Estimating the uncertainty of methane emissions from New Zealand's ruminant animals

In New Zealand, the principal source of methane emissions to the atmosphere (ECH4ECH4) is ruminant animals, up to ca. 85 million sheep and cattle fed by year-round outdoor grazing on pasture. Uncertainty analysis is developed for a change in ECH4ECH4 from 1 year to another (ΔECH4ΔECH4). For 1990 and 2003, annual ECH4ECH4 averaged 1036 Gg and ΔECH4ΔECH4 was 88 ± 52 Gg with 95% certainty that ΔECH4>0ΔECH4>0 was due to a true increase of emissions. The standard error was largely attributed to uncertainty in estimating pasture herbage consumption from the animal's energy requirements for maintenance and production.