Plants beat sheep in burping methane

Dr Chris de Freitas

New research that identifies plants as a source of the greenhouse gas methane is startling and could have implications for the Kyoto Protocol, says a leading scientist.

The research, carried out in Germany and published in the journal Nature yesterday, found that plants produce 10 per cent to 30 per cent of the methane emitted into the atmosphere each year.

Methane is the second most prolific greenhouse gas after carbon dioxide and is subject to emission controls under the Kyoto Protocol.

An estimated 600 million tonnes of methane are produced a year by sources including decaying rubbish and vegetation, flatulent livestock, wetlands, and coal mining.

It was not known previously that methane emissions occurred in living plants with oxygen present.

Dr David Lowe, a scientist at the National Institute of Water and Atmospheric Research, was asked to review the findings for Nature and said they would undoubtedly shock the scientific community.

"This really is a great surprise right out of left field," he told the Herald last night.

"No scientist who works in this area expected it."

The German researchers estimated that live vegetation produced between 63 million and 243 million tonnes of methane a year, but Dr Lowe said that statistical variations in the way methane emissions were calculated meant the total could be double that.

The journal said the findings potentially changed the way reforestation and livestock were treated in Kyoto's methane budgets.

Under the treaty, reforestation since 1990 can be used as a carbon dioxide sink to offset greenhouse gas emissions from other sources.

"We now have the spectre that new forests might increase greenhouse warming through methane emissions rather than decrease it by sequestering CO2," Nature said.

In countries such as New Zealand with large numbers of sheep, cattle and other livestock, methane constituted a large proportion of total greenhouse gas emissions.

Ruminant animals tended to graze on pastures that were originally forested, so given the findings, "it is possible that the forests that once occupied pasture may have produced as much methane as ruminants and grasses on the same land," the journal said.

Dr Lowe warned that further research was needed before too much was made of the implications for climate change or the Kyoto Protocol.

"It's not doom and gloom. It's just nature," he said.

"There are all sorts of things we don't understand about the planet."

He suspected that methane emissions from plants were less than the amount of carbon dioxide plants absorbed, but said further studies were needed to test the theory.

"We in New Zealand need to do research on this forest source of methane."

The Ministry for the Environment said the news would have no immediate impact on the Kyoto Protocol.

Dr Leonard Brown, the ministry's manager of reporting and review groups, said current standards were set until 2012.

He said the findings explained "a missing piece of the methane balance" but would require much more detailed study before any inclusion in the Kyoto Protocol.

"How it will actually impact New Zealand or other countries hasn't been looked at," Dr Brown said.

 

The kyoto protocol: Two opposing points of view

* Dr de Freitas, associate professor of Auckland University's school of geography and environmental science and a critic of the Kyoto Protocol, said the research challenged "alarmist" views on global warming.

"It's a wake-up call that we should be more circumspect about how we go about making policy on climate change."

Dr de Freitas said the research contradicted scientific assumptions about methane and could change the way forests were viewed under the Kyoto Protocol.

"We've always treated forests as a sink," he said. "Now forests actually produce as much methane as a flock of sheep."

The implications were profound for New Zealand.

"If our forests are also methane, we can't say we are going to grow forests to offset our burning of fossil fuels."

He said the findings warranted further research and added a refreshing angle to the highly political climate change debate.

"It'll be a cat among the pigeons," he said.


* Steve Abel

The Greenpeace spokesman on climate change said the research provided greater understanding of methane but did nothing to change conventional wisdom on global warming.

"It would be a big mistake to read this as a wiping of the slate of climate change science."

He said that carbon dioxide from human activity remained the main source of greenhouse gas emissions and that it was wrong to suggest forests were no longer key to managing climate change.

"The importance of growing forests as a sink for carbon dioxide is not challenged at all by these findings."

Nor were forests in the same league as livestock when it came to contributing to greenhouse gases.

"That doesn't give any recognition of the amount of carbon dioxide that growing plants sequester."

Mr Abel said the focus needed to be on reducing the burning of fossil fuels.

"That's the place we must get real gains if we're to avert the catastrophic effects of climate change."