Global carbon dioxide (CO2) concentrations have reached a new monthly record of 400 parts per million, according to scientists.
The milestone was announced by the US National Oceanic and Atmospheric Administration (Noaa).
They said it was the first month that the entire globe broke 400ppm, reaching levels that haven’t been seen for about two million years.
Noaa’s Pieter Tans said that reaching the mark was “a significant milestone”.
CO2 is a greenhouse gas meaning it traps heat in the planets atmosphere, that contributes to warming trends and global climate change. It would only take about 1000ppm of CO2 to completely melt the polar ice caps.
Scientists announced that CO2 had passed the 400 ppm level for the first time in the Arctic in 2012, and then at Mauna Loa in Hawaii in 2013.
“It was only a matter of time that we would average 400 parts per million globally,” said Mr Tans, lead scientist at Noaa’s Global Greenhouse Gas Reference Network.
He added that CO2 has risen more than 120 parts per million since pre-industrial times which is just under 300 years.
“Half of that rise has occurred since 1980,” he said.
Noaa collects its data on global carbon dioxide concentration on air samples taken from 40 sites around the world, including some remote islands.