Methane increasing over New Zealand

Levels of the climate warming methane gas have begun to rise again in the Southern Hemisphere as measured at Wellington's Baring Head, Niwa says.

NIWA said atmospheric methane increased by 0.7 percent over the two-year period 2007-08, a change it called globally significant news.

That is about 35 times more than all the methane produced by New Zealand livestock each year, the statement said.

"This is significant in that it follows a three-year period of no growth, and accounts for more than half of the growth observed over the ten years 1999-2008 (1.2 percent)."

Methane is the second most important contributor to global warming behind carbon dioxide, though its abundance in the atmosphere is far lower.

"The evidence we have shows that methane in the atmosphere is now more than double what it ever was during the 800,000 years before 1700AD" says NIWA Principal Scientist, Dr Keith Lassey.

The trends observed by NIWA at Baring Head are consistent with global trends.

It is the global atmospheric concentration of greenhouse gases that determines the risk of climate change.

The US National Oceanic and Atmospheric Administration (NOAA) reported that global methane concentrations rose in both 2007 and 2008 after a ten-year lull.

NOAA reported that drier than normal conditions in the tropics from 1999-2006 probably limited emissions from microbes in tropical wetlands while from 2007 wetter tropics and warmer Arctic conditions have led to increased emissions overall.

The wetter tropics were at least partly a result of a La Nina weather pattern of 2007 and 2008.

Other factors are at work in increasing atmospheric methane levels: global growth in commercial livestock farming, mining of fossil fuels, leaks from urban gas networks, and continued burn-offs of tropical rainforest.

- © Fairfax NZ News