Climate scientists say the level of the greenhouse gas methane in the southern hemisphere atmosphere has risen for the first time in three years.
Measurements at NIWA's Baring Head station, near Wellington, show that atmospheric methane in the southern hemisphere increased by 0.7% over 2007 and 2008, after a three-year period of no growth.
The principal scientist at NIWA, Keith Lassey, says the rise may be due to natural sources of methane reverting to their usual levels; dry conditions in the tropics between 1999 and 2006 led to less methane being emitted from wetlands.
Apart from the period of no growth, however, Dr Lassey says there's been an upward trend of methane emissions in the past few decades, largely because of human activities such as livestock farming and coal, gas and rice production.
He says the latest rise, which reflects global trends, is equivalent to about 35 times all the methane produced by New Zealand livestock each year.