From 1 January 2012, emissions from all commercial flights arriving at or departing from EU airports have been subject to the EU Emissions Trading System (EU ETS). Aviation emissions were capped for the year 2012 at 97% of the sector’s emissions over the period 2004-2006 (212 million tonnes of CO2). Between 2013 and 2020, the cap will be set at 95% of aviation’s 2004-6 emissions. For 2012, airlines received 85% of their emissions permits for free, based on their 2004-6 level. From 2013 onwards they will receive 83% for free. Airlines that operate more flights (or operate less efficiently) than in 2004-6 will have to buy more permits.