The Impact of Municipal Solid Waste on Greenhouse Gas Emissions
Excerpts from the 2002 EPA report Solid Waste Management and Greenhouse Gases: A Life-Cycle Assessment of Emissions and Sinks
[EPA] focused on those aspects of [a product’s] life cycle that have the potential to emit GHGs [greenhouse gases] as materials change from their raw states to products and then to waste. Exhibit ES-2 shows the steps in the life cycle at which GHGs are emitted, carbon sequestration is affected, and utility energy is displaced. As shown, [EPA] examined the potential for these effects at the following points in a product’s life cycle:
- Raw material acquisition (fossil fuel energy and other emissions, and changes in forest carbon sequestration);
- Manufacturing (fossil fuel energy emissions); and
- Waste management (CO2 emissions associated with composting, non-biogenic CO2 and nitrous oxide (N2O) emissions from combustion, and CH4 emissions from landfills); these emissions are offset to some degree by carbon storage in soil and landfills, as well as avoided utility emissions from energy recovery at combustors and landfills.
At each of these points [in a product’s life cycle], [EPA] also considered transportation-related energy emissions. Estimates of GHG emissions associated with electricity used in the raw materials acquisition and manufacturing steps are based on the nation’s current [2002] mix of energy sources, including fossil fuels, hydropower, and nuclear power.
Exhibit ES-3 shows how GHG sources and sinks are affected by each waste management strategy. For example, the top row of the exhibit shows that source reduction (1) reduces GHG or emissions from raw materials acquisition and manufacturing; (2) results in an increase in forest carbon sequestration; and (3) does not result in GHG emissions from waste management. The sum of emissions (and sinks) across all steps in the life cycle represents net emissions.
Exhibit ES-2: Greenhouse Gas Sources and Sinks Associated with the Material Life Cycle
Exhibit ES-3: Components of Net Emissions for Various MSW Management Strategies
Municipal Solid Waste (MSW) Management Strategy |
GHG Sources and Sinks |
||
|
Raw Materials Acquisition and Manufacturing |
Changes in Forest or Soil Carbon Storage |
Waste Management |
|
|
Source Reduction |
Decrease in GHG emissions, relative to the baseline of manufacturing |
Increase in forest carbon sequestration (for organic materials) |
No emissions/sinks |
|
Recycling |
Decrease in GHG emissions due to lower energy requirements (compared to manufacture from virgin inputs) and avoided process non-energy GHGs |
Increase in forest carbon sequestration (for organic materials) |
Process and transportation emissions associated with recycling are counted in the manufacturing stage. |
|
Composting (food discards, yard trimmings) |
No emissions/sinks |
Increase in soil carbon storage |
Compost machinery emissions and transportation emissions |
|
Combustion |
No change |
No change |
Non-biogenic CO2, N20 emissions, avoided utility emissions, and transportation emissions |
|
Landfilling |
No change |
No change |
CH4 emissions, long-term carbon storage, avoided utility emissions, and transportation emissions |