ClimateWire: Global CO2 levels rose above 400 parts per million for the first time ever in the modern era in March 2015, marking a significant milestone in the planet's progression toward a warmer future. The measurements were released by the National Oceanic and Atmospheric Administration.
The last time CO2 levels were this high was 3 million years ago during the Pliocene era. There was little ice at the poles then. Ellesmere Island, which is today part of the Canadian tundra, had forests growing on it. ...