The average level of CO2 in the atmosphere for the first time topped 400 parts per million for a full month, according to the Scripps Institution of Oceanography at UC San Diego.
Last May, the Mauna Loa Observatory in Hawaii for the first time measured carbon dioxide at greater than 400 parts per million, averaged over one day. C02 exceeded 400 parts per million two months earlier this year than last year, according to researchers at NOAA.
But now we've hit an unwelcome milestone, with every day in April averaging more than 400 parts per million.
It's likely this record-breaking moment marks the first time in 800,000 years that the Earth's atmosphere contained this much CO2.
"We continue to turn the dial up on this ‘electric blanket' of ours without knowing what the resulting temperatures will be," said James Butler, director of the Global Monitoring Division of NOAA's Boulder-based Earth System Research Laboratory (ESRL), in a statement released Friday.
NOAA also released its Annual Greenhouse Gas Index (AGGI), Friday, which showed carbon dioxide levels, measured at 80 sites around the world, increased 1.5 percent between 2012 and 2013 -- and 34 percent since 1990.
"We know that the world is getting warmer on average because of our continued emissions of heat-trapping gases," Butler said. "Turning down the dial on this heating will become increasingly more difficult as concentrations of the long-lived greenhouse gases continue to rise each year."