How 'Clean' is the College's Hydroelectricity?

How 'Clean' is the College's Hydroelectricity?

In September of 2007, Holy Cross, in tandem with over 650 other colleges and universities, signed the American College and University Presidents’ Climate Commitment. This commitment meant that the College pledged to become carbon neutral (to have a net-zero carbon footprint) by the year 2040. In a move to minimize emissions from electrical usage, Holy Cross invested in hydroelectric power from TransCanada, a North American energy company. In the fiscal year 2014, following the College’s investment in hydropower, Holy Cross claimed a 44% decrease in its carbon footprint, the bulk of which came from this investment in hydroelectric power. Because it purchases hydropower, Holy Cross now considers its electrical usage to be emissions-free. And yet, a number of undesirable side effects arise from the use of hydroelectric power. These effects could even be negative enough that they call into question whether hydropower is the clean-energy panacea the College believes it to be.


Hydropower is the most commonly used source of renewable energy in the world today, accounting for more than 16% of global electrical production. In the United States, 66.8% of renewable energy comes from hydropower. Despite its undisputed status as a source of renewable energy, hydropower has come under considerable scrutiny in recent years as the scientific community continues to question whether it constitutes a clean source of energy. As utilization of hydropower has spread throughout the world, scientists have identified three key problems which stem from its use:

  1. The production of significant amounts of methane.

  2. A decline in biodiversity in the areas surrounding hydroelectric installations.

  3. Forced human resettlement in order to construct hydroelectric installations.

For the purposes of this article and the investigation of Holy Cross’s production of greenhouse gas emissions, only the first of these three problems is relevant to us. Therefore, I will spend the remainder of this piece exploring the possibility that the College’s use of hydroelectric power produces more than zero parts per million (ppm) in greenhouse gas emissions.  

How Hydroelectric Dams Produce Emissions: The Science

According to prominent environmental scientists such as Professors Townsend-Small, Ivan Lima, and Philip Fearnside, not only do hydroelectric dams produce more than zero ppm in emissions, they also emit abundant amounts of methane—an incredibly potent pollutant, the negative effects of which dwarf those of carbon dioxide. This process of emitting methane (sometimes in massive amounts) begins with the creation of the reservoir constructed behind hydroelectric dams.

Pictured above is a diagram of the stereotypical hydroelectric dam.  (Source: US Department of Energy)

Pictured above is a diagram of the stereotypical hydroelectric dam. (Source: US Department of Energy)

When building the reservoir behind such dams, construction teams flood a newly created basin in the ground and the surrounding area with water in order to produce the water pressure needed to power hydroelectric dams. As this occurs, organic matter from the surrounding land—such as plants, algae, and detritus—flows into the reservoir and steadily builds up. In the absence of a steady, natural current to move this material around, nothing actively works to prevent or disperse such a buildup of matter. In some cases, runoff from the agricultural lands typically alongside these reservoirs and dams contribute to the further accumulation of organic matter therein.

Scientists have documented this phenomenon closely, and observe that it occurs at most hydro dams in Brazil and China, and at some in the United States (take the Harsha Lake Dam in Cincinnati, Ohio, for example). Because the runoff from the agricultural fields in these countries almost always contains fertilizer (or other substances rich in nutrients that enhance plant growth), once runoff reaches a reservoir, the nutrients from it help the accumulated organic matter grow. As these oxygen-depleting organisms develop and spread, they create algae blooms in a process known as eutrophication. Algae—like the matter already sapping oxygen from the reservoir’s water supply—requires additional oxygen to sustain itself, leading to an increasingly precipitous decline in the levels of oxygen available in the reservoir.

In the context of hydropower dams, methane is produced by reservoir-dwelling microbes that thrive in such environments with highly depleted oxygen levels. These environments, also known as hypoxic zones, provide fertile feeding ground for these microbes because they consume the organic matter there in order to acquire energy. After harnessing the carbon in this matter, these microbes respire methane. University of Cincinnati biogeochemist Amy Townsend-Small explains: “microbes eat organic carbon from plants for energy, just like people and other animals, but instead of breathing out carbon dioxide, they breathe out methane. These same types of microbes live in the stomachs of cows and in landfills, which are other sources of methane to the atmosphere.”

Townsend-Small believes that these agricultural reservoirs “are a larger source of atmospheric methane than we had thought in the past.” Despite the noble, even clean, intent behind them, the reservoirs behind hydro-powered dams essentially become vast pools of methane-releasing toxins.

How Hydroelectric Dams Produce Methane: The Cases of India and Brazil

In 2007, Ivan Lima and his colleagues at Brazil’s National Institute for Space Research conducted a study that further called into question hydropower’s status as a clean source of energy. The data they published shows that “the world’s 52,000 largest dams release 104 million metric tons of methane annually.” Assuming these calculations are accurate, this means that hydro-powered dams account for a total of 4% of man-made emissions. This would make them the largest source of anthropogenic methane production in the world—and these shocking numbers do not even include the 4,500 hydro-dams found in India! Because the world considers it a developing nation, India has not been required to cut its emissions. Ivan Lima projects, however, that the combination of “methane released from reservoir surfaces, spillways, and turbines” in India would render the country’s greenhouse gas emissions 40% higher  than current estimates show. 

The case of Brazil presents us with similar, disturbing conclusions. In 2004, Philip Fearnside—a scholar at the National Institute for Research in the Amazon and a leading expert in the analysis of net emissions—conducted a study of Brazilian hydro-dams in which he stated that “if degassing emissions were factored in at several large hydropower plants in Brazil, then these dams would be larger contributors to global warming than their fossil fuel counterparts.”Indeed, researchers suggest that all large reservoirs globally could emit up to 104 teragrams (104 trillion grams) of methane annually. By comparison, NASA estimates that global methane emissions associated with burning fossil fuels result in the emission of  80-120 teragrams (80-120 trillion grams) of methane annually.

Why Methane is so Problematic; What we Must Demand Moving Forward

At this point, it is clear that some, if not all, hydro-dams emit methane. Some emit copious amounts of it. So why is this bad? Why should methane emissions prompt Holy Cross to reconsider its investment in hydroelectric power, to reevaluate its calculation that hydropower produces “net-zero emissions”? Because methane (CH4) is a particularly pernicious greenhouse gas.

When comparing CH4 to carbon dioxide (C02) in terms of its contribution to climate change, CH4 reveals itself the greater contributor. Although the half-life of CO2 is double that of CH4, CH4’s ability to trap heat far exceeds C02’s ability to do so. Over a 100 year period, CH4 is 25 times more effective at trapping heat and radiation in the atmosphere than C02 is. As human activity continues to release massive quantities of CH4 into the atmosphere, our world will only continue to become warmer, our weather more extreme. The longer we wait to curb methane emissions, the quicker these climatic changes will take hold.

In light of the harmful effects of methane and the irrefutable proof that hydroelectric dams often produce this gas, we must ask ourselves—as Crusaders, as men and women for others, as people who seek to hold the College to its word—the following question: has Holy Cross invested its money in an energy source worse than the fossil fuel it sought to abandon?  Even if hydropower is cleaner than the fuel oil no. 2 formerly used by the College, does hydropower actually reduce the College’s emissions to zero ppm? We must demand to know more.

Those responsible for Holy Cross’s investment in hydroelectric power may claim that the hydro-dams mentioned above were located in areas with high levels of vegetation, and thus cannot be compared to the hydro-dams used by the College. These individuals might claim that TransCanada’s dams are not located in similar environments, and thus will not produce as much (if any) methane. Below are images taken from TransCanada’s website showing the location of two of their hydro-dam/stations in the northeastern United States. The first of these is located in Searsburg, Vermont; the second is located in Connecticut on the First Connecticut Lake.

A bird's eye view of the Searsburg Dam and Reservoir.  (Source: Google Earth)

A bird's eye view of the Searsburg Dam and Reservoir. (Source: Google Earth)

Connecticut's First Connecticut Lake Dam and Reservoir.  (Source: Google Earth)

Connecticut's First Connecticut Lake Dam and Reservoir. (Source: Google Earth)

These images show the high levels of vegetation (organic matter) surrounding both stations. Because the hydroelectric dams which Holy Cross uses to produce our electricity can be found in the same environments as those dams which emit methane, we must ask if the dams used by the College also emit methane. If they do, how much methane do they produce?

In the event that the College’s hydro-dams produce any methane, the administration must revise its claim that its electrical usage produces zero emissions. Holy Cross has an obligation to fulfill its carbon neutrality pledge. We must, therefore, be certain that our use of hydropower places the College on the right track to accomplish this goal. If it does not—if hydropower does, in fact, produce emissions—the College should begin to explore other sources of clean energy, such as solar or geothermal power.

Hydropower may be better than coal or other fossil fuels, but it might not be the perfect answer to the College’s electrical needs.  

(Overhead photo: Hydro Equipment Association)

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