Published by Australian Academy of Science
Biomass – the growing energy resource Box 1 | Biomass and greenhouse

The burning of fossil fuels such as coal, oil and natural gas has increased the concentration of carbon dioxide, methane and other gases in the atmosphere. Most scientists say that this will lead to a general warming of the world's climate, a phenomenon known as the enhanced greenhouse effect or, more simply, the greenhouse effect. The concern of scientists has sparked renewed interest in energy supplies that don't emit greenhouse gases into the atmosphere.

Energy from biomass is one such alternative. This source is usually considered to be greenhouse-neutral, which means it neither adds to nor reduces greenhouse gases. This is because, theoretically at least, all the carbon dioxide that was removed from the atmosphere by the growing plants is later released when biomass fuel is burnt.

But there are scenarios in which biomass could be greenhouse-positive. Biomass could contribute to the greenhouse effect if, for example, forests were harvested and used but not replaced. Burning biomass would have the net effect of adding greenhouse gases to the atmosphere, because the carbon formerly stored in the biomass would be released as carbon dioxide

On the other hand, biomass could be greenhouse-negative and help reduce greenhouse gases in two ways. First, by substituting a renewable resource for fossil fuels – for example, using ethanol produced from biomass, instead of petroleum – we could achieve a net reduction in greenhouse gas emissions. Second, if biomass is left to rot – as in a landfill site – it produces methane, which traps heat more efficiently than carbon dioxide and is therefore a more potent greenhouse gas. By capturing the methane and using it for energy we produce carbon dioxide, thereby reducing (but not eliminating) the impact on the enhanced greenhouse effect.

Related sites

• Greenhouse gases (Nova: Science in the news, Australian Academy of Science)

• Global warming and the Third World: Biomass as an energy source (Tiempo Climate Cyberlibrary, UK)

Other boxes

Box 2. Introduction to food chains

Box 3. Ways of extracting biomass energy