Data Sources and Methods for the National Greenhouse Gas Emissions Indicators
In general, greenhouse gas (GHG) emissions are estimated by multiplying activity data by emission factors.
Emissions = activity data × emission factor
Activity data refer to the quantitative amount of human activity resulting in emissions during a given time period. The annual activity data for fuel combustion sources, for example, are the total amounts of fuel burned.
Emission factors are based on samples of measurement data, and are representative rates of emissions for a given activity level under a given set of operating conditions. They are the estimated average emission rate of a given pollutant for a given source, relative to units of activity.
Guidelines produced by the Intergovernmental Panel on Climate Change (IPCC) for countries reporting to the United Nations Framework Convention on Climate Change (UNFCCC) provide various methods for calculating a GHG emission from a given human activity. The methods for estimating emissions are divided into “tiers,” each encompassing different levels of activity and technological detail. The same general structure is used for all tiers, while the level of detail at which the calculations are carried out can vary. Annexes 2 and 3 of the National Inventory Report (NIR) describe the methods used to estimate Canada’s GHG emissions, and illustrate that the selection of IPCC method type is highly dependent on the importance of each category and the availability of data.
The GHG emissions are reported in carbon dioxide equivalents (CO2eq), determined by multiplying the amount of emissions of a particular gas by the global warming potential (GWP) of that gas. GHGs differ in their ability to absorb heat in the atmosphere due to their differing chemical properties and atmospheric lifetimes. For example, over a period of 100 years, methane’s (CH4) potential to trap heat in the atmosphere is 21 times greater than carbon dioxide’s potential, and thus it is considered to have a GWP of 21. The IPCC publishes the GWPs and atmospheric lifetimes for each GHG which can be found in Table 1-1 of the NIR.
The GHG emissions by economic sector indicator represent a different classification than the activity sector emissions prescribed by the IPCC methodology. Instead of reporting on Canada’s emissions by activity, GHG emissions have been allocated to the economic sector in which they are generated (e.g., transportation emissions directly supporting an industrial activity, like off-road trucks in mining activities, have been allocated to the economic sector in which they are generated rather than to the transportation “activity” sector). A comprehensive detailing of the emissions reported by economic sector can be found in chapter 2 of the NIR.
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