Oh great - scientists just confirmed a key new source of greenhouse gases

["Dave Farber" <farber () gmail com>]

Begin forwarded message:

> 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]
>
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