World in 'new danger zone' – climate chief
The world has entered a "new danger zone" with levels of Earth-warming carbon dioxide in the atmosphere never experienced by humankind, the UN's climate chief has warned.
The United States, China and India are the world's biggest emitters of CO2.
When it breached the CO2 threshold of 400 parts per million last week, the world "crossed an historic threshold and entered a new danger zone," Christiana Figueres said in a statement urging policy action.
The level measured by US monitors has not existed on Earth in three to five million years – a time when temperatures were several degrees warmer and the sea level was 20 to 40 metres higher than today, experts said.