President Donald Trump has used Twitter to mock Greta Thunberg, the 16-year-old Swedish campaigner who has urged world leaders to combat climate change.

Greta, who sailed across the Atlantic in a yacht to attend the event, scolded the audience at the UN Climate Action Summit on Monday, repeatedly asking: “How dare you?”

Greta said: “We are in the beginning of a mass extinction and yet all you can talk about is money. You are failing us.”

In a tweet, Mr Trump said: “She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!”

Mr Trump had spent only a few minutes at the climate summit, a centrepiece of this year’s UN general assembly schedule.