The United Nations recently predicted that the world's population will grow to nine billion by 2050 and ten billion by the end of the century.

Whilst news of population growth is often greeted with panic and dismay Danny Doring, a human geographer at the Oxford University Centre for the Environment, argues that, in fact, there's nothing to fear in the future, because the population bomb has already diffused.

Four Thought is a series of talks which combine new ideas and personal stories.

Recorded during the Edinburgh festival, speakers explain their thinking on the trends and ideas in culture and society in front of a live audience.

Producer: Caitlin Smith.