Tiers of data are a way of describing the type and quality of data that has been used to calculate emissions. Tiers are based on the system used by the International Panel for Climate Change and referred to within the Global Protocol for Community-scale greenhouse gas emissions (GPC). The Tier of data increases as the data improves so Tier 1 is lower quality and Tier 3 is the highest quality.
The Tiers take into consideration two categories of data: activity data, and conversion factors. Activity data is a measurement of the activity that is generating emissions and is the primary mechanism for establishing emissions figures (the only alternative being to measure carbon emissions directly): for example km travelled by car. Conversion factors are the variables that are used to convert this activity data into emissions estimates.
There are three Tiers:
Example: Residential electricity emissions for Victorian municipalities are calculated by scaling state level energy consumption data to the municipal level based on the population, dwelling type and SEIFA rating of the municipality.
Example: Transport emissions for municipalities with Google EIE transport data are calculated based on actual journey distance travelled per year by each transport mode (car, train, bus, tram) and use national or state level emissions factors for fuel and electricity.
Example: For municipalities where there is a landfill site within the municipal boundary, and where data is available, emissions for Solid Waste could be calculated using site specific waste weights and emissions factors. This is not currently the case for Snapshot as this data is not consistently available.
At present, most sectors of emissions that are included within Snapshot are Tier 2. For an overview of data used for each sector and state please see the Snapshot Methodology 2022 which can be downloaded from the Resources page.