Plants Compete with Cows and Bugs to make Methane?
by Jacob Gordon, Nashville, TN on 01.17.06
In a discovery that turns a major climate assumption on its head, researchers at the Max Planck Institute for Nuclear Physics have observed something that has escaped notice since scientists began understanding what methane is and how is behaves. It has been assumed until now that biogenic methane is the product of microorganisms and insects digesting organic matter. It now appears that plants themselves create the gas as well. Max Planck scientists estimate that plants account for up to a third of the methane in the earth’s ecosystem. Because methane is a strong greenhouse gas, second only to carbon dioxide, and a commonly used fuel, this discovery could have significant implications for issues of climate change. :: Max Planck Institute for Nuclear Physics
Think tanks already are using this study to spin arguments against those who think cliimate change calls for mitigative action: like using more biofuel. RealClimate has an excellent overview and fascinating comments about the work. Areas to be explored by corroborating investigations: not all major plant groups or growing regions are represented; anaeobic soil processes may not be represented, and so on. More interesting work ahead.
Plants (or at least trees; I can't say this is true for grass) still have a net carbon uptake; a tree may put out methane, but in the long run, the tree stores away more carbon drawn from the air than it puts out as methane. However, it is more complicated than simple carbon ballance. If I remember correctly, methane's infra-red absorption coeficient is 1,000 times higher than that of carbon dioxide. If a plant don't consume over 1,000 times more carbon dioxide than it puts out as methane, then planting such a plant will have a net negative impact if what you want is to mitigate global warming.
I may be mistaken about the "1,000 times" remark, but in any case, the key isn't to think of trees and forests as producing methane, but to consider their benefits as a whole: habitat, defense against errosion (and tsunamis, in the case of mangroves), and net reduction of greenhouse gasses--if indeed they consume enough carbon dioxide to offset the impact from the methane they produce.
Methane is 21 times more potent than CO2 on the whole, based on methane's much higher infrared absorption and its shorter atmospheric lifetime (12 yrs, compared to 50-200 for CO2).
www.epa.gov/globalwarming/publications/emissions
...and scroll down to "Greenhouse Gases and Global Warming Potential Values, Excerpt from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2000"
the methane output of trees only offsets the carbon storage capability of the trees by 1 - 4% (refer the original research and their subsequent update). Therefore we need to plant up to 4% more trees.
For some follow-up from the Max Planck folks, see their recent : http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/2006/pressRelease200601131/index.html