Government emissions reduction targets currently exclude international aviation emissions as there is no agreed way of allocating responsibility for these to individual countries.
However under the current proposal to include aviation in the EU ETS, emissions from the aviation sector would be capped at the level of average 2004-06 emissions, and carbon allowances would only be issued up to the level of this cap. Emissions over this cap will be covered either through mitigation within the sector or through the purchase of reductions that can be produced more cheaply and easily by other sectors. This would be the case regardless of whether this growth in emissions was from new airport capacity, the provision of new routes or extra services on existing routes. This approach means that growth in aviation (including Heathrow expansion) would be sustainable.