Global carbon dioxide levels in the atmosphere surpassed 400 parts per million in March for the first time on record, federal researchers said.
The National Oceanic and Atmospheric Administration (NOAA) said Wednesday that the global average represents a new milestone in carbon dioxide concentrations from human activities like burning fossil fuels.
The 400-parts-per-million milestone first came to the Arctic in 2012 and to the NOAA’s Mauna Loa Observatory in Hawaii in 2013.
“It was only a matter of time that we would average 400 parts per million globally,” Pieter Tans, lead scientist of NOAA's Global Greenhouse Gas Reference Network, said in a statement, calling the level “a significant milestone.”
“This marks the fact that humans burning fossil fuels have caused global carbon dioxide concentrations to rise more than 120 parts per million since pre-industrial times," he said. “Half of that rise has occurred since 1980.”
Carbon dioxide is the most common greenhouse gas that is believed to warm the planet.
Some scientists and environmentalists have said in recent years that a global carbon level of 350 parts per million is the maximum level to prevent catastrophic global warming. Others put the threshold at 400 or 450 parts per million.
Researchers believe the last time global carbon exceeded 400 parts per million was during the Pliocene Epoch, 3 million to 5 million years ago.