Bad idea: Growing Gatwick

If ever there was a bad week to start talking again about extra airport runways - and not just at Heathrow, but Gatwick, too - surely this was it. On the day that the UN climate-change summit opened in Copenhagen, the House of Commons transport committee published a report backing a third runway at the world's second-busiest airport, and suggesting that consideration be given to a second one at Gatwick. After all, it argued, "in these difficult economic times" (a phrase that turns up at least twice) aviation is an industry we should be making the most of.

To be fair, the report isn't exactly a rallying call to aviatory arms (wings?). The committee just pointed out that, with plans for a second Stansted runway on hold, and unlikely to go anywhere before the current restrictions on building at Gatwick are lifted in 2019, Crawley's most famous landmark might be a better choice.

While that may be true, there are one or two other factors to take into account. For one thing, as the report notes, expanding airports in the south-east won't do much for the rest of the UK without major investment in rail links and the like. And, for another, air travel accounts for roughly 6 per cent of the UK's carbon emissions, which amounted to 564 million tonnes in 2007. We are already committed to cutting that figure by more than a third by 2020, and by the end of the summit the required drop may be as hefty as 42 per cent.

According to a 2007 report by the Tyndall Centre (including, yes, scientists at the University of East Anglia - see Mark Lynas's column), Britain's carbon dioxide emissions from aircraft doubled between 1990 and 2000. And as the transport committee notes, passenger demand is expected to double by 2030. The UK would have to stop all other carbon dioxide emissions to allow aviation to expand this fast, and still meet our targets.

But limiting flights is a Luddite response, we are told. Greener fuels and cleaner planes will save us from having to choose between cheap flights and keeping Lincolnshire above sea level. Which is brilliant news, except that, so far, the technology has not materialised. When government research found that expanding Heathrow would breach pollution targets, the solution wasn't to increase funding for new technology; the Department for Transport just "reforecast" its predictions, using more amenable figures supplied by BAA.

Surely it would be wise, before planning airport expansion, to work out whether we really are headed for an airy future of clean-power flights. Failing that, it would at least make cynical good sense to leave the discussion for a week less dominated by plans to save the world.