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). Meanwhile, negotiations have been slowly proceeding in the International Civil Aviation Organisation (ICAO) on the development of a global emissions scheme for aviation. At the end of 2012, these negotiations came to a standstill.
The EU therefore conceded to 'stop the clock' for one year on all international flights in the EU ETS, in order to allow ICAO to make real progress on the global emissions scheme. 'Stop the clock' means that only intra-EU flights are regulated under the ETS. 'Stop the clock' was supposed to be a temporary solution until global progress was made at ICAO. However, the ICAO Assembly decision in October of 2013 was merely to “develop” a scheme for international aviation emissions, without any definitive commitment. The EU Commission has since then proposed to continue 'stop the clock' until 2017 anyway, to give ICAO even more time. In April 2014 the European Parliament voted to accept 'stop the clock' till 2017. This is an environmentally ineffective and unsustainable regulation of aviation emissions. Read more about why here.