Southern Hemisphere methane levels increasing: Niwa

The amount of greenhouse gas methane in the southern half of the planet's atmosphere has increased 0.7% - or 35 times the output from New Zealand's livestock - from 2007 to 2008, according to measurements from the National Institute of Water and Atmospheric Research's (Niwa) Baring Head station. 

Niwa principal scientist Keith Lassey said New Zealand had a particular issue with methane, which accounted for about half of the country's greenhouse gas profile. This caused particular issues at international discussions, like those held in Copenhagen last week, he said.

It was also entirely coincidental the findings were released the day after the global summit on climate change wrapped up, he said, the report from the research institute's Baring Head station having been written over a six month period.

At their meeting in the Danish capital, the world's leaders reached no binding resolutions on reducing emissions contributing to climate change, but rather, agreed on some goals to aspire to. The meeting concluded at the weekend.

While much less methane was in the atmosphere than carbon dioxide, it was the second most important contributor to global warming, as it trapped 21 times more heat than CO2 over the same time period, Dr Lassey said.

The amount of the gas in the atmosphere had more than doubled since 1700AD, compared to any time over the previous 800,000 years. Weather patterns in Earth's atmosphere mixed all gases released quickly, thoroughly and everywhere, he said. Measuring stations in the northern hemisphere recorded slightly higher amounts of methane than the southern, as that was where most of the gas was produced, Dr Lassey said.

"Some [gases] have a short life-cycle, but this isn't one of them. Methane has a lifetime of about a decade," he told NZPA. "Typically, if a bucket load of methane is released in the northern hemisphere, some of it will reach us within a year. It doesn't respect boundaries."

Though scientists had recorded a lull in atmospheric methane from 1999 to 2006, measurements had jumped since 2007, he said.

Scientists thought this was partly due to wetter weather in the tropics, which in turn increased microbe activity in the wetlands, producing more of the gas. Added to this, other measuring stations near the Arctic circle were recording much higher methane readings. This was perhaps due to less ice covering the usually frozen northern pole, for a shorter period each year, he said.

However, human activities were also playing a definite role in the increasing amounts of the gas -- including increased commercial livestock farming, the mining of fossil fuels, urban gas network leaks and burn-offs from tropical rainforests, he said.