As the aviation industry is usually keen to point out, planes account for only around 1.5%–2% of global CO2 emissions. However, this figure is somewhat misleading. For one thing, most flights are taken by the wealthy, so in developed countries the slice of CO2 emissions caused by flying is higher – around 6.3% in the UK, according to Department for Transport figures for 2005. Even this figure underplays aviation’s environmental footprint, however, and not just because the number of flights has risen since 2005. There are at least three other reasons why 6.3% is likely to be a strong underestimate.