Climate change scientists have warned the London Assembly that aviation capacity must not grow more than 60% from today's level by 2050, or else the UK will fall short of its carbon reduction targets.
On 16 October, Members of London's regional parliament questioned experts from the aviation industry, environmental researchers and local authorities about aircraft emissions and the UK government's pending aviation policy framework (APF). The government has issued a draft for review, but a final version will not be published until next spring.
Brian Hoskins, director of the Grantham Institute for Climate Change at London's Imperial College, says that net aviation carbon emissions are increasing despite improvements in fuel efficiency. While air traffic is growing at about 5% a year, he says that actual fuel consumption is falling around 2% - resulting in a net increase in emissions.
Hoskins says that aviation's share of the UK's total carbon emissions will grow from around 5% today to 25% in 2050 if the sector continues with "business as usual". Capacity growth should therefore be constrained, he argues. If passenger numbers grew by 60% until 2050, the UK could "just about meet" its carbon reduction targets.
Matt Gorman, director of corporate responsibility and environment at Heathrow - the airport operator formerly known as BAA, which is now using standalone brands for its individual hubs - says it should be possible to achieve "a bit more" than 60% passenger growth without exceeding the target.
But he concedes that other sectors are cutting carbon emission "significantly" and that aviation needs to go further than keeping its emissions stable.
Four years ago, the aviation industry pledged to improve fuel efficiency in the airline sector by 1.5% a year between 2010 and 2020, achieving carbon-neutral growth from 2020 and reducing emissions by 50% over 2005 levels by 2050.
Hoskins says that the 60% capacity limit is based on the assumption that the aviation industry will achieve "incredible" efficiency gains in technology and aircraft operation, as well as "some" biofuel employment and modal shift.