The world has entered a "new danger zone" with a record level of Earth-warming carbon dioxide in the atmosphere, UN climate chief Christiana Figueres said today.
With a CO2 level of 400 parts per million (ppm) announced last week, the highest in human history, the world "crossed an historic threshold and entered a new danger zone," she said in a statement urging policy action.
The level measured by US monitors has not been seen in three to five million years -- a time when Earth's temperatures were several degrees Celsius warmer and the sea level was 20 to 40 meters (22 to 44 yards) higher than today, experts say.
The 400 ppm threshold had been expected to be breached for some time, but campaigners say it should nevertheless serve as a wake-up call in efforts to curb greenhouse gas emissions through fossil fuel use.
"The world must wake up and take note of what this means for human security, human welfare and economic development," said Figueres.
"In the face of clear and present danger, we need a policy response which truly rises to the challenge.
