# Carbon Offsetting & Air Travel Part 2: Non-CO2 Emissions Calculations

SEI Discussion Paper

**Author(s):**Kollmuss, A. ; Myers Crimmins, A.

**Year:**2009

This is the second of two papers that examine the key factors that have to be taken into account when calculating air travel emissions for the purpose of climate footprint and offset calculations. In order to estimate the full effect of aviation on climate, it is necessary to account for CO2 as well as for all other, non-CO2 warming and cooling effects. This paper is written for a non-technical audience and explains how to account for non-CO2 impacts of air travel emissions.

The non-CO2 warming effects of aviation are most commonly accounted for in emissions calculators through a Radiative Forcing Index (RFI) or a multiplier. These terms refer to a dimensionless factor which is multiplied by the calculated CO2 emissions in order to account for all warming effects. Our discussion shows the limitations to developing a dimensionless multiplier for the integration of non-CO2 effects into emissions calculators. Though science-based reasoning discourages the use of a simple multiplier to account for non-CO2 effects, such a multiplier is desirable from a policy and climate protection point of view. We elaborate on a number of scientific and value-related issues and conclude that a multiplier of 2 or greater should be used for air travel emissions calculators to account for non-CO2 warming effects.

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