Editor-in-Chief Brian Calvert described dams as “providing clean hydropower” (“Compromise amid the canyons,” HCN, 9/4/17). Actually, a spate of new research shows that there is basically no free greenhouse-gas lunch when it comes to generating electricity, and the burden of hydropower is increasingly coming into focus. The news is not good. For example, a recent peer-reviewed study published in the journal PLOS ONE predicts that the greenhouse gas emissions from Lake Mead, compared against the hydropower it produces, are as bad as burning coal on a kilowatt-hour basis.
Reservoirs are basically methane factories, and methane is a potent greenhouse gas, carrying more than 80 times the warming effect of carbon dioxide on a pound-per-pound basis. Reservoirs contain a stew of microbes that feed on organic matter in the water column, and in the deeper depths where oxygen is depleted, the microbes release methane as a by-product of their metabolism. Concentrations can reach extremely high levels in the depths from which water is channeled into the turbines that produce hydroelectricity. Once that methane-rich water exits downstream, it’s off-gassed into the atmosphere, where it joins the increasingly dangerous mix of greenhouse gases that are radically warming our planet. Manufacturing the concrete used in constructing hydroelectric dams also carries a giant burden of emissions that silently continue warming the planet for centuries to come.
Mark Easter
Fort Collins, Colorado
This article appeared in the print edition of the magazine with the headline No free lunch for hydropower.
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