SOURCE: EOS and Journal of Geophysical Research

DATE: November 13, 2018

SNIP: As cities around the world continue to swell, urban dwellers account for a larger and larger share of the world’s greenhouse gas emissions. In fact, the 2014 Intergovernmental Panel on Climate Change report attributes more than 70% of anthropogenic emissions to cities. To mitigate climate change, scientists and policy makers believe it is crucial to establish reliable estimates of urban emissions and their sources.

Recent research suggests that state and national greenhouse gas inventories poorly characterize urban emissions—particularly for methane, which carries more global warming potency than carbon dioxide on a per mass basis over a 20-year horizon.

Now Ren et al. suggest these inventory estimates may actually be lower than observed values, by a factor of nearly 3 in some metropolitan areas.

The results indicate that landfills play a more significant role in methane emissions than previously believed: The total methane emitted from the monitored dumps exceeded prior estimates by a factor of roughly 2. One site alone, the Brown Station landfill, spewed greater than 9 times more methane than the values reported by the Environmental Protection Agency’s Greenhouse Gas Reporting Program, even though the landfill gas collection and control system was in operation on the site.

The study also found that the region’s natural gas system—another major source of pollution—accounts for 40%–60% of the region’s methane emissions. The researchers have been working closely with the Maryland Department of the Environment to get the best possible inventories so that the state can reach its rigorous greenhouse gas reduction goals.