If, as expected, this lunchtime sees political approval for the expansion of Heathrow Airport, there will be some serious political fall out – including the resignation of MP Zac Goldsmith. Much of the debate will be over local environmental issues – noise, air quality – but the carbon argument has been largely confined to green circles.

Basically, as this excellent piece by Carbon Brief from last year points out, expanding either Heathrow or Gatwick will take us over the aviation carbon ‘budget’ for 2050 (which should be capped at 2005 levels to meet our requirements for an 80% cut). When Lord Deben wrote to Davies about this, the latter claimed that a combination of biofuels, a (steep) increase in carbon price and efficiencies should deliver those requirements. Carbon Brief raises some serious doubts about Davies’ assumptions.

Aviation is probably the hardest nut to crack in terms of techno-fixes. Biofuels are unlikely to provide sufficient quantities to make a dent without serious land use issues (unless there is a major breakthrough in, say, algae biofuel technology). Electric planes or nuclear planes have yet to make it past old episodes of Thunderbirds.

Policy changes are also difficult. I recall that over a decade ago, the PM’s own Conservative Party mooted a frequent flyer levy – you’d get one flight tax-free each year, after that you pay through the nose – but this perfectly reasonable solution was shot down in flames by The Telegraph and other right-wing papers. The average family at the time took 0.75 flights per year, so the papers’ argument that this would hit ordinary people’s holidays falls a bit flat, but they won anyway and the proposal was swiftly dropped.

The alternative to Heathrow is expansion of Gatwick. This is regarded as ‘less bad’ in terms of all environmental impacts, local and global, but only just.

There is of course another option: no expansion, anywhere. I’ve often said the litmus test for corporation’s sustainability commitments is not what they start doing but what they stop doing. So when B&Q refuses to stock patio-heaters on carbon grounds or Interface deletes product ranges with harmful chemicals, that’s true commitment. Putting a real constraint on aviation would be the most powerful incentive for low carbon alternatives.

So this is a litmus test for the May Government, and everybody expects them to flunk it. We may, of course, end up with ‘no expansion’ whatever decision is made today, if the process gets bogged down in years of protest, legal arguments and political wrangling. We shall see.

Photo: Konstantin Von Wedelstaedt – Gallery page http://www.airliners.net/photo//1572653/L