To put things a bit more into perspective. Assuming the science employed was "good" according to the The Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2002 published by the US EPA in April of 2004 waste activities as a portion of all US GHG emissions represented 3.4% (237.2 Terragrams of Carbon Dioxide Equivalent) in 2002. The term "waste" includes landfills, wastewater treatment, and human sewage. That 3.4% includes methane and nitrogen oxide and relatively insignificant amounts of other GHG. Nitrogen oxide (a hugely more "virulent" GHG than methane) is associated with human sewage while methane is associated with landfills and wastewater treatment.
The EPA estimates that LFG recovery systems have an efficiency of 75%. It also estimates that 49% of all landfill methane was generated at landfills with recovery systems, and the remaining 51% was generated at landfills without LFG recovery. Additionally, of the 49% of all methane generated at landfills with LFG recovery, 49% (or 24% percent of all methane) was generated at landfills that use LFG to generate electricity, and 51% (or 25% of all methane) at landfills that flare LFG (flaring removes the virulency). See EPA 2002. EPA530-R-02-006 - Solid Waste Management and Greenhouse Gases: A Life-Cycle Assessment of Emissions and Sinks.
All in all the contribution of landfilling US style to US GHG emissions would seem to be arguably insignificant relative to the amount of carbon dioxide being pumped skyward from power plants, automobiles, volcanic eruptions, forest fires, etc. even more so when you consider the portion of methane currently being collected in landfill gas operations.
-- Stephan Pollard Environmental Dynamics Doctoral Program University of Arkansas Rm 113 Ozark Hall Fayetteville, AR 72701 Tel: (479) 575-6603 http://www.cast.uark.edu/~sp