World crosses 400ppm threshold for carbon dioxide

According to scientists, September is the month when atmospheric levels of Co2 should be at their lowest. The level for the month is above 400 parts per million (ppm) which means 2016 is on track to be the year that we officially pass the 400ppm threshold, which is seen as hugely symbolic and important.

The last time CO2 levels were this high, humans did not exist.

Read more at the Guardian website.