Results published this week by NOAA indicate that the monthly global average concentration of CO2 surpassed 400 parts per million in March 2015—the first time since recordkeeping began in 1959 that the monthly average has exceeded that level worldwide.
Above: This graph shows the rise of monthly average carbon dioxide concentrations from 2011 to March 2015 | Credit: NOAA
Said Pieter Tans, lead scientist of NOAA’s Global Greenhouse Gas Reference Network, in a statement:
It was only a matter of time that we would average 400 parts per million globally... We first reported 400 ppm when all of our Arctic sites reached that value in the spring of 2012. In 2013 the record at NOAA’s Mauna Loa Observatory first crossed the 400 ppm threshold. Reaching 400 parts per million as a global average is a significant milestone.
This marks the fact that humans burning fossil fuels have caused global carbon dioxide concentrations to rise more than 120 parts per million since pre-industrial times... Half of that rise has occurred since 1980.
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