If Khan was opposed to enabling more take-offs and landings at Heathrow because of the increasing contribution aircraft emissions are making to climate change, he would be opposing the expansion of Gatwick too.
Congratulations to Sadiq Khan. His selection adds another interesting candidate to the race to be London's next Mayor.
The Green Party candidate Sian Berry has a worthy opponent in Khan, the man who infamously led Labour's anti-Green 'attack unit' during the recent General Election campaign.
The selection of Sadiq Khan as Labour's candidate is welcome in one particular respect: it helps to maintain the principle that no-one can be elected Mayor of London if they support the expansion of Heathrow airport.
Ken Livingstone and Boris Johnson established that principle between them, but Tessa Jowell would have broken it - and would therefore have had a hard time against the likely Tory candidate, Zac Goldsmith, who is vociferously opposed to the airport's expansion.
This may make a difference to the final result of the Mayoral election, because voters' second preferences count. If the Greens come third then their voters' substantial number of second preferences will be redistributed. Tessa Jowell would have had very little credibility for this part of the electorate.
Heathrow no, Gatwick yes - too bad about the climate
However the situation with Sadiq Khan is more complex. He opposes the expansion of Heathrow - but favours expanding London's other big airport at Gatwick. According to an Evening Standard report, Khan says he has "thought long and hard" about what they describe as the "aviation capacity crisis".
He stressed he was "not anti-aviation" and is in support of a new runway being built to expand Gatwick. Of course the Standard often misrepresents people and gets things wrong. But on the same date Khan himself wrote an article for City AM in which he said:
"I believe the answer to the airport capacity problem lies in expanding Gatwick and making Heathrow better, not bigger."
Khan may have thought long and hard about airport capacity, but has he given any thought at all to dangerous human-triggered climate-change?
There are many reasons for opposing Heathrow expansion, including noise, air pollution, road traffic congestion, and the destruction of housing. Khan shows every sign of taking those arguments seriously.
But if he was also opposed to enabling more take-offs and landings at Heathrow because of the increasing contribution aircraft emissions are making to climate change, he would be opposing the expansion of Gatwick too.
The only intellectually consistent position from which to champion airport expansion is the systematic denial of climate science. There is no sign that Khan takes this view. Therefore, his opposition to Heathrow expansion runs the risk of being in the end nothing more than NIMBY-ism.
Who is the greenest of them all?
For the sake of building cross-party co-operation against the Tory Government, it would be good if Green voters felt they could give a Labour candidate their second preferences. But what will Sadiq Khan do to earn them?
Without standing firm against London airports expansion full stop, as Greens stand firm, it's as yet hard to say. And, given that Khan is likely to be up against the renowned green-leaning Zac Goldsmith - a former editor of The Ecologist - he will have his work cut out.
However even Goldsmith - whose opposition to Heathrow expansion is a key platform of his campaign for the mayoralty - is curiously silent on the bigger issues.
In a thundering editorial in the Evening Standard last May, for example, he lambasted Heathrow expansion citing air pollution, traffic congestion and BAA's monopolistic tendencies, but had nothing to say on either climate change or whether Gatwick expansion would be acceptable.
The reality is that, as we lean into this mayoral election race in London, the only thing that Greens can say with one clear voice is: vote Green. Vote for our superb candidate, Sian Berry.
If Corbyn can come from being a complete outsider to being the hot favourite to win the Labour leadership, then surely it can be time too for Londoners to get behind the only candidate who can be trusted to stand firm against any more crowding of our skies - and pollution of our atmosphere.
Let the Green momentum build ...
Event: Sian Berry will be speaking on this issue in London today, Saturday 12th September. Bloomsbury Central Baptist Church, 235 Shaftesbury Ave, London WC2H 8EP starting 2pm.
With: Keith Taylor, Green Party MEP, Prof Alice Bows-Larkin, Tyndall Centre, Manchester University; Christine Taylor, Stop Heathrow Expansion; Brendon Sewill, Gatwick Area Conservation Campaign; Leo Murray, A Free Ride; Dr Doug Parr, Greenpeace; Asad Rehman, Friends of the Earth; Sian Berry, Green London Mayoral Candidate; Cllr Jonathan Essex South East Greens; John Stewart HACAN.
Victor Anderson is a former Green Party Member of the London Assembly. Rupert Read is the Green Party's national Transport Spokesperson. Both are core members of Green House.