Taking methane’s strength into account, [conservatively using the 100-yr methane global warming potential of 28,] landfills emit more greenhouse gases as CO₂ equivalents, but that’s just part of the story.
For a more accurate comparison, a lifecycle analysis allows us to take into account a few more factors. Lifecycle analysis looks at the environmental effects of all stages of a product or service.
This analysis allows a direct comparison between the climate impacts of landfills and waste-to-energy.
Both landfills and waste-to-energy facilities emit CO₂ from biogenic materials. The carbon in these emissions is part of the normal carbon cycle. Composting and anaerobic digestion also release CO₂ from biogenic material.
Historically, biogenic CO₂ emitted when biogenic materials decompose or are combusted was considered “carbon neutral” meaning it was assumed to have no impact on the climate system. We now know this is not always the case. However, waste sources of biogenic carbon are widely recognized by the scientific community as being very close to carbon neutral.
Waste-to-energy facilities do emit fossil-based CO₂, which is included in greenhouse gas comparisons.
Some landfills and all waste-to-energy facilities recover energy from the waste received. In most cases, this energy takes the form of electricity exported to the power grid.
This electricity avoids the need to burn fossil fuels to generate electricity, saving greenhouse gas emissions.
Waste-to-energy facilities reduce more greenhouse gases than landfills because they generate much more electricity from a ton of waste.
Waste contains metal, even in communities with really good recycling programs.
Waste-to-Energy facilities also recover ferrous and non-ferrous metals that would otherwise be lost forever in a landfill. Landfills don't recycle any metals.
Recycling these metals helps reduce greenhouse gas emissions that would have occurred if new metals were manufactured from raw materials.