While the difference in emissions output should not differ significantly from one calculator to another, there are a few reasons as to why this may happen. Some calculators may use different criteria to calculate emissions. Variations in individual behavioural estimates, conversion factors, and accounting for radiative forcing and uplift factors can also affect the carbon emissions output.

Another reason may be that some calculators could be out-of-date, since emissions factors are updated every year.

We recommend that you only use calculators that:

  • provide sources for emissions factors
  • use radiative forcing and account for an uplift factor

We work to ensure that the emissions factors in our calculator are up-to-date, such that we can provide you with the most accurate and detailed representation of your carbon footprint. The emissions factors that we have used for the calculator are:

The IPCC’S “Aviation and the Global Atmosphere” report recommends that a radiative forcing factor being included, and the UK Government recommends that an uplift factor also be used when calculating flight emissions. Condensation trails (contrails) may also impact these calculations.

What is radiative forcing?

The IPCC defines Radiative forcing (RF) as “a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system and is an index of the importance of the factor as a potential climate change mechanism…radiative forcing values are for changes relative to preindustrial conditions defined at 1750 and are expressed in Watts per square meter (W/m2).”

The IPCC has also indicated that the location of emissions from aircraft is a further driver for climate change, “Aircraft emit gases and particles directly into the upper troposphere and lower stratosphere where they have an impact on atmospheric composition. These gases and particles alter the concentration of atmospheric greenhouse gases, including carbon dioxide (CO2), ozone (O3), and methane (CH4); trigger the formation of condensation trails (contrails); and may increase cirrus cloudiness—all of which contribute to climate change.”


What is an uplift factor?

The uplift factor adds 8% to emissions based on distance flown, due to aircraft stacking (circling), and the fact that some routes are not direct (e.g., due to weather conditions, or flying around international airspace).

How do contrails impact emissions?

During flight, airplanes’ engines produce condensation trails (contrails) from their exhaust, putting out a thermal blanket of linear clouds made up of ice particles. While they only last in the atmosphere for a short time, they have a direct impact on climate change.

No, they are not. Carbon offsets are not charitable donations; they are a purchase to mitigate greenhouse gas emissions. They help with the transition to a low carbon economy by creating a financial incentive for companies/people to create emissions reductions that would not happen otherwise.
No, they do not. Carbon offsets are considered a financial instrument/purchase and are therefore taxed normally, so there is no tax-deductible on them.

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