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The Methane Option

WorldChanging reader John Atkinson alerts us to an article in the current issue of the Proceedings of the National Academy of Sciences entitled "Greenhouse Gas Growth Rates" -- a fairly innocuous title for what could be a very important bit of research. In this article (which PNAS has made Open Access, Drs. James Hansen and Makiko Sato of NASA's Goddard Institute for Space Studies and the Earth Institute at Columbia University show that reducing methane (CH4) in combination with reductions in carbon dioxide (CO2) emissions would be both more feasible and more effective as a means of keeping global warming to 1-2°C over this century than reductions in either alone.

The argument is fairly straightforward: in order to prevent coastal flooding, global warming needs to be kept to 1-2° C above current averages; doing so via CO2 emissions controls alone would require that atmospheric CO2 be kept to below ≈440 ppm (parts per million) -- not much of an increase over current CO2 levels of around 375 ppm; but because methane is more powerful a greenhouse gas per molecule, by cutting methane emissions by 400 ppb (parts per billion) while reducing or keeping stable other fractional non-CO2 greenhouse gases (such as N2O, nitrous oxide), the CO2 limit rises to ≈520 ppm, a level which can be more readily achieved.

To be clear, this is not an argument that we can forget about controlling carbon dioxide. If CO2 concentration continues to rise at anywhere near its current pace, it will be impossible to avoid going above 2° and getting coastal flooding (and worse). At best, this idea is a lifeline to let us attack CO2 emissions -- the top priority -- successfully:

CO2 has accounted for 90% or more of the increased GHG climate forcing in recent years. In 2003, the portions of added forcing were CO2 (90%), N2O (5%), CH4 (4%), and MPTGs [Montreal Protocol Trace Gases] and OTGs [Other Trace Gases] (1%). Recent changes of CO2, CH4, and N2O growth rates are affected by short-term fluctuations of sinks as well as sources and are not necessarily indicative of future trends.

CO2 increases are the main cause of the increasing anthropogenic greenhouse effect, so efforts to mitigate global warming must focus on CO2. However, it would be a mistake to infer that CO2 forcings are unimportant relative to CO2. Future CO2 gas changes can be positive or negative, thus adding to or subtracting from the CO2 forcing. Given the difficulty of halting near-term CO2 growth, the only practical way to avoid DAI ["dangerous anthropogenic interference"] with climate may be simultaneous efforts to reverse the growth of some non-CO2 gases while slowing and eventually halting the growth of CO2. [Emphasis mine.]

Note the reference to Montreal Protocol Trace Gases: it turns out that many of the gases controlled by the Montreal Protocol (PDF) banning CFCs have greenhouse impact, too. As these gases are fully phased out, that fraction of greenhouse gas "climate forcing" will be eliminated. It also suggests a possible pathway for controlling methane and nitrous oxide -- adding them to the Montreal Protocol list of covered gases. In the meantime, the recently-announced Methane to Markets program will hopefully be a good initial step.

As recently as thirty years ago, methane was thought to be irrelevant to the climate. We now know it has an impact far greater than its relatively low concentrations might otherwise suggest. Methane is 21 times more powerful a greenhouse gas than CO2 (and nitrous oxide is 270 times more powerful). But because it cycles out of the atmosphere at a much faster rate than CO2, efforts to control methane emissions can have a more immediate impact. An excellent discussion of methane's role as a greenhouse gas can be found in this September 2004 NASA article.

I can't emphasize enough that parallel work on reducing methane does not mean putting off carbon dioxide reductions. As noted, continued rapid growth of CO2 concentration could make it impossible to avoid the 2° red line no matter what else we do, and recent research suggests that we may be getting warmer faster than expected. Hansen and Sato's article reminds us, however, that carbon dioxide is not the only greenhouse gas -- and that reminder may well be what lets us avert climate disaster.


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Comments (6)

Hopefully more diary farmers will begin using methane digesters to create energy and clean up after themselves. One of the most comprehensive and "beautiful" green-energy projects around, thanks to all of the benefits: cleaner water, plenty of energy from a renewable resources, pays for itself over a few years, reduces methane emissions, reduces smell around the farm... see 270 cows generating electricity for farm Methane digester also breaks down waste in the San Francisco Chronicle (May 2004).

Richard Chaput:

Oh ya...I remember methane.

So...how are we going to stop the world's permafrost from melting and releasing all their, well...you know

"estimate an increase in methane emissions of at least 20 percent, but maybe as much as 60 percent, from 1970 to 2000"

"The carbon locked up as methane hydrate in the earth's oceans and permafrost areas is double the amount of carbon in the combined reserves of oil, coal and conventional natural gas,"

Indeed. If you read the article, Richard, you'll see that prevention of unlocking permafrost methane is one of the goals of keeping the temperature growth down. Check it out.

This is a very interesting argument, which has actually been discussed by Jim Hansen before: there are several greenhouse gases being released by human activities, so why not consider policy options related to each of them? Methane may be easier to fix, in the short run, so why not do this first?

Here is the argument. Avoiding "dangerous" changes in climate (however you would define it) would probably require that we stabilize CO2 levels around 400-450 ppm, which means we would need an immediate "crash" program to move us away from fossil fuels. Even the most ambitious renewable and conservation intensive program will have a very, very hard time doing this without some severe economic disruptions. But concentrating on the other non-CO2 greenhouse gases (methane, N2O) first may be far easier and allow a little more transition time for us to phase out fossil fuels and CO2 emissions.

Methane, N2O, and CFCs would be a good place to start. But we still don't fully understand the natural sources and sinks of these gases (especially methane and N2O) in the biosphere and atmosphere, so it's hard to get a handle on the anthropogenic emissions. Starting with leaky natural gas pipelines (like those in the former-USSR) and coal mines would be a good start, of course. Why lose this methane, which could be used as fuel? (Burning methane does release CO2, but mole for mole CO2 is much less of a greenhouse gas then CH4.)

Other human sources of methane are probably related to rice paddies (probably hard to change?), biomass burning, landfills, sewage treatment, and livestock (easier to change with dietary adjustments). N2O is another issue altogether, but they could be reduced partly by using less nitrogen fertilizer on croplands. Reducing CFC emissions is another great idea, and this is already underway.

Another thing to keep in mind is the residence time of these compounds in the atmosphere. CO2 has a residence time of about 100-110 years, so it's a fairly long-lived greenhouse gas. Methane's residence time in the atmosphere is something like 9-10 years, so the concentration of methane in the atmosphere would respond much more rapidly to emissions changes. And unlike CO2, methane is actually destroyed in the atmosphere (by various photochemical reactions) and does not require (or directly respond to) sinks in the biosphere or oceans.

I think the take home point of this analysis is that there are multiple levers in the climate system -- not just CO2. Lowering methane (and other non-CO2 greenhouse gas) concentrations is probably easier to do now, while pushing hard on the long-term CO2 question. This probably buys us some more time, but it could also be another excuse for delay -- like some of the carbon sequestration proposals out there?

At the end of the day, I think we're going to need all of the help we can get: lowering methane (and other non-CO2 greenhouse gas) concentrations, slowing the rate of CO2 emissions (eventually bringing them back down, ultimately towards zero), and sequestering carbon in long-lived reservoirs (to buy time). There's no single "silver bullet" here, so let's work on all of them -- especially where there are win-win benefits for other problems, such as security, health and economics.

Jon F:

right on, dude. one interesting point re: carbon sequestration AND methane - check out this piece highlighting research into using methanogenic bacteria to clean up/eat up large CO2 deposits by converting them to methane, which would then of course be used for energy:


we're are still at a stage where we can't really pick 'winning' technologies in this - so yeah, 'let's work on all of them,' fossil fuel solutions may become 'renewable' or at least 'clean', and various clean/renewable technologies may end up competing for the same physical space/funding/whatever. let a thousand flowers bloom - especially considering the amount of time CO2 stays in the atmosphere, we have the 'luxury' of waiting for a few years at least to see which approaches work best.

(self-promotion: check out the energy news roundup I posted on Winds of Change earlier, http://www.windsofchange.net/archives/005923.php, for developments in all sorts of directions)

John A.,

Very interesting! I wasn't aware of the carbon-munching microbes work. That's very nifty!

Thanks also for the other links.


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