RDRutherford

Methane emissions on the rise

Industrial greenhouse-gas increase has been masked by natural declines.Quirin Schiermeier

Swamp gas emissions are going down - for now - as industrial emissions go up. Punchstock

Current projections of methane emissions are likely to be too optimistic, an international team of atmospheric scientists reports today in Nature¹.

Methane, which is less abundant in the atmosphere than carbon dioxide but 20 times more potent as a greenhouse gas, is thought to have been responsible for up to one-third of global warming since the industrial revolution.

Unlike CO₂, however, atmospheric methane concentrations stopped rising in the 1990s, probably as a result of the sharp decline of the Soviet Union’s industrial power. Concentrations have remained relatively stable since 1999, giving the impression that human and natural methane sources and sinks may have reached a lasting balance.

But the most extensive study so far suggests this is not so: human-created sources are rising, but have been masked by natural declines.

The study has come too late to be included in the next Intergovernmental Panel on Climate Change (IPCC) report, due next year. This report actually reduces estimates of the effect of methane on future climate change as compared to the previous edition — a reduction that now seems to have been premature.

Back to source

The team behind today’s report, led by Philippe Bousquet, an atmosphere researcher at the Climate and Environment Science Laboratory in Saclay, France, looked at air samples from 68 measurement stations worldwide, taken between 1984 and 2003. They then used complex atmospheric modelling, along with information about the isotopic composition of the methane and how its concentration varied with the seasons, to work out where the gas had come from. The information allows for a meaningful assessment on a rough continental scale, says Bousquet. “In some places we don’t see very well, but we’re not blind.”

The decrease during the 1990s was indeed caused by a marked decline of emissions from human sources, such as coal mines and landfills, the study finds. But anthropogenic emissions have resumed their increase since 1999, probably because of the economic boom in China and other southeast Asian economies.

This rise has been concealed by natural trends. The world has seen a 5% decrease in flooded land, thanks to drought and land-use change. This has reduced the amount of methane produced by bacteria living in swampy lands.

Droughts also bring peat and forest fires, but such biomass burning seems to have released less extra methane than previous studies suggested.

“The big surprise is that wetlands, not fires, are the dominant contribution to changes in natural methane emissions,” says Bousquet. “That wetland reductions have as yet entirely masked the rise in human emissions is really not something we would have expected.”

Rising flood

The stabilization of atmospheric methane, although not a political achievement, has been a ray of hope amidst the growing concerns about global warming. The new findings may show that hope to be an illusion.

“Clearly, this is not good news,” says Jos Lelieveld, an atmospheric chemist at the Max Planck Institute for Chemistry in Mainz, Germany. “Wetlands cannot decrease forever.” Rather, wetlands are expected to become larger in northern regions, for example, as areas of permafrost melt. Scientists fear that this might release vast amounts of the greenhouse gas.

Fortunately, methane emissions are much easier to control than CO₂. Siphoning off methane from coal plants and landfills, or feeding farm animals different food so they produce less methane in their guts, doesn’t require large changes in our way of living, says Bousquet. Modernizing old coal mines could also help reduce deaths in industrial accidents in Asia.

“In my opinion the easiest and most time-effective way to control climate change is to start acting on methane,” says Lelieveld.

http://www.nature.com/news/2006/060925/full/060925-9.html

Published online: 5 September 2006; | doi:10.1038/news060904-5

Escaped Chinese GM rice reaches Europe

Prevalence of genetically modified foods highlights risks of field trials.Emma Marris

Some Chinese noodles may have been made with genetically modified rice. Getty

It has been just one week since the European Union ordered the United States to certify its rice exports as transgenic-free, in an attempt to stem the influx of herbicide-tolerant rice across the ocean. Now comes a report that genetically modified (GM) rice from China is already on supermarket shelves in France, Germany and the United Kingdom.

Greenpeace International, an environmental organization that campaigns against GM crops, said today that imported rice noodles in Europe contain rice with genes from the Bacillus thuringiensis (Bt) bacteria — genes that are often introduced to crops to help them fight off insects. The strain is not approved for human consumption even in China, but has somehow wandered out of field trials and into the food chain there (see ‘GM rice forges ahead in China amid concerns over illegal planting‘). Now it seems that processed foods made with the rice have made the trip across international borders.

Greenpeace says an independent, reputable lab has confirmed the presence of the genes. They add that the facility wishes to remain anonymous so that it will not be labelled as an activist lab. “They worry about being associated too closely with us,” says Jeremy Tager, a campaigner against GM crops who is based in Amsterdam, the Netherlands.

“It highlights the difficulty of controlling contamination,” says Tager. “Human error with so many people involved is quite a large possibility.”

It isn’t the first time that GM plants have escaped from field trials or the lab. Engineered golf course grass and Bt corn have been found in the wild, for example. And GM strains of rice containing a herbicide-resitance gene, called LL Rice 601, have recently been found in commercial samples of long-grained rice in the United States. The European Union last week introduced rules on rice certification to try and prevent such samples from reaching their shop shelves.

Allergic reaction

The Greenpeace release and report make much of the potential allergenicity of a compound, Cry1Ac, which is found in a pure or slightly altered form in the escaped Chinese GM rice. But Rob Aalberse, a biochemist at the University of Amsterdam specializing in food allergies, says that the risk is likely to be small. “There are no real data to indicate that there is any real risk involved.” Studies showing allergic effects in mice, cited by Greenpeace, did not cook the rice, which Aalberse says would decrease the allergenicity.

Besides, Aalberse says, the unapproved rice is already being consumed by many people in China. “If there were anaphylactic events, people would have noticed,” he says.

The real problem, says Aalberse, is containment. “Field trials are one thing, but if you are going to grow it for real, I think it will be impossible to contain it.”