Methane and nitrous oxide are New Zealand’s main non-carbon dioxide greenhouse gases. Methane comes mainly from the belching of ruminant animals, and nitrous oxide emissions come from animal excreta and nitrogen fertilisers. In 1990 methane emissions from livestock totalled about 20 million tonnes (non-agricultural sources of methane include the energy sector and landfills, which make up much of the remaining 5 million tonnes). By 2001 this had increased by nearly 10%, mainly due to the increase in dairy cow numbers. Emissions from sheep had declined due to a drop in numbers.