Canadian psychologist and culture war commentator Jordan Peterson says planet Earth has got 20% greener in the last 20 years. But satellite data tells a different story. We investigate the correct number, with the help of Dr Chi Chen, from Rutgers University in the US.Presenter: Kate Lamble Series producer: Tom Colls Production co-ordinator: Brenda Brown Sound mix: Giles Aspen Editor: Richard Fenton-Smith