In their annual greenhouse gas bulletin, the World Meteorological Organization (WMO) says there is no sign of reversal in this rising trend.

Carbon dioxide levels reached 405 parts per million (ppm) in 2017, a level not seen in 3-5 million years.

Researchers also note the resurgence of a banned gas called CFC-11.
Concentrations differ from emissions in that they represent what remains in the atmosphere after some of the gases are absorbed by the seas, land and trees.

Since 1990 the warming impact of these long lived gases on the climate has increased by 41%.

2017 continues the rise in concentrations of CO2 which are now 146% greater than the levels in the atmosphere before the industrial revolution.

The increase from 2016 to 2017 was smaller than the rise from 2015 to 2016, but is close to the average growth rate seen over the last decade.

The scientists at the WMO believe that the amount of CO2 in the atmosphere right now hasn't been seen in a long, long time.

"The last time the Earth experienced a comparable concentration of CO2 was 3-5 million years ago, when the temperature was 2-3C warmer and sea level was 10-20 metres higher than now," said WMO Secretary-General Petteri Taalas.

BBC