Use of Models and Facility-Level Data in Greenhouse Gas Inventories

Use of Models and Facility-Level Data in Greenhouse Gas Inventories
averaging as was previously applied in the 1996 IPCC Guidelines, or where appropriate models are available, provide a
contrast model with the sources of variability excised, so as to determine the scale of variability.
The use of models to identify the scale of influence of externalities on emissions estimates has been considered
previously by an IPCC expert workshop as a method to factor out the non-anthropogenic effects on emissions. The
meeting ‘Revisiting the use of managed land as a proxy for estimating national anthropogenic emissions and removals’
(Brazil, May 2009) considered the use of Tier 3 models to provide a comparison of two time-series of emissions
estimates, with and without human activities included.
In this way, there are many similarities between decisions on the treatment of non-anthropogenic emissions in natural
disturbances and extreme events, and the treatment of inter-annual variability, much of which may be non-anthropogenic.
Conclusions
The IPCC 2006 Guidelines provide strong guidance on the desirability of national inventories having the “...best
approximation of real emissions/removals, and a time series of single year estimates..... Countries should, where
possible, avoid using multi-year averaging of data.....” Though pointing to cases for exception, this clarifies the
desirability of both estimating and reporting actual emissions on an annual basis thereby including reflection of interannual
variability as an estimation and reporting goal.
Though it is preferable to reflect year-to-year variability in making and reporting emissions estimates, this does create an
accounting problem. When accounting considers short periods, e.g., several years, the pattern of inter-annual variability
over that period could distort the outcome so as to mask a longer term trend. In this case the accounting creates a policy
problem as the pattern of inter-annual variability is a form of a non-exceptional force majeure, a routine but largely
unpredictable variability, mostly but not entirely beyond human control. Just as how to treat emissions from natural
disturbances on managed lands has raised accounting and policy questions, so does the consideration of nonanthropogenic
components of inter-annual variability.
IPCC Expert Meeting Report 38 TFI