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2. Emission factors and methods – context

The emission factors reported in this publication are intended to be default factors (ie, to be used in the absence of better information). They are designed to be consistent with the reporting requirements of ISO 14064-1 and The GHG Protocol. The emission factors are also designed to be aligned with the emissions factors used for the Ministry’s national greenhouse gas inventory reporting.

The purpose of providing these emission factors is to:

  • collate an official set of emission factors for voluntary corporate reporting

  • present emission factors in an ‘easy to use’ form which will facilitate reporting by corporate organisations

  • provide emission factors for some emission sources which were not previously publicly available (eg, waste to landfill, taxis)

  • provide guidance on a consistent approach to choosing emission factors for financial year and calendar-year reporting.

As discussed previously, these emission factors are largely derived from technical information published by New Zealand government agencies.4 The key source of the emission factors contained in this publication is the Ministry of Economic Development’s Energy Greenhouse Gas Emissions 1990–2006 publication (Ministry of Economic Development, 2007). Information is also taken from the Ministry of Economic Development’s New Zealand Energy Data File publication (Ministry of Economic Development, 2007) and the Ministry for the Environment’s New Zealand’s Greenhouse Gas Inventory (Ministry for the Environment, 2007). The relevant sources for each emission factor and how the emission factors are derived are discussed in more detail below.

This guidance covers the six direct Kyoto gases (CO2, CH 4, N2O, HFCs, PFCs and SF6) covered by ISO 14064-1 and The GHG Protocol.5 This is also consistent with the reporting requirements for New Zealand’s Greenhouse Gas Inventory.

Greenhouse gases (GHGs) vary in their radiative activity and atmospheric residence time. This means that different GHGs have different global warming potentials (GWPs). To enable a meaningful comparison between gases, GHG emissions are commonly expressed as carbon dioxide equivalent or CO2-e. The emission factors in this publication therefore convert activity data into the equivalent estimate of CO2-e per unit of activity data (eg, kg CO2-e/litre of petrol). They have been converted to CO2-e using GWPs sourced from the Energy Greenhouse Gas Emissions publication.6

Under the reporting requirements of ISO 14064-1 and The GHG Protocol, GHG emissions should be reported in tonnes CO2-e. This guidance presents emission factors in kg CO2-e per unit. Division by 1000 converts kg to tonnes (see example calculations below).

In line with the reporting requirements of ISO 14064-1, the emission factors provided allow calculation of CO2, CH 4 and N2O separately (as well as the total CO2-equivalent) for Scope 1 (the concept of “scope” is discussed below in Section 2.2) emission sources. Emission factors for CH 4 and N2O are expressed in kg CO2-e.

CO2 emissions factors are derived based on the carbon content and energy content (ie, calorific value or heating value) of a fuel. CO2 emissions (for a specific fuel) therefore remain constant regardless of the way in which a fuel is combusted. However CH 4 and N2O (ie, non-CO2) emissions depend on the manner in which the fuel is being combusted. The emission factors for CH 4 and N2O therefore vary depending on the combustion process.7 Separate CO2-e emission factors for commercial and industrial users are presented in Table 1. The Energy Greenhouse Gas Emissions publication discusses the source of the relevant emission factors in more detail. Any assumptions which are made in the underlying reports are also made for these emission factors.

As well as providing common emission factors, the Ministry considers it useful to illustrate how these emission factors have been derived. Appendix 1 discusses (and shows an example) of how the emission factors have been calculated.

2.1 Timing of emission factors and annual reporting

Organisations should report on a calendar-year basis where possible.

Calendar year: If you are reporting on a calendar-year basis then you should wait until the emission factors for the reporting period become available in the following year (for example the 2007 emission factors will be published in 2008). Many factors will rely on a review of historical data, such as the proportion of renewable generation feeding into the electricity grid. The previous calendar year’s emission factors will therefore be provided in this publication each year, following the release of the Energy Greenhouse Gas Emissions, New Zealand Energy Data File and New Zealand’s Greenhouse Gas Inventory publications.

Financial year: If you are reporting on a financial year-basis then you should pro rata the emission factors according to the specific financial year used by your organisation. For example, if you wished to report on your 2006/2007 emissions then you would need to wait until the Ministry issued this publication in 2008, in order that the 2007 emission factors (as well as the 2006 emission factors) were available.

Organisations could choose to adopt the policy of using the emission factors contained in the most recent report. This is likely to be less accurate than using data determined specifically for the reporting year, and is not the preferred approach.8

2.2 The concept of “scope”

The GHG Protocol categorises emission sources into Scope 1, Scope 2 and Scope 3 activities as follows:

Scope 1: Direct GHG emissions occur from sources that are owned or controlled by the company (ie, sources within the organisational boundary), for example emissions from combustion of fuel in owned or controlled vehicles. The GHG Protocol and ISO 14064-1 require Scope 1 emissions to be reported.

Scope 2: Electricity indirect GHG emissions occur from the generation of purchased electricity9 consumed by the company. The GHG Protocol and ISO 14064-1 require Scope 2 emissions to be reported.

Scope 3: Other indirect GHG emissions occur as a consequence of the activities of the company, but occur from sources not owned or controlled by the company, for example emissions from air travel. Under the reporting framework of The GHG Protocol and ISO 14064-1, Scope 3 is an optional reporting category that allows for the treatment of all other indirect emissions.

Section 3 of this publication presents emission factors according to each category of activity.

4 For instance the energy emission factors are largely sourced from the Energy Greenhouse Gas Emissions publication. References for specific emission factors are included below.

5 HFCs, PFCs and SF6 are gases commonly used as refrigerants and are therefore not associated with the combustion of fuels.

6 Appendix 1 contains a table of the GWPs used in these conversions.

7 For example the CH 4 and N2O emission factors for diesel used for industrial heating are different to the CH 4 and N2O emission factors for diesel used in vehicles.

8 This will be particularly so in the case of emissions from purchased electricity, which vary significantly from year to year, depending on the proportion of generation from renewable sources.

9 The term electricity is used by The GHG Protocol as shorthand for electricity, heat, or steam. Purchased heat and steam are also Scope 2 emissions.