Plant Gas

Don:

I go to sleep one day knowing full well that trees help to lower any global warming that might occur due to increased CO2.  I was also under the assumption that cows were making much of the methane, which is a more potent hothouse gas than CO2.  I am comforted in knowing that if there is global warming, humans will invent a means of preventing it from going to extremes by fertilizing the oceans or some such thing.

When I wake up the next day, I read an article in Nature which states that trees emit between 10 and 30 percent of the total methane which is created on earth.  This contradicts basic assumptions about photosynthesis.  How did scientists miss this source of a huge amount of methane?  This means that the global warming models are all wrong.  It also means that the Kyoto agreement (which many nations are following including many US cities (see Al Gore’s new film)) which calls for planting trees to compensate for CO2 emissions is all wrong.

http://news.bbc.co.uk/2/hi/science/nature/4604332.stm

To their amazement, the scientists found that all the textbooks written on the biochemistry of plants had apparently overlooked the fact that methane is produced by a range of plants even when there is plenty of oxygen.

The amount of the gas produced increased when the air was warmer, and when there was more sunlight. The paper estimates that this unexplained phenomenon could account for 10-30% of the world's methane emissions.

The possible implications are set out in Nature by David Lowe of New Zealand's National Institute of Water and Atmospheric Research, who writes: "We now have the spectre that new forests might increase greenhouse warming through methane emissions rather than decrease it by sequestering carbon dioxide."

If this turned out to be true, it would have major implications for the rules of the Kyoto Protocol on climate change, which allows countries and companies to offset emissions from the burning of fossil fuels like coal and oil by funding the planting of new forests or the restoration of deforested areas.
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WalterB:

I have reviewed the original Nature sources of your comment.

This Letter to Nature (subscription required) does not alter the substance of the global climate change problem. If true, in the most extreme interpretation, it increases the danger of "global warming."

However, as pointed out in the article and Nature's summary, the total concentration of CH₄ is well known. It is elevated over tropical forests. Therefore, this Letter does not significantly change the contribution of CH₄ to greenhouse gases. It does suggest a change in the table of estimated contributions to CH₄ emissions.

What is most troublesome is the lack of mechanism for this finding. The temperature dependence suggests an inorganic mechanism, but the authors don't know what it could be. This is important, as without a mechanism, we do not know whether the finding would be replicated in the field, outside the laboratory. Simple measurement of CH₄ won't establish the hypothesis (that has already been done). The mechanism is required in order to trace the proposed kind of CH₄

While the interesting finding of this Letter should be followed up, it has so far been neither confirmed nor denied. So, right now, the answer is 'do nothing.' evolution under natural conditions.

I agree.  We should continue to cut down trees, which hold the carbon in sequestration, and use the wood to build furniture, houses and other buildings.  Meanwhile we can capture new carbon by replanting the forests.

Same thing we are doing now.