Can somebody explain the joke?

Emma Thompson and assorted taxpayer-funded luvvies were out in force yesterday to launch "Green Screen London", an initiative to cut "CO₂ emissions by film-makers".

Alistair McGowan, referrred to as a comedian, said "As we live in a make-believe world, it's easy to forget that our CO₂ footprint is real".

I dunno, was this an inversion of the rather more correct statement "Even though we live in the real world, it's easy to forget that our CO₂ footprint is make-believe" or was his joke more subtle than that?