The total decrease in GHG emissions mainly depends on two factors:
1) a reduction in the MSW amount (about 6.2%, passing from 180,448.95 t in 2009 to 169,176.31 in 2011), influenced by the global economic crisis and community awareness of environmental problems (Province of Siena, 2012);
2) optimization and interaction of the waste disposal plants operating in the IWMS.