HOw does the temporal effect of long-term landfill emissions affect global warming impacts assessment?
HOw does the temporal effect of long-term landfill emissions affect global warming impacts assessment?
Embedded Files
Landfills are a major contributor of anthropogenic CH4 emissions. Since the greenhouse gas (GHG) emissions associated with landfilling waste can occur over decades to centuries, the standard static approach to estimating global warming impacts may not accurately represent the global warming impacts of landfills. The objective of this study is to assess the implications of using 100 yr and 20 yr static and dynamic global warming potential (GWP) approaches to estimate the global warming impacts from municipal solid waste landfills.
A life-cycle model was developed to estimate GHG emissions for three gas treatment cases (passive venting, flare, CH4 conversion to electricity) and four decay rates. We considered the disposal of 1 metric ton of wet mixed municipal solid waste (MSW) into a U.S. landfill with an average size (accepting 200,000 metric tons of MSW annually and operating over 50 years). We calculated GHG emissions over 1,000 years, covering 99.99% of total potential emissions from landfill assuming a minimum bulk decay rate of 0.02 yr-1.
When using a 100-yr GWP for a decay rate of at least 0.04 yr-1, the dynamic GWP estimates are within the range of the AR4 and AR5 static values. This indicates that AR4 and AR5 static values may be used to provide reasonable lower and upper bounds on the 100-yr global warming impact from many landfills. However, at a decay rate of 0.02 yr-1, the dynamic 100-yr GWP is significantly lower than the static AR4 value because 13–39% of the CH4 emissions occur after year 100. For the 100 yr GWP, other model uncertainties (e.g., static GWP values, decay rate, moisture content, or gas collection efficiency) generally had a larger effect on the estimated global warming impact than the choice of static versus dynamic GWP methods.
When using a 20-yr time horizon, dynamic GWP estimates are 9 to 84% lower than the static AR4 values because 66 to 83% of the CH4 emissions occur after year 20. The dynamic method attempts to account for only the warming that occurs during the time horizon but does not consider the majority of the GHG emissions occurring after the selected time horizon. Thus, the temporal effect is a potentially dominant source of uncertainty, particularly when using relatively short time horizons and small decay rates.
These findings show that when comparing single-point GWP values, the choice of static versus dynamic is relatively unimportant for most landfills. While dynamic GWPs consider temporal variance and provide useful estimates for the warming over a set time horizon, for most comparative analyses, static values provide reasonable bounds for the actual 100 yr warming impact. However, for landfills with a decay rate of ≤0.02 yr-1 and short time horizons, the temporal variance becomes important in the relative rankings of landfills compared to other MSWM alternatives with more immediate emissions profiles (e.g., waste-to-energy).
Page updated
Google Sites
Report abuse