When international aviation and shipping were left out of the 2008 UK Climate Change Act, this caused concern. Would cuts elsewhere be cancelled out by increasing emissions from these sectors - the equivalent of our carbon bloated economy going on a diet, but one in which all calories are counted (except those from chocolate and cake)?
The Committee on Climate Change, set up under the Act, had a solution. They set a 'planning assumption' - a limit they recommended the government keep aviation emissions below - of 37.5Mt carbon a year. The committee sets gradually shrinking carbon budgets for other sectors of the economy to allow for this level of emissions from aviation. So the overall aim of the Act - to reduce UK emissions by 80% by 2050 - can be achieved in a meaningful way.
It is difficult to reduce emissions from flying, since it's inherently energy intensive. Recognising this, aviation was therefore given a generous allowance, limiting emissions at 2005 levels, rather than the dramatic cuts expected from other sectors.
But from the government's support for a third runway at Heathrow airport, and their current consultation on aviation strategy which focuses on growth, it appears they have no intention of keeping to these limits. The idea is that increasing emissions from a growing aviation industry can be dealt with internationally, freeing us from any obligation to attempt to limit emissions here. Unfortunately these solutions have about as much credibility as the click-bait diet ideas that pop up on the internet: "This one weird tip" which produces amazing weight loss. They seem too good to be true - and they are.