What is the RFI, and how is it used?

Known gross emissions from aircraft are multiplied by an RFI to give a more representative figure. There are two components to consider here:

• Firstly, we have radiative forcing, which involves the balance between the sun’s radiation reaching the earth, and heat leaving the earth from anthropogenic and natural factors.
• Secondly, greenhouse gases emitted at altitude result in more potential heating than if the same amount was emitted at sea level, as higher altitudes affect fuel combustion and emission characteristics.

Accounting for the interaction between these phenomena at altitude requires accurate measurement methods. This is where the RFI comes in.

Often an RFI is only applied if the flight reaches high altitude (25,000 feet or 7.6km). For example, if a plane was on an 800 km flight and its altitude was above 25,000 feet for 250km, the RFI would only be applied to 250km of the flight.

Estimations for the RFI from different literature range from 1.0 to 3.0. However, there is no consistent recommendation on which RFI value should be used. In its programmes, Toitū Envirocare takes a conservative approach and applies an RFI of 1.9 to the entire flight journey. This approach is informed by our current understanding of the science, published literature and international best practice.