CO2 now comparable to levels seen 4 million years ago: NOAA

How the World Passed a Carbon Threshold and Why It Matters - Yale E360

CO2 Now at Levels Unseen in 3.6 Million Years - In These Times

CO2 Science

Earth's CO2 Home Page

Carbon dioxide has hit a level not seen in four million years. This is what it means for the world

CO2 Past

Do high levels of CO2 in the past contradict the warming effect of CO2?

Earth's Atmosphere Passes Significant Carbon Milestone - Dan's Wild Wild Science Journal - AGU Blogosphere

Carbon dioxide hits highest sustained rate ever recorded as greenhouse gases creep toward uncharted levels, NOAA says - CBS News

400 ppm World, Part 1: Large Changes Still to Come – State of the Planet

NOAA Climate.Gov - Teaching Climate? This animated visualization represents a time history of atmospheric carbon dioxide in parts per million (ppm) from 1979 to 2016, and then back in time to 800,000

Climate Change: Atmospheric Carbon Dioxide

World News: Get all Latest Breaking Global News Stories, Photos & Videos

Earth May Be 140 Years Away From Carbon Levels Not Seen In 56 million Years - SpaceRef