On the first of March, the LA Times published a story about the recent accelerating increase of methane in the atmosphere which began to rise, after a lull, in 2007. Fossil fuel burning and gas leakage results in "heavy" methane, and the research sought to but could not determine whether the rising percentage of "light methane" is accounted for by agricultural practices or natural processes. The scientists were also unable to conclude whether it could be attributed to a loss of atmospheric reactions that break down methane, although they do not believe it is from permafrost melt.
This flurry of concern is due to the alarming fact that if this rise in methane is not properly identified so that it can be halted and reversed, there is no way to stay within even the dubious safe limits for temperature increase outlined in the Paris accords - no matter what is achieved by way of CO2 reductions - due to the much intensified impact methane provides as a greenhouse gas.
This research hardly began with that study in Global Biogeochemical Cycles; Fred Pearce summarized several similar avenues of pursuit in a 2016 e360Yale article which likewise conclude that the increase is due to microbial emissions as opposed to fossil fuel, biomass burning, or (so far) permafrost release.
Since I have been concerned for over ten years that trees of all species are dying prematurely, everywhere around the earth, from absorbing pollution - a global trend that is utterly ignored by climate scientists, foresters, and atmospheric physicists alike - it occurred to me that there might be a connection between the inability of scientists to account for increased methane and their universal ignorance of widespread forest decline due to ozone.
I remembered a 2012 study in the Yale Forest that found "outwardly" healthy but diseased trees were emitting methane in "flammable concentrations" - which they refused to acknowledge meant something was terribly awry even though this is a quote from the Yale newsletter article :
Diseased trees in forests may be a significant source of methane that causes climate change, according to a study by researchers at the Yale School of Forestry & Environmental Studies (F&ES) published in Geophysical Research Letters.
“If we extrapolate these findings to forests globally, the methane produced in trees represents 10 percent of global emissions,” said Xuhui Lee, a co-author of the study and the Sara Shallenberger Brown Professor of Meteorology at Yale. “We didn’t know this pathway existed.”
The trees producing methane are older — between 80 and 100 years old — and diseased. Although outwardly healthy, they are being hollowed out by a common fungal infection that slowly eats through the trunk, creating conditions favorable to methane-producing microorganisms called methanogens.
...and so I decided to see if anyone else had found similar results.
Google is such a good friend because it turns out that yes, yes indeed, other researchers have detected methane being emitted by trees, but their results are generally shrouded in obscurity. This is what happens to ecological studies, in contrast to climate change research, due to deep-seated biases and consequent lack of funding.
A March 2017 article in Science Daily describes research of a plot in Maryland and proclaims:
A new study from the University of Delaware is one of the first in the world to show that tree trunks in upland forests actually emit methane rather than store it, representing a new, previously unaccounted source of this powerful greenhouse gas.
The other mechanism that could be causing methane fluxes from trunks is internal rotting or infection inside the tree, which produces an environment where methanogenic bacteria can survive and then methane diffuses out of the tree.
At this moment, the mechanisms of methane production in upland forests are not clear. 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...The research quoted above was published in the journal Ecosystems and has an extensive list of references. Knowledge of this goes back to at least 1974 when the magazine Science published "Methane Formation in Living Trees: A Microbial Origin" which stated:
Visibly healthy hardwood trees located on poorly drained soils contained high pressures of methane. Heartwood from these trees was water-soaked, neutral to alkaline in pH, fetid in odor, and infested with a diverse population of obligately anaerobic bacteria. the bacterium responsible for methane formation in tree. was isolated and characterized as a member of the genus Methanobacterium.
In January, 2018, an article was published titled "Scientists were long baffled by a methane surplus in our atmosphere. The culprit? Trees" about two studies of wetlands, one in the Brazilian Amazon and one in North Carolina, in which both find trees are significant sources of methane unaccounted for in climate budgets. That wetlands produce methane is well known due to anaerobic conditions; other forests that are silently but inexorably dying are potentially a much vaster source.
In 2009, in Global Change Biology, the abstract for a study about ozone's impacts on trees said:
The northern hemisphere temperate and boreal forests currently provide an important carbon sink; however, current tropospheric ozone concentrations ([O3]) and [O3] projected for later this century are damaging to trees and have the potential to reduce the carbon sink strength of these forests...This implies that a key carbon sink currently offsetting a significant portion of global fossil fuel CO2 emissions could be diminished or lost in the future.
Between the loss of a critical CO2 sink, and the unmeasured increase of forest methane emissions, the ongoing massacre of trees will ensure the 6th mass extinction proceeds much faster than even the most dire expectations. Methane-fueled wildfires will rage...and the scientists will continue to be puzzled.