The Conservation Law Foundation, a Boston-based environmental advocacy group, cited a report it commissioned from Synapse Energy Economics, that said the following:  “The science is clear that the reservoirs behind hydropower dams emit greenhouse gases, relative to the forests and wetlands they flood (which often take greenhouse gases out of the atmosphere).

An excerpt from their Report:

“Hydroelectric generation of electricity (hydropower) is commonly thought of as renewable, sustainable, and lacking in emission of atmospheric pollutants; however, these assumed benefits are rarely evaluated critically in the context of policymaking, as new reservoirs and dams are rarely proposed in North America, outside of Québec and Labrador.

This report reviews the state of information regarding one key policy consideration: how hydropower stacks up against other technologies with respect to greenhouse gas (GHG) emissions—including the life cycle emissions from the construction and operation of generating capacity. An important aspect of the analysis is a comparison of not only the “typical” amount of GHG emissions from each technology, but a presentation of the range of values that may be observed. The report also discusses concerns about the way GHG emissions are measured, especially in the case of hydropower, and best practices for doing so. Finally, the report discusses a specific policy consideration: the relative trade-off (from a GHG emission perspective) of Canadian hydropower imports versus other energy options for New England.”

Download the entire Synapse Energy Economics Inc. Report.