Carbon dioxide levels in the atmosphere have broken through a symbolic mark.
Daily measurements of CO2 at a US government agency lab on Hawaii have topped 400 parts per million for the first time...
The last time CO2 was regularly above 400ppm was three to five million years ago - before modern humans existed.
Scientists say the climate back then was also considerably warmer than it is today.
Carbon dioxide is regarded as the most important of the manmade greenhouse gases blamed for raising the temperature on the planet over recent decades.