Dear Friends/Co-sailors,
In my today's pick section, sharing this just published
article by Bobby Magill. Hydropower projects are not really green projects, reinforces this article. It also brings some new perspectives into debate.
Some of my takes from the article are as follows:
- Until recently, it was believed that about 20 percent of all
man-made methane emissions come from the surface of reservoirs. New research suggests that figure may be much
higher than 20 percent.
- As per a 2013 study by researchers from Singapore, large
reservoirs globally could emit up to 104 teragrams of methane annually. By
comparison, NASA estimates that global methane emissions associated with
burning fossil fuels totals between 80 and 120 teragrams annually.
- Scientists have long thought reservoirs in warmer climates
in the tropics emitted more methane than reservoirs in cooler climates, but the
research at Harsha Lake shows that may not be the case.
- Warning from the Singapore researchers: Rapid hydropower development and increasing
carbon emissions from hydroelectric reservoirs to the atmosphere should not be
downplayed.
In fact, we have also been warning the same citing examples
of several other studies done so far on methane emission from man-made
reservoirs of hydro-power projects.
Hope you will find this interesting.
Thanks and regards,
Ranjan
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Hydropower May Be Huge Source of Methane Emissions
Bobby Magill, October 29th, 2014
Harsha Lake, a large reservoir near Cincinnati, Ohio, emitted as much methane in 2012 as roughly 5,800 dairy cows would have emitted over an entire year. Credit: Firesign/flickr
Imagine nearly 6,000 dairy cows doing what cows do, belching
and being flatulent for a full year. That’s how much methane was emitted from
one Ohio reservoir in 2012.
Reservoirs and hydropower are often thought of as climate
friendly because they don’t burn fossil fuels to produce electricity. But what
if reservoirs that store water and produce electricity were among some of the
world’s largest contributors of greenhouse gas emissions?
Scientists are searching for answers to that question, as
they study how much methane is emitted into the atmosphere from man-made
reservoirs built for hydropower and other purposes. Until recently, it was
believed that about 20 percent of all man-made methane emissions come from the
surface of reservoirs.
New research suggests that figure may be much higher than 20
percent, but it’s unclear how much higher because too little data is available
to estimate. Methane is about 35 times as potent a greenhouse gas as carbon
dioxide over the span of a century.
Think about man-made lakes in terms of cows passing gas:
Harsha Lake, a large reservoir near Cincinnati, Ohio, emitted as much methane
in 2012 as roughly 5,800 dairy cows would have emitted over an entire year,
University of Cincinnati biogeochemist Amy Townsend-Small told Climate Central.
Methane emissions from livestock are the second-largest source
of methane emissions in the U.S., behind crude oil and natural gas, according
to the U.S. Environmental Protection Agency. But the EPA’s greenhouse gas
emissions estimates do not yet account for methane emissions coming from
man-made reservoirs.
Part of the reason is that, generally, very little is known
about reservoirs and their emissions, especially in temperate regions, such as
in the U.S., where few studies have been conducted.
In 2012 study, researchers in Singapore found that
greenhouse gas emissions from hydropower reservoirs globally are likely greater
than previously estimated, warning that “rapid hydropower development and
increasing carbon emissions from hydroelectric reservoirs to the atmosphere
should not be downplayed.”
Those researchers suggest all large reservoirs globally
could emit up to 104 teragrams of methane annually. By comparison, NASA
estimates that global methane emissions associated with burning fossil fuels
totals between 80 and 120 teragrams annually.
But how much reservoirs contribute to global greenhouse gas
emissions is “still a big question mark,” because the issue remains relatively
unstudied and emission rates are highly uncertain, said John Harrison, an
associate professor in the School of the Environment at the Washington State
University-Vancouver whose research focuses on how reservoirs can be managed to
reduce greenhouse gas emissions.
“So I don’t think we really know what the relative
greenhouse gas effect of reservoirs is compared to other sources of energy in
the U.S.,” he said.
Research at Harsha Lake may help scientists better
understand how reservoirs contribute to climate change.
In a study published in August, Townsend-Small and
researchers from the EPA found that Harsha Lake emitted more methane into the
atmosphere in 2012 than had ever been recorded at any other reservoir in the
U.S.
“When you compare the annual scale of the methane emission
rate of this reservoir (Harsha Lake) to other studies, it’s really much higher
than people would predict,” EPA research associate and Harsha Lake study lead
author Jake Beaulieu told Climate Central.
Scientists have long thought reservoirs in warmer climates
in the tropics emitted more methane than reservoirs in cooler climates, but the
research at Harsha Lake shows that may not be the case, Townsend-Small said.
“We think this is because our reservoir is located in an
agricultural area,” she said.
Methane is generated in reservoirs from bacteria living in
oxygen-starved environments.
“These 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,” Townsend-Small said. “These same types of
microbes live in the stomachs of cows and in landfills, which are other sources
of methane to the atmosphere.”
Runoff from farmland around Harsha Lake provides more
nutrients in the water, allowing algae to grow, just like numerous other
reservoirs surrounded by agricultural land across the country.
Methane-generating microbes feed on decaying algae, which
means that lakes catching a lot of nutrient-rich agricultural runoff generate a
lot of methane.
“There are a very large number of these reservoirs in highly
agricultural areas around the U.S.,” Townsend-Small said. “It could be that
these agricultural reservoirs are a larger source of atmospheric methane than
we had thought in the past.”
Emissions from reservoirs in all climates could be
underestimated because of a discovery Beaulieu’s team found at Harsha Lake: The
area where a river enters a man-made lake emits more methane than the rest of
the lake overall.
Nobody has measured that before, Beaulieu said.
Most other research studying reservoir methane emissions
doesn’t account for how emissions may vary across the surface of a lake, he
said.
The EPA is about to begin a more comprehensive study
measuring methane emissions from 25 reservoirs in a region stretching from
northern Indiana to northern Georgia, with sampling beginning next year,
Beaulieu said.
That study will help the EPA eventually include reservoir
methane emissions in its total estimates of human-caused methane emissions.
Until that and other studies are complete, scientists can
only speculate on the impact hydropower is having on the climate.
“We’re still in the very early days here of understanding
how these systems work with respect to greenhouse gas production,” Harrison
said.
http://www.climatecentral.org/news/hydropower-as-major-methane-emitter-18246
