much you need invest to have those emissions reduced somewhere else. So, if you simply want to know what will be the emissions from a specifi c flight or household operation, they will be quite helpful. The Tufts Climate Institute recommended four companies and their calculators: Myclimate, Climate Friendly, Native Energy and Atmosfair.

The latter is appreciated for estimating emissions from flying which is quite a complex procedure. Factors a good calculator takes into account for flying include the type of ticket (economy passengers generate lower emissions than business or first class ones, because they account for less weight per unit of fuel burnt for each passenger), model of plane (more modern aircraft are more fuel-efficient), occupancy rate (the fewer empty seats there are, the less wasteful empty space is being flown around the world) and the flight distance (a substantial share of the GHG emissions generated from a flight occur during take-off and landing, so longer distance flights are more GHG efficient per unit of distance, and non-stop flights are more GHG efficient than indirect flights). Even if you might not be able to account for this in your calculations, be aware that the total warming effect of your flight is higher than just what is attributed to CO2 emissions directly. There are other emissions from aviation apart from CO2, such as nitrogen oxides and water vapour, and CO2 emitted at high altitude has an enhanced warming effect.

Varying outcomes
Whichever climate calculator you decide to use, you need to remember that there are sometimes huge variations between their conclusions – not surprising when you remember that they often start from quite different assumptions. One calculator, for example, estimated the emissions from a return flight
from a European capital to Tokyo at 15.66 tonnes, another at 1.71 tonnes.

Find your own
Before choosing one particular calculator as being best suited to your needs, it is probably worth trying several and comparing their results. Do they explain, in terms you can understand, how they reach their conclusions? What factors does the calculator include, and what does it omit: food, leisure, consumption, transportation? Are the questions the calculator asks you detailed enough to produce useful and honest results, rather than just relying on your rose-tinted view of your own behaviour to give you the answers it thinks you want, not the ones you need?

64 KICK THE HABIT THE CYCLE – COUNT AND ANALYSE