Amount of carbon dioxide in air keeps rising, hits milestone -

Amount of carbon dioxide in air keeps rising, hits milestone,
May 6, 2015,
By Seth Borenstein, Associated Press,
OnlineAthens,

Global levels of carbon dioxide, the most prevalent heat-trapping gas, have passed a daunting milestone, federal scientists say.

The National Oceanic and Atmospheric Administration says in March, the global monthly average for carbon dioxide hit 400.83 parts per million. That is the first month in modern records that the entire globe broke 400 ppm, reaching levels that haven't been seen in about 2 million years.