four million years a level not seen since since the Pliocene Climate Milestone: Earth's CO2 Level Nears 400 ppm has details Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm National Geographics 400 parts per million Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm article in National Geographic National Geographic 400 part per million (ppm) Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth’s CO2 Level Nears 400 ppm 400 ppm "Climate Milestone: Earth’s CO2 Level Passes 400 ppm" first time since Climate Milestone: Earth's CO2 Level Nears 400 ppm since the Pliocene Epoch "Climate Milestone: Earth’s CO2 Level Passes 400 ppm" http://news.nationalgeographic.com/news/energ... Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm National Geographic Climate Milestone: Earthâs CO2 Level Passes 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm "Climate Milestone: Earth’s CO2 Level Passes 400 ppm" Climate Milestone: Earth’s CO2 Level Passes 400 ppm 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm excellent story Climate Milestone: Earth’s CO2 Level Passes 400 ppm 400 parts per million (ppm) Climate Milestone: Earth's CO2 Level Nears 400 ppm "Climate Milestone: Earth’s CO2 Level Passes 400 ppm" excellent story National Geographics 400 ppm in May of 2013 Climate Milestone: Earth’s CO2 Level Nears 400 ppm four million years recently measured at 400 parts per million Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Pliocene era four million years National Geographic was last this high Climate Milestone: Earthâs CO2 Level Passes 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm SOURCE Climate Milestone: Earth's CO2 Level Nears 400 ppm http://news.nationalgeographic.com/news/energ... 400 parts per million Climate Milestone: Earth's CO2 Level Surpasses 400 ppm 400 ppm briefly passed 400 ppm greater than 400 parts per million as of spring 2013 “Climate Milestone: Earth’s CO2 Level Passes 400 ppm” turned a corner on climate change four million years Robert Kunzig, National Geographic four million years 400 ppm Climate Milestone: Earthâs CO2 Level Passes 400 ppm “Climate Milestone: Earth’s CO2 Level Passes 400 ppm” National Geographic, May 9, 2013 Climate Milestone: Earthâs CO2 Level Passes 400 ppm 3 million Dostupné online. 400 parts per million (ppm) Climate Milestone: Earth's CO2 Level Nears 400 ppm National Geographic "Climate Milestone: Earth’s CO2 Level Passes 400 ppm" National Geographics 400 parts per million National Geographics hasn’t been seen in 3 million years Climate Milestone: Earth's CO2 Level Nears 400 ppm reported Climate Milestone: Earth's CO2 Level Nears 400 ppm growing "Climate Milestone: Earth’s CO2 Level Passes 400 ppm" "Climate Milestone: Earth’s CO2 Level Passes 400 ppm" 400 parts per million Climate Milestone: Earth’s CO2 Level Nears 400 ppm recently measured at 400 parts per million recently measured at 400 parts per million National Geographics Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm 400 part per million (ppm) Climate Milestone: Earthâs CO2 Level Passes 400 ppm 400 part per million (ppm) Climate Milestone: Earth's CO2 Level Surpasses 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth’s CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm four million years Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm Climate Milestone: Earth's CO2 Level Surpasses 400 ppm Climate Milestone: Earth's CO2 Level Nears 400 ppm