbon, stored in woody biomass, and oxygen is returned to the atmosphere. Trees release their stored carbon as CO2 when they die, decay or are combusted, completing the carbon cycle. Carbon in biomass returns to the atmosphere regardless of whether it is burned for energy, allowed to biodegrade naturally or lost in a forest fire. The forest products industry facilitates the flow of CO2 in and out of forests through both biomass combustion and long-term carbon sequestration in products. Overall, the flow of forest CO2 is carbon positive when forests are sustainably managed, and the forest-to-products system remains a net sink of CO2 from the atmosphere.
The life cycle of a forest is typically 35-40 years from the date on which a 40 acre block is cleared and replanted by the land owner. These 40 acre sections are prepared and planted with expected thinnings at 8 and 15 years and additional logging every 5 years or so thereafter until a final clearing again at 40 years. This cycle is codified into sustainable harvest practices by several organizations (SFC, FSC & PETC, SBP). All forest land managers abide by this practice and depend on regional biomass power plants to buy the significant volumes of residuals (tops & limbs) that result from these continuous forest activities. While forest growth (measured in tons/acre/year) varies from Alaska to Georgia as a direct correlation to climatic conditions, the tonnage removed annually in a 50-mile radius is a known amount and professionally managed forestlands are independently audited in order to certify that all removals of trees (by tonnage) never exceeds the average annual growth.
Under these conditions, it is accurate to state that carbon released by burning wood waste from US forestry operations is, in fact, carbon-neutral over the 30-40 year forest harvesting cycle.
The greenhouse gas benefits of energy from biomass harvested from sustainably managed forests has been recognized repeatedly by an abundance of studies, agencies, institutions, legislation and rules around the world, including guidance from the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC) and the reporting protocols of the UN Framework Convention on Climate Change.
The US EPA has recently gone on record to state that biomass-derived power generation is a carbon reduction technology.
In addition, the EPA states "We anticipate that states likely will consider biomass-derived fuels in energy production as a way to mitigate the CO2 emissions attributed to the energy sector and include them as part of their plans to meet the emission reduction requirements..."
Biomass plants have no impact on deforestation as they were designed to burn waste wood/residual fiber sourced from nearby sawmills and pulp mills as well as from ongoing forest thinning operations. Normally they are buying feedstock from companies that produce finished lumber or paper goods in addition to providing a critical service to forest health by reducing materials left behind from logging operations. Other than thinnings, pine beetle kill or fire hazard management, whole trees are not specifically harvested to power biomass plants.
An increasingly important benefit of biomass power is to reduce fire risks by removing residuals from forest harvests as well as whole trees that have died from disease, drought and other natural causes. Many states are facing an increasing forest fire threat and a lengthening of the forest fire season due to climate change and drought. California is particularly hard hit, where almost 50% of the US biomass plants are located. By providing a safe, continuous means by which to dispose of waste forest residuals (typically 20-25% of each tree harvested for a sawmill or a pulp mill is left behind), the biomass generation industry delivers an immediate reduction in wildfire risk plus improvements in overall forest health.
The New York Times recently highlighted this problem.
Disposing of biomass in valuable municipal landfills is a very short-sighted and costly use of dwindling landfills throughout the US. In many regions of the country, it is no longer legal to landfill biomass waste. Many municipalities require that garden and biomass materials be delivered to separate processing facilities to convert the material into compost. Most of these operations charge a fee-per-ton to receive the material.
Open burning is still common in many parts of the US and Canada. In the more arid regions, however, such means of disposal has long been banned, and hence biomass power plants are one of a limited number of solutions for disposal.