Efforts by many countries to reduce their carbon footprint by building hydroelectric dams could be misbegotten should these facilities also prove to be a major source of greenhouse gas emissions.

While dams have long been believed to make a major contribution to reducing carbon emissions by enabling the generation of renewable energy in the form of hydropower, researchers now suspect they could be one of the world’s leading sources of greenhouse gas emissions.

The reservoirs created by dams generate copious amounts of methane as a result of the bacteria that thrive in their oxygen-deprived environments.

These microbes are essentially the same as those that occupy the intestinal tracts of bovine livestock and human landfills, emitting methane instead of carbon dioxide after consuming organic carbon to produce energy.

While it has long been known that these microbes make artificial lakes and reservoirs a major source of anthropogenic methane, scientists now believe that previous research grossly underestimated the volume of their emissions.

It was previously believed that reservoirs accounted for around one fifth of all man-made methane emissions. A study conducted by researchers from the National University of Singapore, however, notes that many of these assessments have been fraught with uncertainty.

In the paper Uncertainties of Carbon Emissions from Hydroelectric Reservoirs, Siyue Li from NUS’s Institute of Water policy and X.X. Lu from the university’s Department of Geography points out that global methane emissions from all large dams could be as high as 104 teragrams a year.

This is a staggering volume given NASA’s estimate that the total amount of methane entering the atmosphere globally as a result of the burning of fossil fuels  – the chief source of such emissions the United States, is within the range of 80 and 120 teragrams annually.

It would also make reservoirs a major contributor to climate change, given the significance of methane as a greenhouse gas.The Intergovernmental Panel on Climate Change estimates that around 25 per cent of anthropogenic climate change is the result of methane emissions.

Should reservoirs truly prove to be copious methane producers, however, it will bode poorly for concerted efforts by developing economies to reduce their greenhouse gas emissions by expanding their usage of hydropower.

A recent study led by Dr. Christiane Zarfl at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin found that rising demand for clean energy from renewable sources has prompted a surge in hydropower development following a protracted plateauing of growth.

The world is currently host to an unprecedented number of hydropower dam projects, primarily in the developing economies of Asia, Latin America and Africa.