
Globally averaged concentration of carbon dioxide in the atmosphere reached the symbolic and significant milestone of 400 parts per million for the first time in 2015 and surged again to new records in 2016 on the back of the very powerful El NiƱo event, according to the World Meteorological Organization's annual Greenhouse Gas Bulletin.
CO2 levels had previously reached the 400 ppm barrier for certain months of the year and in certain locations but never before on a global average basis for the entire year. The longest-established greenhouse gas monitoring station at Mauna Loa, Hawaii, predicts that CO2 concentrations will stay above 400 ppm for the whole of 2016 and not dip below that level for many generations.

