It is evident that waste generation does not result in positive impacts on climate. Why? Because the manufacture, distribution, and use of products, as well as the management of the resulting waste, they all result in greenhouse gas emissions.
At a global scale, the waste management sector minimally contributes to greenhouse gas [GHG] emissions, approximately the 3-5% of total anthropogenic emissions. However, the sector is in a unique position to move from being a minor source of global emissions to becoming a major saver of emissions. Although minor levels of emissions are released through waste treatment and disposal, the prevention and recovery of wastes avoids emissions in all other sectors of the economy. A holistic approach to waste management would therefore have a positive consequences for GHG emissions from all sectors. A recent report by the US EPA estimates that 42% of total GHG emissions in the US are associated with the management of materials [US EPA 2009].
What are the links between waste and greenhouse gas emissions?
Every waste management practice generates GHG, both directly [emissions from the process itself] and indirectly [through energy consumption].
The disposal of waste produces greenhouse gas emissions in many different ways. First, the anaerobic decomposition of waste in landfills produces methane. Second, the incineration of waste produces carbon dioxide as a by-product. In addition, the transportation of waste to disposal sites produces greenhouse gas emissions from the combustion of the fuel used in the equipment. Finally, the disposal of materials indicates that they are being replaced by new products; this production often requires the use of fossil fuels to obtain raw materials and manufacture the items.
Methane and carbon dioxide are greenhouse gases, whose presence in the atmosphere contribute to climate change. Methane is a particularly potent GHG, and is currently considered to have a global warming potential (GWP) 25 times that of CO2 when a time horizon of 100 years is considered.
The waste sector can save or reduce GHG emissions through several activities:
- Reducing raw material extraction and manufacturing through waste avoidance and material recovery;
- Producing energy that substitutes or replaces energy derived from fossil fuels (i.e. the emissions arising from the use of waste as a source of energy are generally lower than those produced from fossil fuels).
- Storing carbon in landfills (i.e. carbon-rich materials that are largely recalcitrant in anaerobic landfill conditions, such as plastics and wood) and through application of compost to soils.
- Reduce methane emissions from landfills. Waste prevention and recycling (including composting) divert organic wastes from landfills, thereby reducing the methane released when these materials decompose.
- Reduce emissions from energy consumption. Recycling saves energy. Manufacturing goods from recycled materials typically requires less energy than producing goods from virgin materials. Waste prevention is even more effective at saving energy. When people reuse things or when products are made with less material, less energy is needed to extract, transport, and process raw materials and to manufacture products.
- Increase storage of carbon in trees. Trees absorb carbon dioxide from the atmosphere and store it in wood, in a process called “carbon sequestration.” Waste prevention and recycling of paper products allow more trees to remain standing in the forest, where they can continue to remove carbon dioxide from the atmosphere.
In particular, there is general global consensus that the climate benefits of waste avoidance and recycling far outweigh the benefits from any waste treatment technology, even where energy is recovered during the process. Although waste prevention is found at the top of the ‘waste management hierarchy’ it generally receives the least allocation of resources and effort.
Sources of greenhouse gas
Methane emissions from landfill are generally considered to represent the major source of climate impact in the waste sector. Waste such as food, paper, and wood contains organic material. Once waste is deposited in a landfill, microbes begin to consume the carbon in organic material, which causes decomposition. Under the anaerobic conditions prevalent in landfills, the microbial communities contain methane-producing bacteria. As the microbes gradually decompose organic matter over time, methane [approximately 50%], carbon dioxide [approximately 50%], and other gaseous traces [< 1%] are generated and form landfill gas.
Methane from wastewater management is the second largest source of GHG emissions from the waste sector as a whole, according to IPCC [Bogner et al 2008]. Controlled burning, in waste incinerators, also generates CO2 emissions. Where incinerators generate energy, GHG may also be credited. Where incinerators do not generate energy, they will be net energy users, which will also contribute to their total GHG emissions. Aerobic composting processes directly emit varying levels of methane and nitrous oxide, depending on how the process is managed in practice.
UNEP (2011). Waste and Climate Change: Global trends and strategy framework. Osaka, United Nations Environmental Programme. Division of Technology, Industry and Economics.
EPA, U. S. Climate Change and Waste. Reducing Waste can Make a Difference. Washingtong, D.C., United States Environmental Protection Agency.
US EPA 2009, Opportunities to Reduce Greenhouse Gas Emissions through Materials and Land Management Practices, September 2009.
Bogner, J., M. Abdelrafie Ahmed, C. Diaz, A. Faaij, Q. Gao, S. Hashimoto, K. Mareckova, R. Pipatti, T. Zhang, 2008. Waste Management, In Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (eds)], Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Baker, E., E. Bournay, et al. (2004). Vital Waste Graphics. Nairoby, United Nations Environment Programme.