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Oh great - scientists just confirmed a key new source of greenhouse gases
From: "Dave Farber" <farber () gmail com>
Date: Thu, 29 Sep 2016 10:42:11 -0400
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From: Hendricks Dewayne <dewayne () warpspeed com> Date: September 29, 2016 at 10:24:46 AM EDT To: Multiple recipients of Dewayne-Net <dewayne-net () warpspeed com> Subject: [Dewayne-Net] Oh great - scientists just confirmed a key new source of greenhouse gases Reply-To: dewayne-net () warpspeed com Oh great — scientists just confirmed a key new source of greenhouse gases By Chris Mooney Sep 28 2016 <https://www.washingtonpost.com/news/energy-environment/wp/2016/09/28/scientists-just-found-yet-another-way-that-humans-are-creating-greenhouse-gases/> Countries around the world are trying to get their greenhouse gas emissions under control — to see them inch down, percentage point by percentage point, from where they stood earlier in the century. If everybody gets on board, and shaves off enough of those percentage points, we just might be able to get on a trajectory to keep the world from warming more than 2 degrees Celsius above the temperature where it stood prior to industrialization. But if a new study is correct, there’s a big problem: There might be more greenhouse gases going into the atmosphere than we thought. That would mean an even larger need to cut. The new paper, slated to be published next week in BioScience, confirms a significant volume of greenhouse gas emissions coming from a little-considered place: Man-made reservoirs, held behind some 1 million dams around the world and created for the purposes of electricity generation, irrigation, and other human needs. In the study, 10 authors from U.S., Canadian, Chinese, Brazilian, and Dutch universities and institutions have synthesized a considerable body of prior research on the subject to conclude that these reservoirs may be emitting just shy of a gigaton, or billion tons, of annual carbon dioxide equivalents. That would mean they contributed 1.3 percent of the global total. Moreover, the emissions are largely in the form of methane, a greenhouse gas with a relatively short life in the atmosphere but a very strong short-term warming effect. Scientists are increasingly finding that although we have begun to curb some emissions of carbon dioxide, the principal greenhouse gas, we are still thwarted by methane, which comes from a diversity of sources that range from oil and gas operations to cows. The new research concludes that methane accounted for 79 percent of carbon dioxide equivalent emissions from reservoirs, while the other two greenhouse gases, carbon dioxide and nitrous oxide, accounted for 17 percent and 4 percent. “There’s been kind of an explosion in research into efforts to estimate emissions from reservoirs,” said Bridget Deemer, the study’s first author and a researcher with Washington State University. “So we synthesized all known estimates from reservoirs globally, for hydropower and other functions, like flood control and irrigation.” “And we found that the estimates of methane emissions per area of reservoir are about 25 percent higher than previously thought, which we think is significant given the global boom in dam construction, which is currently underway,” she continued. As Deemer’s words suggest, the study does not single out dams used to generate electricity — it focuses on all reservoirs, including those that are created for other purposes. It drew on studies on 267 reservoirs around the world, which together have a surface area of close to 30,000 square miles, to extrapolate global data. Reservoirs are a classic instance of how major human alteration’s to the Earth’s landscape can have unexpected effects. Flooding large areas of Earth can set off new chemical processes as tiny microorganisms break down organic matter in the water, sometimes doing so in the absence of oxygen — a process that leads to methane as a byproduct. One reason this happens is that the flooded areas initially contain lots of organic life in the form of trees and grasses. Meanwhile, as nutrients like nitrogen and phosphorous flow into reservoirs from rivers — being poured in by human agriculture and waste streams — these can further drive algal growth in reservoirs, giving microorganisms even more material to break down. The study finds that for these reasons, reservoirs emit more methane than “natural lakes, ponds, rivers, or wetlands.” “If oxygen is around, then methane gets converted back to CO2,” said John Harrison, another of the study’s authors, and also a researcher at Washington State. “If oxygen isn’t present, it can get emitted back to the atmosphere as methane.”And flooded areas, he said, are more likely to be depleted of oxygen. A similar process occurs in rice paddies, which are also a major source of methane emissions. [snip] Dewayne-Net RSS Feed: <http://dewaynenet.wordpress.com/feed/>
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- Oh great - scientists just confirmed a key new source of greenhouse gases Dave Farber (Sep 29)