Some dam GHG emissions ‘on par with fossil fuels’ — study

Source: By David Iaconangelo, E&E News reporter • Posted: Sunday, November 17, 2019

Hydropower plants can have greater impacts on the climate than fossil fuel facilities during their first few decades of life, potentially undermining the technology’s usefulness, according to a study published this week in the American Chemical Society’s peer-reviewed journal.

The authors, who are climate scientists with the Environmental Defense Fund, compared data from 1,473 hydropower plants in 109 countries with the global median greenhouse gas emissions of other energy technologies.

Overall, hydro’s associated greenhouse gas emissions made the technology worse for the climate than nuclear, solar and wind power, but better than coal and natural gas per unit of energy generated, the study in Environmental Science & Technologyconcluded.

But that advantage over fossil fuel generation could disappear depending on the site’s characteristics, the study found. When reservoirs flood landscapes around the hydro facility, plants decompose underwater, causing the release of carbon dioxide and methane.

Those emissions tended to be concentrated in the first 10 years of a hydro generator’s life, a finding that could be important for avoiding climate “tipping points,” wrote the authors.

“Hydropower has outsized near-term impacts because of the methane emissions that strongly trap heat but don’t last for long in the atmosphere,” said Ilissa Ocko, a co-author of the study.

Methane can “yield a powerful amount of warming in a short period of time,” she said.

The research differed from many past analyses by shrinking the time span examined — accentuating the near-term climate effects from methane — and by considering the initial flooding of the reservoir.

The study’s results were “not consistent with the well-established narrative” about hydro, which is “broadly assumed” to be as clean as wind power, wrote Ocko and her co-author, Steven Hamburg.

“[W]e find that there are enormous differences in climate impacts among facilities and over time,” they wrote, observing that some are “even on par with fossil fuels.”

LeRoy Coleman, a spokesman for the National Hydropower Association, dismissed the study as “convoluted in its rationale” and “not a strong basis for informing” policy.

Methane emissions associated with the creation of reservoirs was “not centered on hydropower generation itself,” he wrote in an email to E&E News.

Coleman also pointed to a 2018 analysis of 500 global reservoirs from the International Hydropower Association that turned up a smaller emissions footprint for hydro than for utility-scale solar power.

“Hydropower is not a major source of greenhouse-gas emissions. The real story is that hydropower is critical to achieving deep decarbonization of our electricity system and meeting federal and state clean energy goals,” he said.

The study published this week found that in the United States, hydro’s climate effects were usually far smaller than those of fossil fuels, especially if it didn’t require a new reservoir.

Typically, there was “a good chance that hydro in the U.S. will be relatively low-carbon,” wrote Ocko in an email to E&E News.

But 42 of the 341 U.S. hydro plants studied would be worse for the climate than coal over the next few years, and 11 others would be worse than natural gas on a per-megawatt-hour basis, she said.

Every global region had hydropower sites where the climate impacts exceeded those of coal and natural gas.

That was especially true in some countries where a lot of new hydropower is slated to come online. In India, power generation from the technology could grow 230% through 2040. Of the 50 Indian facilities included in the study’s database, half were found to carry bigger near-term climate impacts than coal or natural gas.

In the United States, hydropower accounts for over 40% of all renewable generation and 7% of the total electricity mix, according to the Energy Information Administration. Its share has fallen in recent years amid rapid growth of solar and wind.

Hydro has been at the forefront of energy policy debates in the U.S. Northeast, where officials in various states have struggled to advance plans to import power from Canada.

The Energy Department is also interested in its potential as a non-intermittent source of renewable power. One 2016 estimate noted that hydro facilities could provide 150 gigawatts of electricity in the United States, up from just over 100 GW at present.