Blue and Green: For the first time in at least 800,000 years, the average level of carbon dioxide in Earths atmosphere exceeded 400 parts per million (ppm) for a full month in April.
Measurements made at a National Oceanic and Atmospheric Administration (NOAA) observatory in Hawaii showed that the monthly average in April reached 401.33ppm.
The Scripps Institution of Oceanography at the University of California which runs the observatory -- says it is the first time in human history that levels of the greenhouse...