METHANE IS A VERY POWERFUL GREENHOUSE GAS (MORESO THAN CO2) - AND IT'S ONE WHOSE AGRICULTURAL ORIGINS SCIENTISTS DON'T FULLY UNDERSTAND

NATURE:

Nearly two years after the confusing discovery that terrestrial plants may be pumping out methane through an unknown mechanism, scientists are still producing puzzling results about this strange phenomenon. A study this week seems to confirm that methane is emitted in this way, but adds that it might be limited to woody plants — again for unknown reasons.

Methane (CH4), the main component in natural gas, is a simple hydrocarbon and a potent greenhouse gas. It is most commonly released by organic matter decaying in oxygen-free environments, such as swamps and animal guts.

The original finding, published in January 2006, that green plants emit methane in the presence of atmospheric oxygen1 seemed to turn upside down textbook knowledge. It was clear that if global vegetation does release substantial amounts of the gas, one or more of the known methane sources must have been considerably overestimated (see The methane mystery).

But those initial measurements, by Frank Keppler of the Max Planck Institute for Nuclear Physics in Heidelberg Physics, Germany, have proven hard to verify. Using a different experimental approach, other researchers failed to find evidence for any significant ‘aerobic’ methane emissions by plants. In a study published in May2, Tom Dueck, then with Plant Research International in Wageningen, the Netherlands, and his colleagues concluded that the contribution of green plants to global methane emission is very small at most.

However, a Chinese–American team has now confirmed, with a very precise carbon-isotope method, that at least some plants do indeed emit measurable, if small, amounts of methane under aerobic conditions3. But the results suggest that the effect is not universal among plants.

... But the results are by no means definitive. Although Wang did not see emissions from herbaceous plants, Keppler did. And there is also some preliminary field evidence for the effect occurring over tropical grasses.
Confusion continues

“This is a difficult process to study,” says Jay Gulledge, a microbiologist at the University of Wyoming in Laramie and a co-author of the newest study. “It will take a lot more work to figure out when, where, and why it happens, and whether or not it is actually important to the global methane budget.”

Keppler had estimated initially that terrestrial plants could account for up to 40% of total methane emissions, but the figure has since been revised downwards. If the effect is not universal among plants it would imply an even smaller contribution to the global methane budget.

As yet, all global estimates are extremely uncertain. But even if plants contribute little to the global methane budget, scientists are keen to understand the unknown chemistry behind the elusive effect.

• THIS SHOULD MAKE IT ABUNDANTLY CLEAR THAT SCIENTISTS STILL DO NOT KNOW ENOUGH ABOUT 'WHAT CONTRIBUTES WHAT' TO THE ATMOSPHERE, AND THAT THEREFORE MODELING BASED ON WHAT THEY THINK THEY KNOW IS MERE GUESSWORK.

• WE SHOULD NOT MAKE WHOLESALE CHANGES TO OUR REGULATORY SCHEMES, OR TAXES OR OUR INDUSTRIAL BASE BECAUSE OF WHAT UNDER-INFORMED SCIENTIST AND ILL-INFORMED POLITICIANS GUESS MIGHT HAPPEN.