The World Meteorological Organization (WMO) has officially announced that carbon dioxide levels in the atmosphere reached 407.8 parts per million in 2018 – an increase from the already record-breaking level of 405.5 parts per million (ppm) in 2017.

CO2 levels crossed the 400 ppm benchmark in 2015 and has continued to increase unimpeded. The rise in 2017 to 2018 is close to the increase seen between 2016 and 2017, and is slightly higher than the average yearly increase over the last decade, according to the Greenhouse Gas Bulletin.

“There is no sign of a slowdown, let alone a decline, in greenhouse gases concentration in the atmosphere despite all the commitments under the Paris Agreement on Climate Change,” WMO Secretary-General Petteri Taalas said in a statement. “We need to translate the commitments into action and increase the level of ambition for the sake of the future welfare of the mankind. [sic]”

It is not just carbon dioxide. Nitrous oxide and methane have also increased dramatically. As a greenhouse gas, methane is around 25 times more potent at trapping heat in the atmosphere than carbon dioxide. This phenomenon, known as radiative forcing, is the difference between the sunlight absorbed by the Earth and the energy radiated back into space. There has been a 43 percent increase in the total radiative forcing by greenhouse gases since 1990. Carbon dioxide alone is responsible for about 80 percent of this increase, according to the National Oceanic and Atmospheric Administration.

“It is worth recalling that the last time the Earth experienced a comparable concentration of CO2 was 3-5 million years ago. Back then, the temperature was 2-3°C warmer, sea level was 10-20 meters higher than now,” added Mr Taalas.

Global emissions will continue to rise without drastic measures to curb them. Models for today's current strategies suggest that carbon dioxide will not peak for another two decades at least.

The Greenhouse Gas Bulletin is produced annually to document the atmospheric concentrations of greenhouse gases entering the atmosphere, as well as the planet's geological and biological ecosystems. Half of greenhouse gas emissions do not stay in the atmosphere but are equally absorbed between the ocean and the biosphere.