is not needed. Benefits The use of biomass in heating systems is beneficial because it uses agricultural, forest, urban and industrial residues and waste to produce heat and/or electricity with less effect on the environment than fossil fuels. This type of energy production has a limited long-term effect on the environment because the carbon in biomass is part of the natural carbon cycle; while the carbon in fossil fuels is not, and permanently adds carbon to the environment when burned for fuel (carbon footprint). Historically, before the use of fossil fuels in significant quantities, biomass in the form of wood fuel provided most of humanity's heating. Because forest based biomass is typically derived from wood that has lower commercial value, forest biomass is typically harvested as a byproduct of other timber harvest operations. Biomass heating provides markets for lower value wood, which enables healthy and profitable forest management. Drawbacks On a large scale, the use of agricultural biomass removes agricultural land from food production, reduces the carbon sequestration capacity of forests that are not managed sustainably, and extracts nutrients from the soil. Combustion of biomass creates air pollutants and adds significant quantities of carbon to the atmosphere that may not be returned to the soil for many decades. The time delay between when biomass is burned and the time when carbon is pulled from the atmosphere as a plant or tree grows to replace it is known as carbon debt. The concept of carbon debt is subject to debate. Actual carbon impacts may be subject to philosophy, scale of harvest, land type, biomass type (grass, maize, new wood, waste wood, algae, for example), soil type, and other factors. Using biomass as a fuel produces air pollution in the form of carbon monoxide, NOx (nitrogen oxides), VOCs (volatile organic compounds), particulates and other pollutants, in some cases at levels above those from traditional fuel sources such as coal or natural gas. Black carbon – a pollutant created by incomplete combustion of fossil fuels, biofuels, and biomass – is possibly the second largest contributor to global warming. In 2009 a Swedish study of the giant brown haze that periodically covers large areas in South Asia determined that it had been principally produced by biomass burning, and to a lesser extent by fossil-fuel burning. Researchers measured a significant concentration of 14C, which is associated with recent plant life rather than with fossil fuels.