In this June 22, 2010 file photo, the Jean-Lesage hydro electric dam generates power along the Manicouagan River north of Baie-Comeau, Quebec. Credit: Jacques Boissinot / The Canadian Press via AP

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Bradford H. Hager is the Cecil and Ida Green Professor of Earth Sciences at MIT, where he does research on reducing greenhouse gas emissions. He lives in Mercer.

I once believed that all hydropower is clean. But recent research shows clearly that some hydropower is not. Unfortunately, the intuitively appealing notion that Québec can export clean power to Massachusetts and New York, as well as decarbonize Québec, no longer holds up to rigorous analysis. In light of recent peer-reviewed research it is clear that NECEC is unlikely to reduce global carbon emissions and may well increase them.

We now know that there is a huge range in greenhouse gas emissions of hydro reservoirs. Reservoirs in deep, narrow valleys, as in Switzerland, provide clean power. Shallow reservoirs flooding vast forests, as in Brazil and Québec, do not. This makes sense. Between 1971 and 2011, Hydro Québec flooded thousands of square miles of forestland, killing the trees that had been removing carbon from the atmosphere. These flooded trees and soil decay, releasing substantial CO2 and methane for decades.  

The Maine Public Utilities Commission conclusion that the New England Clean Energy Connect would prevent the release of over 3 million metric tons of greenhouse gas every year ignores the peer-reviewed science, from both independent and Hydro Québec scientists, that all of Hydro Québec’s reservoirs emit CO2 and methane. Instead, the PUC based its conclusion on the report of a consulting company, hired by Central Maine Power Co., that said that the power that NECEC would provide is emission-free. Although Hydro Québec has not corrected the PUC conclusion, it does acknowledge that there are substantial emissions from some of their reservoirs, particularly newer ones, but says that excess emissions from the decay of flooded vegetation go away after a few years.  Hydro Québec’s own measurements contradict that claim, and recent research  concludes that climate damaging emissions from the decay of flooded organic material may continue for over 50 years. Consider our experience in Maine: Logs continue to decay slowly at the bottoms of rivers half a century after the log drives ended.

Another worrisome change in our understanding of Hydro Québec’s emissions concerns methane, a greenhouse gas that has a warming effect 85 times greater than that of CO2 over the 20-year timescale important for climate change. Hydro Québec claims that methane is an issue for tropical reservoirs, but not their northern ones. Yet a paper published this year, co-authored by a Hydro Québec scientist, estimates that their methane emissions have a climate impact that is significantly greater than their already substantial CO2 emissions.

The most frustrating part of the discussion regarding the NECEC, including its permitting reviews, is that it considers only local greenhouse gas emission reduction. Climate science clearly shows that global warming results from total, not local, emissions. Merely shifting emissions from Massachusetts to Canada or elsewhere does not help the climate. Québec has surplus capacity during times of unusually high water, and in the winter it has sometimes needed to import power from neighboring provinces. Power generated by burning coal in the neighboring province of New Brunswick is much dirtier than the gas-generated power in Massachusetts that NECEC would replace. Using Québec’s hydropower to replace New Brunswick’s coal would be far more effective in fighting climate change than exporting it via the NECEC would be.

We urgently need solutions to the climate crisis, but they must be scientifically sound. We now know much more about carbon emissions from hydro than was known when Maine issued permits for the NECEC. The emissions from new reservoirs (Hydro Québec states it is not planning any now) are nearly as large as those of natural gas power plants, and five to 20 times those of solar and wind. Let’s try to ensure that wind and solar, which are both cheaper and much cleaner than new hydro, are the low carbon power sources of the future. We must not allow Hydro Québec to lock in infrastructure that would delay development of local wind and solar and set back the vital agenda to solve climate change.