Inventory practice: Uncertainty analysis to prioritize further research in New Zealand

Sadie S

Keywords: Uncertainty analysis | meta-analysis | statistical analysis

What data needs were addressed? To understand the contribution of key factors to inventory uncertainty and provide an improved estimate of overall uncertainty of the livestock inventory.

Why was the data needed? In 2008, the estimated uncertainty in the national enteric methane (CH4) emission inventory was ±53%, which was far greater than the estimate for other similar countries. Previous uncertainty analysis conducted in the early 2000’s had identified that uncertainty in the quantity of CH4 produced per unit of feed consumed had a significant impact on overall uncertainty estimates. Since the early 2000’s, the number of related measurement studies had greatly increased and a larger pool of data was available to reassess the related uncertainty.

Methods used: meta-analysis of research data, analysis of statistical uncertainty.

How was the data need addressed?

  1. Meta-analysis of experimental measurements using the SF6 method and caliometry showed that the mean methane yields were similar between sheep of different ages (<1 year and >1 year) and between sheep and cattle.
  2. Analysis of the coefficient of variation in methane yield enabled a revised estimate of uncertainty in the overall livestock enteric methane inventory, which was estimated at ±16%.
  3. Analysis of uncertainty in the methane yield measurement data suggested that in order to reduce uncertainty of the methane yield parameter from 3% to 2%, an additional 400 measurements from 5 experiments would be required, but uncertainty of the overall enteric fermentation inventory would only reduce by 1%.
  4. Analysis of data on methane yield and feed intake as a proportion of energy requirements suggested that methane yield may be inversely proportional to the level of feed intake. The study concluded that further research on this topic is required, because if this relationship is established, then the method used in the inventory to estimate methane yield may need revision.

Resources

Kelliher FM, Clark H, Smith MH, Lassey KR, Sedcole R. 2009. Reducing uncertainty of the enteric methane emissions inventory. A report prepared for the New Zealand Ministry of Agriculture and Forestry, Wellington.