Tourism is also one of the greatest environmental threats, above all due to the impact of air travel. Aviation accounts for 75% of the industry’s greenhouse gas emissions, followed by road transport (32%) and accommodation (21%)]. In 2006 378 million tourists a year (45% of the total) travelled by air, the most polluting form of transport per passenger-kilometre, and with a 4-5% increase each year it is the fastest growing source of greenhouse gas emissions. If current trends continue, by 2030 the carbon emissions from aviation alone will exceed the nation’s total carbon allocation under a 450 ppm regime. Increasingly, tourists are taking longer flights than most business travellers. What’s more, these emissions are released directly into the upper atmosphere where they cause far more damage, and more rapidly, than if released at ground level. Thus, taking the train to Paris instead of flying effectively cuts CO2 emissions by 90%. Given how hellish airports are these days this is an increasingly popular option.