In the fight to cut greenhouse gas emissions, we tend to think of trees as our allies, but new research suggests they might not be as "green" as we give them credit for. Researchers at the University of Delaware have found that some types of trees actually emit methane through their trunks, partly countering their role as a greenhouse gas sink.
Though it comprises a smaller percentage of greenhouse gases than carbon dioxide, methane makes up for it in potency, with its effects on the environment estimated to be 25 times stronger than CO2. Climate scientists have been trying to catalog sources and sinks of methane and CO2 to take stock of the Earth's greenhouse gas budget and find ways to improve it.
Oceans and forests are generally considered sinks, meaning they capture and store greenhouse gas emissions, but they aren't completely offsetting the gases burping out of the Arctic, reservoirs and livestock.
To study how much methane and carbon dioxide forests may be producing or storing, the University of Delaware team took to the woods in Cecil County, Maryland. Over a growing season spanning April to December, they used a tool called an Off-Axis Integrated Cavity Output Spectroscope (OA-ICOS) to analyze whether soil, tree trunks and coarse woody debris (CWD), or the rotting wood on the ground, are sources or sinks.
The biggest surprise the team found was that trees give off methane through their trunks. The amount depends on the species, but generally those emissions don't seem to be as high as their carbon dioxide output.
"The tree trunks constantly have low but detectable emissions of methane," says Rodrigo Vargas, lead researcher on the study. "Soils are providing an environmental service of sequestering this potent greenhouse gas, but the trunks are releasing methane equivalent to four percent of what could be captured by CWD and soils at the ecosystem scale."
Where trees are pulling that methane from remains unknown, but the researchers believe the clues point to one of two sources: the trees might be absorbing it from the soil through their roots, or the wood has already begun to rot from the inside.
"At this moment, the mechanisms of methane production in upland forests are not clear," says Vargas. "Methane can be either transported from the soils upward inside the stem and diffused to the atmosphere or produced inside the stem by fungi or archaea — single-celled microorganisms."
CWD was found to swing wildly between being a methane source and sink, and it seems to depend on its age. Since these fallen bits of wood are essentially the middleman between living trees emitting methane, and the soil absorbing it, the older a piece was, the more likely it was to be absorbing the gases.
"When a tree falls over, it's still functionally the same in terms of methane emissions," says Daniel Warner, lead author on the study. "Over time, as it decays, my theory is that it gets colonized by soil bacteria that consume methane and it shifts to behave more like the soil, resulting in a methane sink."
Since these findings are based on one section of forest, the researchers plan to investigate whether they carry across to other forests and types of trees, and whether that emission footprint is large enough to factor into global methane models.
"When people develop ecosystem to global scale methane budgets, there's always a chunk in which it is uncertain from where that methane is coming," says Warner. "Methane emissions by vegetation and tree trunks are seen as a newly-considered source that might bring that budget closer in to our estimates. It's good to keep chipping away at that."
The research was published in the journal Ecosystems, and Warner demonstrates the work in the video below.
Source: University of Delaware
Before you permit yourself to get all scare-defied over more methane being released into the atmosphere, and even if you buy into recent (since WWII) surface temperature rise being as a result of increased greenhouse gasses, do your research and find that methane is an irrelevant gas in the theoretical causes because of the limited bands of energy from which it can possibly absorb and from those two bands upon which it can act, it must share that potential with one more prevalent, which has already done the job almost completely in those bands leaving nothing much for methane to work upon. Those who promote gloom & doom from impending release of stores of methane wrongly assume the gas would have unlimited stores of energy upon which it could draw to heat the planet should that release occur. Therein lies the failure of this sub-theory even assuming such release is possible and imminent. There is no such pool of energy.
The energy beamed by the sun comes to Earth in the form of short waves, is absorbed by the planet, and some is transmitted back to space in the form of long waves in various bands of energy. Warmists' Anthropogenic Global Warming Theory holds that greenhouse gasses intercept by absorption and transmit back to Earth a percentage of the long wave radiation energy in natural balance until humans destroy the balance by over supplying unnatural amounts of greenhouse gasses by which such process and added heat causes more of the principle greenhouse gas, water vapor, to be produced accelerating the process in an ever heightening loop of heating Gaia. Methane is a "greenhouse gas." The misnamed process acts nothing like a greenhouse, BTW, and empirical measurements, the acid test of science, do not reflect water vapor increasing as required in proportion to CO2 increases or even out of proportion. No increase of water vapor at all in fact has been measured among the several failures of the theory to be sustained by empirical measurement.
Methane (CH4) by its physical properties has only two narrow absorption bands at 3.3 microns and 7.5 microns in the overall broad electro-magnetic spectrum from which it can absorb energy. Theoretically, CH4 is 20 times more effective an absorber than CO2 – in those bands in a laboratory. However, CH4 is only 0.00017% (1.7 parts per million) of the atmosphere. Moreover, both of its bands occur at wavelengths where H2O is already absorbing virtually all energy. Because water vapor is much more plentiful in the atmosphere than methane (or any other GHG), H2O absorbs vastly more energy and is by far the most important greenhouse gas. On any given day, H2O is a percent or two of the atmosphere (1.0-2.0% or 5,882 to 11,764 times as prevalent as methane in the atmosphere, or 5882÷20=294.1 [or 588.4] multiple the absorber as methane); we call that humidity. Hence, any radiation that CH4 might absorb has already been absorbed by H2O in the only radiation bands methane absorbs energy. Once the energy in a band of the spectrum has been sucked dry, no additional absorptive gas can absorb more. Painting a black window another coat will not keep out more light. In other words, the ratio of the percentages of water to methane is such that the effects of CH4 are completely masked by H2O because the absorption of infrared energy in the bands of the spectrum affected by methane has already been saturated by H2O absorption. The amount of CH4 would have to increase 100-fold to make it comparable to H2O and even then it would no longer matter because water vapor has beat it to the punch.
There is not much ambient energy in those two little short, stray bands of the radiation spectrum to start with and most of that has already been worked over by H2O from time immemorial leaving only the scraps to poor CH4, which can never effect climate to any appreciable or worrisome amount. Because it absorbs energy in a laboratory does not mean it works that way in a chaotic atmosphere with other agents and processes present.
Learn more of what the science neophytes should have investigated before fearing methane, which is an irrelevant greenhouse gas (graphs, observed facts & all that tedious math kind of stuff) —
http://wattsupwiththat.com/2014/04/11/methane-the-irrelevant-greenhouse-gas/
http://www.americanthinker.com/articles/2015/01/whit_house_methane_madness.html
http://wattsupwiththat.com/2015/10/10/stop-the-devastation-of-peoples-lives-by-speculating-with-no-data-remembering-cattle-and-methane-emissions/
Methane is fine vehicle to instill fear, the politicians greatest ally, on an uninformed populace though. It is the rare person whose knowledge on the substance reaches even the level of understanding the stuff coming from their gas stove is raw methane much less how it works in the atmosphere...easy targets for manipulation.