Keppler's work on methane produced aerobically by green plants which was published early last year brought a substantial response of arguments both for and against the paper.
Recently Tom Dueck and colleagues have published in New Phytologist findings that they found no CH 4 emissions from plants.
This brought some interchange as reported on climate feedback at nature.
Both groups have criticized the other's choice of experimental method. Dueck says that Keppler's group kept plants in sealed plastic containers instead of flow chambers, and exposed them to sources of stress such as bright sunlight and high temperature, which could have produced methane as an artefact. Keppler retorts that the use of 13C is an artificial piece of chemical trickery with unknown effects on plant metabolism, and also argues that methane production can vary by up to three orders of magnitude between species.
Keppler says other teams will be publishing results that back him up on the methane; but Mike reports that at least one other team is siding strongly with Dueck
Now we see the publication from another team at Max Planck and the authors are some very heavy artillery.
Citation: Sinha, V., Williams, J., Crutzen, P. J., and Lelieveld, J.: Methane emissions from boreal and tropical forest ecosystems derived from in-situ measurements, Atmos. Chem. Phys. 7, 14011-14039, 2007
Abstract. Methane is a climatologically important greenhouse gas, which plays a key role in regulating water vapour in the stratosphere and hydroxyl radicals in the troposphere. Recent findings that vegetation emits methane have stimulated efforts to ascertain the impact of this source on the global budget. In this work, we present the results of high frequency (ca. 1 min−1) methane measurements conducted in the boreal forests of Finland and the tropical forests of Suriname, in April–May, 2005 and October 2005 respectively. The measurements were performed using a gas chromatograph – flame ionization detector (GC-FID). The average of the median mixing ratios during a typical diel cycle were 1.83 μmol mol−1 and 1.74 μmol mol−1 for the boreal forest ecosystem and tropical forest ecosystem respectively, with remarkable similarity in the time series of both the boreal and tropical diel profiles. Night time methane emission flux of the boreal forest ecosystem, calculated from the increase of methane during the night and measured nocturnal boundary layer heights yields a flux of (3.62±0.87)×1011 molecules cm−2 s−1(or 45.5±11 Tg CH4 yr−1 for global boreal forest area). This is a source contribution of circa 8% of the global methane budget. These results highlight the importance of the boreal and tropical forest ecosystems for the global budget of methane. The results are also discussed in the context of recent work reporting high methane mixing ratios over tropical forests using space borne near infra-red spectroscopy measurements.
As an amount equal to approximately 90% of the annual emissions (450 Tg year) is oxidized through photochemical reactions initiated by OH radicals in the troposphere,A 8-10 % source addition adds substantial uncertainty to the carbon credit industry and carbon offsets.
Or as David Lowe comments in National Geographic.
"And of course this also affects the understanding of the current conditions."
Lowe notes that any reassessment of current climate change models could include some interesting political ramifications.
For example, the Kyoto protocol—an international treaty designed to try and curb climate change—requires complex accounting that holds countries to specified greenhouse gas emissions limits.
"Several countries are counting their forests as vegetative sinks for carbon dioxide," he said.
"But are you absorbing more carbon dioxide than you are [possibly] releasing methane? I suppose that the Kyoto protocol accountants are going to be working overtime trying to figure that one out."