Uncertainty in Global Greenhouse Gas Emissions

There is considerable uncertainty about levels of greenhouse gas emissions particularly for those associated with land use change as well as for fugitive emissions associated with oil and gas extraction and coal mining. Estimates of emissions from the combustion of fossil fuels have the least degree of uncertainty, but do vary depending on the data source. In 2007 estimates of emissions from fossil fuel combustion varied by only 2.7% across data sources (Macknick, 2011). Default uncertainty estimates (2 standard deviations) that have been used by the IPCC for emissions coefficients for fossil fuel combustion range from 7.2% for coal use in industry to 1.5% for diesel used in road transport (Olivier et al., 2010). In summary, the uncertainty for fossil fuel based carbon dioxide emissions is ±5% (UNEP, 2012). There is much greater variation in estimates of carbon dioxide emissions from cement production and gas flaring but these are a relatively small fraction of total emissions (Macknick, 2011). Emissions from agriculture and land-use change are much more uncertain (Tubiello et al., 2013). It is estimated that carbon dioxide emissions associated with land use change have an uncertainty of ±50%. However, this means that total anthropogenic CO2 emissions have an uncertainty of only ±10% (UNEP, 2012).

Fugitive emissions of methane in fossil fuel extraction and supply are very uncertain. Between 2-4% of natural gas may be lost globally in transport and US estimates of fugitive methane emissions have an uncertainty of ±40% (Hayhoe et al., 2002). Estimates of N2O emissions are inherently uncertain (Olivier et al., 2010). Estimated uncertainties for global emissions of methane, nitrous oxide, and fluorine based gases are ±25%, ±30%, and ±20% respectively (UNEP, 2012).


References

Hayhoe, K., H. S. Kheshgi, A. K. Jain, and D. J. Wuebbles (2002) Substitution of natural gas for coal: Climatic effects of utility sector emissions, Climatic Change 54: 107–139.

Maknick, J. (2011) Energy and CO2 emission data uncertainties, Carbon Management 2(2): 189-205.

Olivier, J. et al. (2010) Application of the IPCC uncertainty methods to EDGAR 4.1 global greenhouse gas inventories, 3rd International Workshop on Uncertainty in Greenhouse Gas Inventories, Lviv.

Tubiello, F. N. et al. (2013) The FAOSTAT database of greenhouse gas emissions from agriculture, Environ. Res. Lett. 8: 015009.

UNEP (2012) The Emissions Gap Report 2012: A UNEP Synthesis Report, United Nations Environment Programme.