The world passes 400ppm carbon dioxide threshold. Permanently
We are now living in a 400ppm world with levels unlikely to drop below the symbolic milestone in our lifetimes, say scientists.
Brian Kahn for Climate Central, part of the Guardian Environment Network
Wednesday 28 September 2016 10.00 BST
In the centuries to come, history books will likely look back on September 2016 as a major milestone for the world’s climate. At a time when atmospheric carbon dioxide is usually at its minimum, the monthly value failed to drop below 400 parts per million (ppm).
That all but ensures that 2016 will be the year that carbon dioxide officially passed the symbolic 400 ppm mark, never to return below it in our lifetimes, according to scientists.