February 28, 2005
Do Hydroelectric Dams Cause Global Warming?

For years hydroelectric dams have shown up on lists of energy sources that are renewable and non-polluting. Environmental complaints about dams have been over more local considerations such as the fact that dams can disrupt fish spawning and that the dams contribution to water evaporation by increasing the surface area over which water can evaporate. Well, Philip Fearnside of Brazil's National Institute for Research in the Amazon says that dams increase the amount of plant matter that decompose in anaerobic condtions and produce methane which is 21 times more potent as a greenhouse gas than carbon dioxide.

In a study to be published in Mitigation and Adaptation Strategies for Global Change, Fearnside estimates that in 1990 the greenhouse effect of emissions from the Curuá-Una dam in Pará, Brazil, was more than three-and-a-half times what would have been produced by generating the same amount of electricity from oil.

This is because large amounts of carbon tied up in trees and other plants are released when the reservoir is initially flooded and the plants rot. Then after this first pulse of decay, plant matter settling on the reservoir's bottom decomposes without oxygen, resulting in a build-up of dissolved methane. This is released into the atmosphere when water passes through the dam's turbines.

Note that a dam in Brazil which is right on the equator is probably going to receive a lot more plant matter from a river that fills its reservoir than would a dam on a river further from the equator. Even if some hydroelectric dams turn out to be net producers of greenhouse gasses we can't assume that all hydroelectric dams cause more in warming effects from methane production than they prevent in avoided carbon dioxide release.

Methane is a valuable gas to capture in situations where it can be captured because methane can be burned for the energy. Also, the burning of methane turns the carbon in it into a compound (carbon dioxide) that is far less potent as a greenhouse gas.

Parenthetically, James Hansen of NASA has been arguing for several years that reduction in methane emissions would reduce global warming effects more cheaply than lowering carbon dioxide emissions (and see more on this here and here). I especially like his argument that lowering methane emissions would both increase air quality down at ground level where we live and decrease greenhouse warming effects. Hansen still thinks carbon dioxide emissions restrictions will be necessary. But why not first implement the far cheaper option of decreasing methane emissions and also get better ground level air quality in the bargain? Just the increase in ground level air quality alone would, in my opinion, justify the costs. Efforts to capture methane would be at least partially paid back because the captured methane could be burned for energy.

Update: Dave Schuler mentioned methane production from agriculture in the comments. I can't answer his question about the relative contribution agriculture makes to methane emissions. But this reminds me of recent research at the University of California at Davis which showed that most methane from cows comes from cow belching.

California dairy cows produce only half the amount of certain air pollutants as had been believed and, perhaps more important, most of a dairy cow's contribution to smog comes not from her fresh manure, but from her belching, according to preliminary findings by a UC Davis scientist.

Those unexpected results may affect the thinking and practices of California regulators and dairy operators trying to reduce air pollution.

"We have to re-think the idea that the only good solutions are engineering solutions, and consider biological avenues such as animal feeding and management to reduce emissions," said Frank Mitloehner, the UC Davis air quality specialist who is conducting the study.

For three months, Mitloehner and his co-workers have studied dairy cows in sealed environmental chambers to simulate emissions from one type of cow housing, known as freestall conditions. Under these controlled conditions -- the first study of its kind -- the researchers were able to collect precise measurements of the volatile organic compound (VOC) emissions that cows and their fresh waste produce.

"For the first time we can tell dairy farmers the source of VOCs from the cow-housing part of their dairy," Mitloehner said. "For the most tightly regulated pollutant, the 700 ozone-forming gases collectively called volatile organic compounds, that source is not the cows' fresh waste. It's the cows."

This result makes methane emissions reduction easier to do than was previously thought. Supplements of bacteria types or compounds that inhibit methane production could be placed in cow feed to reduce methane production. But the idea of changing feedstocks as a way to reduce methane emissions from cows is nothing new and I've come across mentions of research along these lines in Switzerland, France, Australia, and New Zealand. In NZ agricultural scientists are experimenting with different types of grasses to lower methane production in grazing animals. They found substantial differences in methane production depending on which grass was fed to animals. (and the CH4 mentioned below is methane)

Improving the quality of the diet of ruminants tends to result in higher feed intakes, which in turn tends to increase productivity and CH4 output per animal. However, if CH4 is expressed per unit of product, then using a smaller number of high-producing animals to produce a given amount of product emits less CH4 than using a larger number of lower producing animals. This is because a smaller proportion of the feed eaten is required to maintain the animal and because high feed intakes tend to reduce CH4 yield per unit of feed eaten. Concentrate diets produce less CH4 than forage diets but are too expensive for extensive use in New Zealand. Research undertaken by AgResearch and Dexcel indicates that certain forage species e.g. white clover, lotus and sulla, improve animal performance and produce less CH4 per unit of feed eaten. Experiments are currently underway to look at whether ryegrass cultivars selected for improved animal performance also result in lower CH4 yields per unit of product.

One can easily imagine a great reduction in agricultural methane production by seeding pastures and farm fields with grasses that are found to reduce methane production of cows. Countries willing to genetically engineer grasses to add factors that reduce methane production will be able to achieve the greatest reduction in agricultural methane emissions. This will probably turn out be a fairly cheap and easy way to reduce methane emissions.

Agricultural scientists Garry Waghorn and Michael Tavendale of AgResearch Grasslands in New Zealand have found that higher levels of condensed tannins in grasses reduce methane production.

Methane is either burped or expelled out in breath, and is a by-product of the fermentation of feed in the rumen. Dr Waghorn and Dr Tavendale say about 90 percent of all methane emissions come from ruminants. Greenhouse gases affect everyone, because the Government is committed to ratifying the Kyoto Protocol. Once the agreement is signed, New Zealand will face financial penalties if it exceeds the emissions it recorded in 1990. But, and this is the dilemma for the country, if agricultural production expands, so will gas emissions. Condensed tannins are a naturally occurring compound found in red wine, apple skins and cocoa, as well as some pasture grasses, including lotus and sulla. They can also be found in docks, white clover flowers and some seeds. Besides reducing methane emissions, condensed tannins have other animal-related benefits, including improved milk yields, increased liveweight gain, decreased internal parasite burden and reduced bloat, dags and fly strike. Dr Waghorn said tannins had in the past been considered "evil" because some plants, especially tropical ones, contained them in high concentrations, which were bad for animals. But in a temperate climate such as New Zealand's, condensed tannins werefound in "weedy species", or less common plants, he said. "It's unusual to find it in grasses, which is a problem because animals eat grass," Dr Waghorn said.

But in some reports I came across condensed tannins reduced methane emissions by only 15%. Tannins alone might not be a panacea.

Whereas reportedly only 2 percent of greenhouse gas effects in the United States come from agriculture New Zealand has only 4 million people but 10 million cattle and 45 million sheep. Therefore most of New Zealand's greenhouse gas emissions come from agriculture.

"New Zealand is unique in that over 50 percent of its greenhouse gas emissions arise from methane released by enteric fermentation," said Katharine Hayhoe, an atmospheric scientist at the University of Illinois, Urbana-Champaign, Illinois.

Therefore it is not surprising that New Zealand agricultural scientists are especially interested in reducing methane emissions from cows and sheep.

Share |      Randall Parker, 2005 February 28 12:58 AM  Energy Tech

Dave Schuler said at February 28, 2005 8:34 AM:

I wonder how large the effects of hydroelectric dams in methane production are relative to commercial livestock production . And of, of course, lots who people who emit methane, too.

rsilvetz said at February 28, 2005 11:51 AM:

Well, I'm always a little perplexed at all the global warming fuss.

As a matter of geologic history we are between ice ages -- thank the Gods for that.

As a matter of living, global warming radically increases both arable and livable land.
E.g. Siberia -- soon to be the best real estate around!

As a matter of sunspot cycles and longer sun cycles, that hot globe in the sky is outputting more energy -- so of course it's warmer down here.

Cows might be great generators, but has anyone quantified termites? How many billions of organics come from the recycling of wooden structure by termites?

In any event, human activity, may or may not have some impact, but quite frankly, the system itself is pushing the temp.

Just my 2cents. Dime? ...with inflation...

Fly said at February 28, 2005 5:24 PM:

Off Topic: But might be of interest.

Breakthrough in solar photovoltaics


Kurt said at March 1, 2005 11:34 AM:

this whole global warming thing is getting quite out of hand. Its getting to the point that "it causes global warming" is becoming as meaningless as "it causes cancer". Its gotten to the point that everything causes global warming in the same way that everything causes cancer.

Perhaps the whole global warming thing is bunk.

Rew said at March 1, 2005 4:48 PM:

Re-Cow Belching. Aussie research has developed gut innoculant to improve digestion and reduce methane emission. Saw on TV.

back40 said at March 1, 2005 7:08 PM:

Rew has it. The issue is the metabolic pathways used by anaerobic bacteria. If we are going to hack genomes or direct evolution it is bacteria rather than forage species that we would get the most benefit from. Once developed, they would be of use in the soil, in wetlands, in rice paddies and land fills as well as rumens. It's the easier way, the faster way and the cheaper way.

Jamie Johnson said at March 3, 2005 11:56 AM:

It all boils down to the fact that humans don’t understand atmospheric science and geologic process enough to speculate what causes global warming/cooling phases. Well, we don’t know enough as we think we do. We can assume, but how do you prove something that takes thousands/millions of years to happen? Even with geologic and ice records projections are spotty. We cant even predict el nino/la nina events, let alone atmospheric conditions on a planetary scale.

However, I’d like to see more hard evidence that shows the release of CH4 into the atmosphere from reservoirs as well as records from varying countries versus the release of CO2, CH4, and other VOMs from Curuá-Una. Im not so sure that the water that gets pumped through the turbines is from the bottom of the reservoir, which is where most of the CH4 would be, therefore large quantities wouldn’t get released into the air. Also, when plants decompose the CO2 doesn’t just bubble out, it also forms H and OH ions with the water...all this is contained in sludge at the bottom of the body of water which remains in place if the body of water is deep enough. Gas exchange would probably vary from area to area, depending on local weather conditions and how stagnant the water is too.

Tony Chesser-Evans said at March 14, 2005 1:42 PM:

I'm more interested in whether or not there's some way we can recover the methane. I mean, landfills generate methane, too, but there are efforts underway to tap that methane and produce electrical power from it ("landfill gas" is typically about 50% CO2, so you can't just turn around and sell it as natural gas; it's cheaper to just burn it in a gas turbine, resulting in a bunch of CO2 and a bunch of electricity).

The big deal here is that vegetation covered by the reservoir decomposes in an anaerobic environment, making methane, which is dissolved in the water in the reservoir, then released into the atmosphere after it goes through the hydroelectric turbines. If we can find some constructive way to tap the methane at the hydroelectric turbines (methinks we're talking dissolved gas forming bubbles as a result of cavitation around the heavily-loaded turbines), we could stop dumping the methane into the atmosphere and put it to other, constructive uses. IIRC, Natural Gas is anywhere from 88-94% methane. Since it has the highest hydrogen-carbon ratio of all the hydrocarbon fuels, it's relatively clean-burning stuff.

Indeed, CO2 from the atmosphere is processed by vegetation in some areas near the reservoir, which is then covered when the reservoir goes through its seasonal expansion, and methane is produced. You could think of this as a seasonal method of sequestering CO2 and making useful fuel from it.

Come on, people. Let's find a way to make this into a POSITIVE thing. While we can't very well capture the methane coming from livestock (or co-workers who had beans or cabbage for lunch), we're probably talking about large enough volumes here that it might be worth it.

JJ said at April 1, 2005 6:41 AM:

if it causes global warming and is higher levels in methane why can't we just us solar panels? this is weird.

Jocelyn 3 said at April 1, 2005 6:46 AM:

i think if our ansesters could live with out electricity we can to its just so retarted

brian said at April 13, 2005 5:54 PM:

Little late to this post but,
Dear Jocelyn 3,
Our ancestors had shorter life spans, often times literally ate garbage when starving and fought more wars over misunderstood/misused resources. Are you seriously suggesting that going back to that is an answer in this day and age?
Can energy resources be used more wisely? Certainly. Will that be accomplished by turning your back on understanding how to do so?
Hardly. Even suggesting that is an answer in a one liner points to a real retardation.

Steven Brockerman said at April 13, 2005 7:29 PM:

#1 greenhouse gas is WATER VAPOR.

Methane makes up less than .0036% of the atmosphere.

Atmospheric temps, based on NASA sat & baloon data indicate temps have dropped .1 C over the past 35 years. As for the .7 C rise in surface temps over the past 100 years of NWS data, see the Little Ice Age during the mid to late 19th century. I surely hope they increased!

As for going way back, temps higher than today -- and CO2 levels higher -- during Roman Empire & Middle Ages.

100 to 500 thou yrs ago -- well, there were those ice ages.

3 million yrs. ago, we're waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaay cooler now.

Recommend you refer to environmental *scientists* (for instance, Mueller at Berkley, Lidzen at MIT) before you draw your hasty conclusions.

*Sigh* Global Warming -- the email hoax that just won't die.

James Hague said at October 19, 2005 9:15 PM:

If the history of the earth consists of 5 billion years, but temperature has only been consitantly recorded for a couple hundred, how can they say that in the grand scheme of things there is a potentally deadly rising temperature? Have they recently uncovered the temperature of the alleged other 4,999,999,800 years? Unless the above is true, they have little to compare it to.

Keegdog said at November 4, 2005 6:33 AM:

If methane is caused by the decoposition of the plants at the bottom of the reservoir, why don't we strip the land of the vegetation before construction of the dam? If that is not reasonable, then there must be some way to trap the methane under the water.

StupidPaper said at November 5, 2005 7:42 AM:

The hydroelectric dams produce more electricity and is better than oil. Oil pollutes the enviorments more than hydroelectricity, and people and animals produce methane, if what you say is true, then the world would have been warming up since millions of years ago, because animals showed up. If you're going to write a paper, get your research done first.

pepito princewill said at January 5, 2006 7:08 AM:

I would like to know why hydrocarbons vary from area to area.secondly, i would also like to know the most important physical properties of crude oil and why is it so?

magoogles said at May 14, 2009 3:08 PM:

All u guys suck my balls

global warming exists!

Suwanto said at August 6, 2010 2:03 AM:

Adapt to global warming!
Stop global warming? are you playing Moses??

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