The UK government asked the wrong question. It demanded that the Committee on Climate Change calculated how much air travel can rise without causing an increase in aviation emissions. Not unsurprisingly, the CCC answered by saying that the number of trips could rise at the same rate as efficiency improvements in air travel. The Committee said that emissions per passenger will fall by about 1% a year, and so travel could rise by about this amount. No shocks there.
By 2050, the CCC opined, the number of passengers taking trips from UK airports can rise to 370 million a year, up from 230 million today. The maximum possible number of new passengers at Heathrow from the addition of new runway and sixth terminal is about 60 million. Hoorah, said the industry, there's space for the expansion. Unsurprisingly, the press misinterpreted the Committee's report and said that it had 'approved' the government's plans for the airport. By answering the government's disiningenous question, the CCC has lost some of its impartiality.
The Department for Transport played a blinder. It could have cautiously asked the CCC whether Heathrow expansion posed a threat to the UK's climate target of an 80% emissions reduction. Or were the costs to cut emissions more rapidly in other sectors greater than the benefits from aviation expansion? Then the Committee could have pondered and said that since Heathrow growth will add about 1.5% to the UK's emissions, it definitely doesn’t make achieving the targets any easier. But no, the DfT didn’t give the CCC this option. It simply required the CCC to do a bit of arithmetic:
Maximum air travel increase allowed = (rate of airframe / engine improvement X rate of replacement of planes) + air traffic control improvements + (rate of biofuels introduction X carbon intensity saving) + improvements in load factors.
Perhaps the CCC resented the limited brief. It actually made some quite conservative assumptions about each of the elements in this equation, pushing the government's figures down as far as it could. Nevertheless, if you simply want to hold the UK's emissions from aviation bunker fuel down to the current level of 37.5m tonnes, a new runway at Heathrow is clearly possible.
Rate of airframe / engine improvement The CCC considered that annual improvements in fleet efficiency would be about 0.7% a year. This is slightly lower than the industry projects. The next generation of airplanes will be perhaps 25% more efficient per passenger kilometre than the average plane retiring from the UK fleet. At the current rate of aviation growth and the typical length of life of passenger airplanes, this may mean about a 1% yearly improvement in fleet efficiency.
Over the 40 years to 2050, this apparently small difference compounds into a big gap. 0.7% means a 32% improvement over the 40 years to 2050. 1% means a 49% increase.
The chief scientist of the CCC's sponsoring government department, Energy and Climate Change, said in his book, 'No redesign of a plane is going to radically improve its efficiency. A 10% improvement? Yes, possible. A doubling of efficiency? I'd eat my complimentary socks.' The CCC agrees with his physics-based view even as the aviation industry pressure groups pretend that much larger improvements are possible.
Air traffic control and other operational improvements The industry says that Heathrow congestion causes emissions by forcing planes to stack over south-east London waiting to land. This is undoubtedly true but curing this will be far from simple. The CCC has taken a cautious view of what is possible. Sensibly enough, it has concluded that adding 60% to the traffic by 2050 is likely to act as a brake on any major improvements in air traffic routing. It has projected improvement of about 0.1% a year.
Biofuels The airline industry airily talks of making flying carbon neutral ('net zero' in North American language) by using biofuels. The CCC took a much more conservative view, saying that the limited amount of agricultural land around the world could not be devoted to producing jatropha oil for aviation. It said that only 10% of the fuel would come from biofuels by 2050 and this kerosene would have a net carbon cost of 50% of fossil fuels.
The net effect of these changes and load factor improvements is to increase 'efficiency' (passenger distances per litre of fuel burnt) by about 60% by 2050. Hence Heathrow expansion is possible without breaching the artificial cap set by the government of not exceeding today's emissions levels.
The implications for aviation's share of emissions Implicitly the government is suggesting that other sectors need to decarbonise faster as a result of aviation's emissions remaining constant. Perhaps this is the right analysis – it probably is more difficult to decarbonise aviation than other sectors of the economy. But the implication of the UK decision is that other fossil fuel uses will have to cut their emissions even more rapidly than expected.
At the moment, the CO2 from aviation's share of emissions is somewhat over 5%. The UK intends to reduce its emissions by about a factor of five over the next 50 years. So if air travel emissions are unchanged they will rise to over 25% of total emissions by 2050. (The CCC points out that restraining air travel growth to a 60% increase will require a) a £200 per tonne carbon tax; b) a shift to some videoconferencing and greater use of rail; and c) capacity constraints at many airports and even still 60% is a tight target.) This means that the rest of the economy will have to cut emissions even faster than otherwise. The space for non-aviation emissions will decline by about 85%.
It is even worse if we consider the non-CO2 effects of aviation. These include contrails and other global warming effects not related to carbon dioxide. The CCC suggests, in line with current scientific opinion, that current evidence suggests that these impacts approximately double the effect of jet aircraft. Include these effects, therefore, and aviation uses up 50% of the whole UK carbon budget in 2050. The CCC very deliberately refers to this problem but the uncertainty over the exact impact means that it doesn’t include these effects in its assessment. If the UK government decides at some stage to load aviation with a multiplier of 2 for non-CO2 effects – as is increasingly likely – the percentage rate of annual reduction in other sectors will have to be even faster than if the CCC had decided to do so today. And yet the CCC has repeatedly said that to achieve the required cut in other sectors is already hugely demanding. Giving aviation an easy ride has just made it worse.
Herein lies the problem. The UK government wanted the CCC to 'approve' its plans to expand Heathrow. Its remit allowed the CCC no discretion to say no to the advantages given to aviation even though the cost this expansion imposes on other sectors is high. Nowhere in the CCC's report is any assessment of the higher cost to decarbonise other sectors resulting from the freedom given to aviation by the government's prescriptions. We do not, for example, know the financial impact of the tighter targets for other activities such as transport, home heating or power generation. It may be that the economic and social benefit of allowing aviation to expand is very great and therefore the favouritism shown to the flying is justified. But the Committee has not been allowed to make this calculation. It has been obliged to fulfil the role of the arithmetician to the government and not its policy adviser. One has to say that this is a waste of some of the best brains in Britain.
Footnotes  More detail on this assumption is provided at here in an earlier Carbon Commentary article on "Heathrow expansion" (Monday 26 November 2007), but I'm using the implied CCC figures here.  David J. C. MacKay, Sustainable Energy – Without the Hot Air. [ad#Amazon MacKay for sidebar]