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The transmission line, which would bring power from Canadian hydroelectric dams to New York City, was approved by regulators this month. New York’s plan to achieve a zero-emissions grid by 2040 depends on hydropower, and it’s not alone.
Hydropower is the largest renewable energy source worldwide. It makes up 7% in electricity generation in the United States. 37 states allow hydropower to be included in their renewable portfolio standards. These standards establish requirements for the amount of renewable energy that must go into electricity generation.
Hydropower will play an even greater role in the global effort to reduce fossil fuels and increase renewable energy.
There’s just one problem: A growing body of research published over the past two decades has found that most reservoirs, including those used for hydropower, aren’t emissions-free.
“Hydroelectric reservoirs are a source of biogenic greenhouse gasses and in individual cases can reach the same emission rates as thermal power plants,” Swiss researchers found in a 2016 studyPublished in the journal PLoS ONE.
Despite the green reputation that hydropower has earned among policymakers and others, some reservoirs can still emit large amounts of methane along with smaller amounts of nitrous dioxide and carbon dioxide.
That’s bad news because we already have a methane problem. This short-lived, but powerful gas is 85 times more likely to cause global warming than carbon dioxide over the next 20 years. If we want to prevent catastrophic warming, Scientists sayWe must reduce methane quickly. But new data show that despite this warning it’s still Record highs — even with a global pledge signed by 100 countries to slash methane emissions 30% by 2030.
While methane can be produced from wetlands or other natural sources, most of the emissions are from human-caused sources such as oil and gas, landfills, and livestock. We’ve known about the threat from those sources for years, but emissions from reservoirs have largely been either uncounted or undercounted.
In part that’s because tracking emissions from reservoirs is complicated and highly variable. Emissions can vary from one day to the next. They’re influenced by how the dam is managed, including fluctuations in the water level, as well as a host of environmental factors like water quality, depth, sediment, surface wind speed and temperature.
Recent scientific research has provided a better framework for this critical accounting. And environmental groups say it’s time for regulators to get busy putting it to work.
In the United States “there are no policy requirements and no regulatory requirements that reservoir emissions be assessed and reported,” says Kelly Catlett, director of hydropower reform at American Rivers.
And that’s concerning, says Daniel Estrin, general counsel and advocacy director at Waterkeeper Alliance. “We think hydropower is a totally false solution to the climate problem and would really dramatically exacerbate problems for our rivers’ biodiversity.”
Dams can block free-flowing rivers, causing a variety of harms. Fish, Freshwater musselsOther animals.
Gary Wockner, executive Director of the river advocacy group Save the Colorado, likens the current push for more hydropower to fracking, which was once thought of as a low-emissions “bridge fuel” to ease transition between fossil fuels and renewables.
“But as the science evolved, we now know that’s not true,” he says. “In some cases, with all the leaks of methane, fracking can be worse than coal. And so here we are again in essentially a similar situation with hydropower as the science continues to evolve.”
That’s why this March his organization, along with outdoor retailer Patagonia and the nonprofit Earthjustice, started pushing regulators for more accountability. These groups were joined by more than 100 other signers (including The Revelator’sCenter for Biological Diversity, parent organization I have written to the Environmental Protection AgencyTo begin a rulemaking to add dams and reservoirs to the Greenhouse Gas Reporting Program.
The program currently requires 8,000 facilities to report their greenhouse gas emissions — but none are hydropower plants or other reservoirs. The United States has 90,000 dams. 2,500 of these provide hydropower.
“Just like we require coal-fired power plants and natural gas power plants to report their emissions, I think we should require hydropower systems to report theirs,” says Mark EasterColorado State University senior research associate, who studies greenhouse gas emissions, is a backer of this petition effort.
It’s hard now to sidestep the issue of reservoir emissions if you’re serious about cutting greenhouse gases.
In the 1990s, the first research into the topic was conducted in Canada and Brazil. In the years that followed, research continued with a 2000 StudyBeing the first to take a wider view of the issue. In2013 Another StudyResearchers found that 10% have higher carbon dioxide emissions than equivalent amounts from gas-powered power plants.
The issue got a big bump in the public’s consciousness in 2016, when major media outlets picked up a Published study on global reservoir emissions BioscienceWe now know that methane emissions are the second most important contributor to climate changes.
The researchers urged policymakers across the world to take note and concluded that global reservoirs account for just under a gigaton of annual carbon dioxide equivalents — about 1.3% of all global emissions.
They also warned that their estimates may underestimate reservoir emissions. While most studies focus on emissions over a period of 100 years, methane has a greater impact on the short-term. There are also multiple pathways for methane to reach the atmosphere from reservoirs, some of which weren’t captured in their research but could be major contributors in certain places.
If areas are flooded to create a reservoir of water, microbes begin to decompose the submerged organic matter. This process can result in methane, carbon dioxide, and nitrous oxide emission depending on the water quality. Methane is produced when oxygen is low.
Early studies monitored the release of methane from reservoirs. But recent research has found that it can also bubble to the surface sporadically — a process that’s enhanced when reservoir levels are lowered. These fluxes can now be captured using new acoustic instruments. Additional emissions can occur downstream of water passing through dam turbines. These turbines draw water from the most methane-rich areas of a reservoir.
“Much more methane either bubbles out of reservoirs or is emitted just downstream from reservoirs than was previously known,” found the researchers of a 2021 StudyThe G-res tool was developed as a new framework for calculating reservoir emission.
They found that global reservoirs are able to emit 29% more greenhouse gas per area than previously calculated.
Methane emissions are a bigger concern in tropical climates where there’s more biomass and warmer temperatures, the study found. But additional research has revealed that more temperate climates like the United States aren’t immune from the problem, either.
A 2014 studyJake J. Beaulieu, EPA scientist, found that Ohio reservoirs can emit methane similar to those in the tropics. “We estimate that CH4 [methane] emissions from agricultural reservoirs could be a significant component of anthropogenic CH4 emissions in the U.S.,” the researchers wrote.
Six years later, Beaulieu and other researchers discovered that methane emissions from Ohio reservoirs were the cause of the death of Beaulieu. state’s fourth largestSource of methane from humans. That’s because nutrients continually wash into reservoirs from the upstream watershed. The nutrient runoff from reservoirs near agriculture and developments can lead to algae blooms that increase methane production.
“Reservoirs draining watersheds that are subject to high levels of nutrient loading, such as fertilizer application to croplands, tend to have higher methane emission rates than reservoirs draining undeveloped watersheds,” Beaulieu explained in an email to The Revelator.
This means that methane emission from reservoirs can be expected to rise with climate change. Warmer waters produce more algae. Increased storms and runoff will also send more nutrients to rivers and impoundments created from dams. This creates a vicious cycle of more methane emissions, more warming, and more algae.
Scientists’ work in advancing the methods to calculate greenhouse gas emissions from storage reservoirs is helping to drive real-world action. And it’s coming at a critical time.
Numerous new dams have been proposed by utilities and governments around the world. Many of these would be constructed in areas that have the highest levels of greenhouse gases, such as subtropical and tropical regions.
“What you could be worried about is the fact that there are hydropower building booms going on in South America, Southeast Asia, Eastern Europe and Africa,” says Tonya DelSontroCo-author of the 2016 article was, an assistant professor at University of Waterloo Bioscience study. “If you build these large water surfaces for reservoirs, then we’d be increasing emissions.”
The Intergovernmental Panel on Climate Change (IPCC) could take some steps to help. A 2006 report from the IPCC on climate change included an appendix “that gave some crude method to estimate greenhouse gases from reservoirs,” says Yves Prairie, an aquatic ecologist who holds the UNESCO chair on global environmental change at the University of Quebec. “But because it was in an appendix, it was never formerly adopted as a method and countries didn’t have to report their greenhouse gas emissions from reservoirs.”
However, the large body of scientific research done since then — including the G-res tool developed by Prairie and colleagues — led the IPCC to adopt a new methodology in 2019 that draws on these advances. It’s expected that soon countries will be required to report their reservoir emissions in their annual greenhouse gas inventories, he says.
Wockner, who started a petition to the EPA, hopes that reporting on emissions will soon begin in the United States.
“Then you can start talking about what to do about it,” he says. “How do you regulate emissions or how do you stop them?”
It could take several months for the EPA to respond to their petition. Even then, it could decide to not take any action. Beaulieu reports that EPA is already working on other angles to address the issue, including a nationwide survey of U.S. reservoirs’ greenhouse gas emissions.
The four-year project, scheduled to be completed next year, “will improve our understanding of how reservoir greenhouse emission rates vary,” he says.
The EPA also included reservoirs in their national greenhouse gas inventory, which is the first time this has been done. Newly published report.
This is encouraging news. “Emissions must be fully accounted for in the U.S. greenhouse gas inventory and evaluated in the context of regulatory compliance,” says Easter.
This information on emissions would be useful to other agencies in making decisions about whether to permit new dams or remove or relicense existing dams. It also helps to understand the environmental impacts of dams. It could also help states like New York to increase their clean energy portfolio by using hydropower.
“Having a peer-reviewed scientific process for tracking emissions would help not just dam operators, but regulatory agencies and the public, too,” says Easter. “That way they can understand where the issues are — and where they aren’t — to be able to make informed decisions about whether to maintain these systems or if alternatives need to be found.”
Promise or peril? Importing hydropower to fuel the Clean Energy Transition
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