Not many people understand climate change. But they can recognise hypocrisy when they see it...
On Tuesday, Prince Charles flew to Copenhagen to attend the climate change summit, where he delivered a keynote speech. He informed his audience that 'the world has only seven years before we lose the levers of control'.
If we have so little time, and man-made climate change is such a terrifyingly imminent threat, he might have taken a boat or train to Copenhagen, or even, as a symbolic gesture, decided to walk. But he commandeered a jet belonging to the Queen's Flight, generating an estimated 6.4tons of carbon dioxide, 5.2tons more than if he had used a commercial flight.
Meanwhile his fellow prophet of doom, Gordon Brown, was making his own way to Copenhagen the same day.
This is the man who proclaimed in October that we had '50 days to save the world'. Before leaving he conjured up on a television programme the certainty of 'floods and droughts' with 'climate change evacuees and refugees' if agreement is not reached in Copenhagen.
Mr Brown chartered a 185-seat Airbus to take him and 20 aides to Denmark. Was a smaller plane producing less carbon dioxide not available?
Could he perhaps have shared an aircraft with Prince Charles? Might he have considered taking a scheduled flight to the Danish capital, of which there were 16 on Tuesday?
And, yes, I intended the the play on words.