Dr Steven Barrett from Massachusetts Institute of Technology explains more about the findings of his report and how he came to his conclusions:
More top news
Amnesty International say up to 100 000 people turned out for the Women's March on London anti Trump protest
A man in his 20s is dead and a 17 year girl has hand injuries after a stabbing in Tooting
Roads were closed in Barnet after a water main burst on Graham Park Way causing flooding and low water pressure.