LIVESTOCK producers can rest easy. A recent surge in methane gases in the atmosphere has nothing to do with cows and sheep belching more.
CSIRO researcher Dr Paul Fraser says increased ice-melting in high latitudes in the Arctic and ozone recovery in the atmosphere are the most likely causes.
"The livestock industry is not implicated," he said.
A new study by Dr Fraser and US and UK researchers has found that after eight years of near-zero growth in atmospheric methane concentrations, levels have started rising again.
"This is not good news for future global warming," he said.
Methane is the second most important greenhouse gas in the atmosphere after CO2. It is emitted from natural wetlands, rice fields, cattle, forest and grassland fires, coal mines, natural gas leakage and use, and other sources.
"Over the past decade these methane sources have been close to balancing the absorption of methane through atmospheric oxidation and into dry soil," Dr Fraser said.
"This fragile balance has resulted in little growth of methane in the atmosphere."
Some sources have been increasing, such as from fossil fuel use, cattle, and rice, while others have been decreasing, particularly natural tropical wetlands.
"However, over the past year, the total sources have overwhelmed the total sinks, and methane has again started to rise."
Dr Fraser said the rapid growth in methane in the atmosphere over the past year was geographically concentrated, ruling out livestock as a source.
"The highest releases have been at high latitudes in the northern hemisphere, which experienced a very warm summer in 2007," he said. "Such increases have been predicted as rapid Arctic ice melting creates more high latitude wetland sources."
There also appeared to be greater methane emissions in tropical areas, which could reflect a recovery in ozone in the atmosphere, lower oxidation and less atmospheric absorption of methane, Dr Fraser said.
The results of the research, done in collaboration with the Massachusetts Institute of Technology and Bristol University, is being published today in Geophysical Research Letters, a journal of the American Geophysical Union.
