##### GUIDE / Our Approach

# Estimating the carbon emissions of a flight.

We are working to build the most user-friendly flight emissions calculator on the web. Here is a bit of background on the math, the assumptions we've taken, plus some of the science of flight emissions.

# It's the miles that matter most.

If your goal is to come up with a highly precise calculation of the carbon-equivalent emissions of a flight, the math can get quite complex. Plane and engine size, occupancy rates, flight routes, fuel types, takeoffs and landings... these parameters all effect on the amount of fuel burned, and how much of that fuel you are responsible for.

What matters more than anything, however, is the distance you cover. In fact, while flying indeed emits about 30% more per mile than driving, it also takes you the furthest, the fastest. That's why it's so easy to ruin your carbon budget by flying!

# From Co2 to Co2e

Carbon dioxide alone is not harmful to us- it's the warming effects that are the problem. And since other gasses can cause a similar (or more powerful) warming effect, we use the term Co2-e, or "carbon equivalent" as a standard unit.

When we compare planes to cars and other forms of transportation, we use "grams of Co2e per passenger kilometer".

## Radiative Forcing

So what makes planes so much worse per kilometer? Aside from the amount of energy needed to move a plane a cross such distances, planes have an additional warming effects because they emit gasses much higher in the atmosphere, and because they emit more nitrous oxide. These additional warming effects are referred to as *radiative forcing effects*.

Collectively, the Co2e emissions of flying are typically calculated with a 2x "Emission Weighting Factor" to account for these effects.

# Result

Now that you know the above, you can understand how some simple multiplication (based on informed assumptions) can get us really close to an accurate number.

Our formula is quite simple:

- Calculate distance between airports, accounting for curvature of the Earth using the Haversine formula. Planes do not always fly in a perfectly direct path, but averaged over time this is a safe estimation.
- Multiply this by our average g/Co2/Pkm factor of 170.7
- Multiply this by our Emissions Weighting Factor (2) to account for Radiative Forcing and to be conservative with our estimations.
- Round the resulting kilograms of Co2e to the nearest tonne (the smallest standard offset unit!)

This is how we've made our calculator so easy to use, with only minimal sacrifice in accuracy. However, as the number and amount of flying increases, these inherent inaccuracies are amplified. For this reason we encourage you to contact us if you desire a more accurate and large scale emissions accounting!

We are continuing to test and improve our calculator, and would love to hear your feedback.

[1] Umweltbundesamt - Comparison of average emissions of modes of personal transport [2] Carbonbrief.org - Explainer: The challenge of tackling aviationâ€™s non-CO2 emissions