On March 12, 2014, NOAA MLO recorded the first daily average above 400 ppm since Spring 2013.
Atmospheric CO2 for March 2014
Preliminary monthly average as of April 2, 2014
(Mauna Loa Observatory: Scripps CO2 Program)
NOTE: On May 10, 2013, NOAA & Scripps first reported daily averages that temporarily reached 400 ppm.