In this report the Commissioner examines the issue of agricultural greenhouse gases – methane and nitrous oxide – which together form about half of New Zealand’s greenhouse gas emissions. This high proportion of emissions coming from agriculture is a major challenge for New Zealand. The science is complex and the policy debate is polarised. 

The sheep, cattle, deer, and goats – the ruminants – on our farms burp out a huge amount of methane. And the origin of most of the nitrous oxide – an especially powerful greenhouse gas – is the urine of farm animals.
This report is about the science of these two biological gases – how they are formed, how they behave in the atmosphere, and what might be done about them.

The main policy ‘instrument’ in New Zealand for reducing greenhouse gas emissions is the Emissions Trading Scheme (ETS). The biological gases from agriculture have not yet been included in the ETS. Some argue they should be; others make the opposite case. 

This particular dispute, however, lies within a bigger question – what, if anything, should we do about the methane and nitrous oxide from agriculture? Our efforts to answer this question will be more efficient and constructive if we have a common understanding of the basic science. It is hoped that this report will help develop that understanding.