Carbon dioxide levels in the atmosphere have surpassed a worrisome milestone for the first time in—brace yourself for this one—3 to 5 million years. Atmospheric CO2—one of the main man-made gases responsible for global warming—topped 400 parts per million, a symbolic marker that hasn't been seen since before modern human beings walked the earth.
The reading was taken Friday at the National Oceanic and Atmospheric Administration's Mauna Loa Observatory in Hawaii.
"It symbolizes that so far we have failed miserably in tackling this problem," Pieter Tans, the head of the monitoring program at NOAA told The New York Times.
Mauna Loa has been monitoring greenhouse gas levels since 1958, and has graphed the changes on what has become known as the Keeling Curve—named for scientist Charles Keeling—since then.
In 1958, Keeling found the concentration at the top of the volcano to be around 315 ppm (that is 315 molecules of CO2 for every 1 million molecules in the air). Every year since then, the Keeling Curve has inched resolutely higher.