In another ominous sign of human-caused climate change, US government scientists said Wednesday that global carbon dioxide concentrations have reached a new monthly record of 400 parts per million.
Carbon dioxide is a potent greenhouse gas, and is a harmful by-product of burning fossil fuels such as oil and coal.
"For the first time since we began tracking carbon dioxide in the global atmosphere, the monthly global average concentration of this greenhouse gas surpassed 400 parts per million in March 2015," said the National Oceanic and Atmospheric Administration (NOAA).
Scientists announced that C02 had passed the 400 ppm level for the first time in the Arctic in 2012.
"It was only a matter of time that we would average 400 parts per million globally," said Pieter Tans, lead scientist of NOAA's Global Greenhouse Gas Reference Network.
"Reaching 400 parts per million as a global average is a significant milestone."
Tans said C02 has risen more than 120 parts per million since pre-industrial times.
"Half of that rise has occurred since 1980," he said.
