Boise Weekly: 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...