what is an emission factor and why is there a reference date with it

A conversion factor from consumption to CO2 emissions

An emission factor is a fixed number used to convert consumption into a quantity of greenhouse gas. A litre of diesel, a cubic metre of gas or a kilowatt-hour of electricity does not by itself equate to kilograms of CO2 — the emission factor is the multiplier that produces that result. Without this number, there is only a list of consumption data from the energy bill or fuel receipts; with the emission factor, the emissions derived from it are calculated, which are requested in a sustainability report, usually broken down into scope 1, 2 and 3 as explained in the difference between scope 1, scope 2 and scope 3 is explained.

The reference date is included because emission factors themselves are not permanent. They are revised periodically — a kilowatt-hour of electricity from a year with high wind energy has a different factor than a kilowatt-hour from a year with more gas-fired power plants, and measurement methods are also refined. An emission factor without a reference date is therefore a number without an expiration date: it is unclear whether it is the most recent determination or an older one. When building a file, the factor used and its reference date are therefore recorded, so that the basis of a calculation can be traced afterwards.

Where this follows from the framework

The breakdown into scope 1, 2 and 3 comes from the GHG Protocol, the international framework that underpins the way greenhouse gas emissions are classified and calculated worldwide. The VSME standard of EFRAG builds on this for the basic module used by non-listed SME enterprises, and refers to this type of conversion factor for emission calculations. Because emission factors are revised on a regular basis, a reference date must be attached to every figure calculated with them — this is also why a change in an emission factor can have implications for an already-built file, as described in what to do if a change in the standard affects your own file.