The 2012 average annual concentration of CO2 in the atmosphere (Mauna Loa Observatory) is 393.84 parts per million (ppm). The 2011 average is 391.65 ppm.
For the past decade (2003-2012) the average annual increase is 2.1 ppm per year. The average for the prior decade (1993-2002) is 1.7 ppm per year. Annual data for 2012 was first posted January 3, 2013, by the Scripps Institution of Oceanography in the United States.
Since the 1958 start of precision CO2 measurements in the atmosphere, the annual mean concentration of CO2 has only increased from one year to the next. The CO2 data below provide a simple view of the annual trend.
Year CO2 (ppm) Notes
2009 387.35 Copenhagen Accord
1997 363.76 Kyoto Protocol
1992 356.37 Earth Summit in Rio de Janeiro
1987 348.93 The last year when the annual CO2 level was less than 350 ppm
1959 315.98 The first year with a full year of instrument data
Source Annual CO2 Data: Scripps Institution of Oceanography: CO2 Program
Annual and monthly data for atmospheric CO2 | 1958 - present | MLO / Scripps & NOAA
Accelerating rise of atmospheric CO2
Seasonal fluctuation in atmospheric CO2
Monthly data for atmospheric CO2