Since 1960, the atmospheric concentration of carbon dioxide has risen from 310 to 390 parts per million.

CNN: What if carbon dioxide were as black as oil?

This measures the amount of warming that can eventually be expected to follow a doubling in the atmospheric concentration of carbon dioxide.

ECONOMIST: Climate change: Good news at last? | The

For the first time, scientists measured an average concentration of atmospheric carbon dioxide of 400 parts per million in Mauna Loa, Hawaii, where the National Oceanic and Atmospheric Administration observatory is located, on Thursday.

CNN: CO2 levels hit new peak at key observatory