Global atmospheric CO2 concentration has surpassed 400 parts per million (ppm) in the atmosphere of Mauna Loa, Hawaii for the first time since measurements began more than five decades ago.

The Mauna Loa Observatory under the U.S. government’s Earth System Research Laboratory said Friday carbon dioxide in the area's atmosphere recorded 400-point-03 ppm on Thursday afternoon.

Readings from Mauna Loa are considered global references as the observatory is the oldest CO2 observatory in the world.

Atmospheric CO2 concentration has steadily risen since the observatory started taking measurements in 1958.