Carbon dioxide concentration in atmosphere hits new high, wa

The concentration of carbon dioxide (CO2) in the atmosphere averaged a record 400 parts per million in 2015, an ominous milestone for the planet's health, the UN said Monday. 

The greenhouse gas has previously passed the 400 ppm threshold on certain months in specific locations but never on an annual global basis, the United Nations World Meteorological Organization said. 

In its latest Greenhouse Gas Bulletin, WMO also reported that CO2 concentration rates had "surged again to new records in 2016" and predicted the annual average would stay above 400 ppm "for many generations."