UPDATE (9.25am): The booths have now all been moved by security.
Over the past hour or so, impromptu ticket exchange booths have been appearing in airports across the UK.
Greenpeace volunteers (fetchingly dressed as stewards and stewardesses - pics here) have been offering BA passengers checking into domestic flights climate-friendly train tickets.
It's not just because we're generous souls - it's also because flying causes 10 times more damage to the climate than taking the train. And it's responsible for 13 per cent of the UK's impact on the climate (that's the government's own figures).
It's also the fastest growing source of emissions in the UK; between 1990 and 2050, emissions from aviation could quadruple, which scientists say could wipe out all other emissions savings we make in every other sector.
The main cause of this massive growth in the UK is the proliferation of short haul flights - often unnecessary domestic ones like the 30 or so a day between London and Manchester.
British Airways (despite its claims to be green) is one of the worst offenders, opening new and unnecessary domestic routes, fiercely opposing any measures that will curb growth in emissions, keeping a tight hold over government policy and lobbying hard for airport expansion.
You can find out more about aviation and climate change here.
And you can email BA's Chief Executive, Willie Walsh, asking him to ground unnecessary domestic UK flights on routes that are already well served by trains, and to end BA’s lobbying for more runways and bigger airports.