The environmental effects of aviation in the United Kingdom are increasing due to the increasing demand for air travel in the country. In the past 25 years the UK air transport industry has seen sustained growth, and the demand for passenger air travel in particular is forecast to increase more than twofold, to 465 million passengers, by 2030. Two airports; London Heathrow and London Gatwick, are amongst the top ten busiest airports in the world for international passenger traffic. Whilst more than half of all passengers travelling by air in the UK currently travel via the five London area airports, regional airports have experienced the most growth in recent years, due to the success of 'no-frills' airlines over the last decade.