An overseas report stating that global methane emissions from agriculture are larger than estimated previously does not call into question the accuracy of New Zealand’s greenhouse gas measurements, say the leaders of the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC).
The report, published in the journal ‘Carbon Balance and Management’, has estimated that global livestock methane emissions for 2011 were 11 percent higher than estimates based on default emission factors for national emission inventories provided by the Intergovernmental Panel on Climate Change (IPCC) in 2006. It attributes the discrepancy to changes in livestock productivity (for example milk yield, bodyweight, liveweight gain) that have occurred since the IPCC guidelines were published. These increases in animal productivity mean higher feed intakes and hence higher methane production.
The authors of the report did remark that there was notable variability in trends in estimated emissions, and that results will differ from locally derived estimates.
Dr Harry Clark, the Director of the NZAGRC, says New Zealand’s greenhouse gas measurement methodology is rigorous, and the report’s findings do not apply to the situation here.
“This report is a global analysis using a simple methodology. New Zealand has one of the most detailed inventories in the world and already takes into account the factors incorporated into this new study,” Dr Clark says. “Any estimates based on fixed emission factors, wherever they come from, will always be wrong over time. New Zealand updates its inventory on an annual basis and hence this study says nothing about the accuracy of New Zealand’s emissions estimates which are derived in a far more sophisticated way.”
The NZAGRC’s Deputy Director (International), Dr Andy Reisinger, says as farm animals become more productive around the world, it is to be expected that emissions per head of livestock will also rise.
“The adjustment proposed by this study is only an issue for countries that rely on default values for their emissions per animal—and defaults are, by definition, only an approximation and almost never correct for a specific circumstance,” he says. “The productivity of livestock systems around the world keeps increasing—that’s a good thing from the perspective of food security and resource efficiency, but it does mean that emissions per animal are also expected to increase. This study simply confirms this expectation, but the numbers it provides will become out of date again ten years from now.”
Dr Clark says the report’s findings demonstrate the importance of the work New Zealand is doing to help improve the way greenhouse gas emissions are estimated around the world.
“A major effort is underway internationally to get countries to develop improved greenhouse gas accounting methods that move away from fixed values. As part of its contribution to the Global Research Alliance New Zealand—through the work of staff at the NZAGRC and MPI—is leading a specific initiative in Southeast Asia to assist countries to implement more comprehensive and up-to-date agricultural greenhouse gas accounting methods,” says Dr Clark. “All countries now have to provide biennial updates of their greenhouse gas emissions and hopefully this will result in more accurate and continuous updating of agricultural emissions.”