Source: IEA BioenergyTask 38 [author Robert Matthews]

Biomass is essentially stored solar energy - the sun’s energy is used by plants during photosynthesis to convert atmospheric CO2 to carbon and oxygen.
Unlike fossil fuel, which when released to the air causes high atmospheric concentrations of CO2, biomass takes carbon out of the atmosphere. When the biomass is produced from repetitively and continuously regenerating plantations, it is a sustainable closed carbon cycle with generates electricity without affecting the atmosphere with carbon dioxide levels, as the CO2 produced during biomass combustion is re-absorbed during each cycle of biomass production.
This is especially effective with SRC (short-rotation-coppice) biomass which is grown on land which is not suitable for food production.

Sustainably produced woody biomass is ideal for renewable base load power, as base loads power from biomass results in a corresponding reductions in base load power generated using coal.