Claim: "This March, for the first time in human history, the monthly average carbon dioxide in our atmosphere exceeded 400 parts per million. The range had been 170-300 parts per million for hundreds of thousands of years."
Fact-check: Sen. Whitehouse gets it right: CO2 in air at historic levels
Verdict: true
Organisation: PolitiFact
Author: Mark Reynolds
Date published: 2015-06-21T00:00:00