US economist Jeffrey Sachs
Media playback is unsupported on your device
Video

UN adviser Jeffrey Sachs on 'alarming climate change'

A UN climate change summit is taking place in New York which aims to galvanise 120 member states to sign up to a new global climate agreement at talks in Paris next year.

The US economist Jeffrey Sachs is a special adviser to Ban Ki-moon and he is also director of The Earth Institute at Columbia University.

The BBC's Michelle Fleury started by asking for his reaction to Sunday's demonstration in New York calling for action on climate change.

Go to next video: Global push to tackle climate change