Version 2 (Current version)
The calculator assumes an emission rate of ¼ tonne CO2 per hour flying.
This is a composite figure derived from a number of sources.
Version 3 (Work in progress)
The calculator is currently (Jan 08) being revised to take into account further published sources.
The Quaker Green Action calculator [1] uses 0.35 tonnes CO2 per hour flying
There are several complexities in allocating responsibility for aviation greenhouse gas emissions.
One is the variation in passenger occupancy rates of aircraft, with some fully laden with charter passengers, and others flying with less than half the seats occupied (which applies more to scheduled flights). Those flying in partly empty aircraft should perhaps allow a higher rate of CO2 emissions. Similarly those flying business class or first class are responsible for a higher share of CO2 emissions.
These points are related to the fallacy of "the plane is taking off anyway". Some people argue that because a plane is flying anyway, it makes no difference to the CO2 released whether or not they are on it (since their added weight is insignificant). And so (they argue) they will continue flying and make no effort to cut back. But what this ignores is that the decision made by an airline to start up flights on a particular route and to continue them (and to increase or decrease their frequency) depends upon the revenues received by the airline. So it not the travelling on the aircraft that causes the CO2 emisions, but buying a ticket which encourages the airline to persist with the route and so release greenhouse gases - and the more money someone pays the airline, the more likely it is to continue or even increase its flights on a particular route. One consequence of this line of argument is that those buying high-priced peak tickets are more responsible for the planes flying than those buying cheap off-peak seats - and this effect can be by at least a factor of 10 since seat prices can vary by this much. Carbon calculators could perhaps incorporate this but the practical difficulties would be hard to overcome. But people who are finding it hard to cut back on flying, can take the intermediate action of avoiding the peak-time highly-priced seats where the airlines are getting their largest income and making their greatest profits.
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