The statement made by NIWA Principal Scientist, Dr Keith Lassey in a TV3 news story about methane (22 Dec 2009) is correct.
Dr Lassey said “Livestock globally account for about one-quarter of human-caused [methane] emissions. The rest of it’s shared between things like coal mining, oil and gas mining, rice, agriculture, burning rainforests.”
The numbers quoted for human-caused methane emissions are consistent with the Intergovernmental Panel on Climate Change (IPCC) report “Climate Change 2007: The Physical Science Basis” (The Fourth Assessment Report, 2007). We also note that livestock account globally for about 14% of natural and human-caused methane emissions combined.
NIWA’s measurements from its globally significant Baring Head station show that southern hemisphere atmospheric methane increased by 0.7% over the two-year period 2007–08. The increase is about 35 times more than all the methane produced by New Zealand livestock each year.
The trends observed by NIWA at Baring Head are consistent with global trends. However, it is not yet clear whether the recent rise can be attributed to human or natural causes, or a combination of both, though increased rainfall over tropical wetlands appears to have played a role.