A source inventory for atmospheric methane in New Zealand and its global perspective

Methane is an important greenhouse constituent of the atmosphere. Its global source inventory is briefly reviewed, and the aggregated source in the range 270–760 Tg CH 4 /yr is compatible with independent measurement. The constraints imposed by isotopic information are also discussed. We then exploit this global data base to provide a first detailed estimate of New Zealand sources of methane and their uncertainties, placing these in global perspective. The aggregate New Zealand methane source is estimated to lie in the range 1.3 –2.2 Tg/yr. Nearly all of this emission is caused by human modification of the environment and is dominated ( ∼75%) by “enterically fermented” methane from farmed livestock, predominantly by sheep and lambs (58%) and by cattle (40%). At about 0.3% of global emissions, New Zealand is a disproportionately large methane source on either a per capita or land area basis, or when compared with the New Zealand share (0.13%) of global carbon dioxide emissions from industry and from fossil fuel consumption.