For about 10 000 years before the industrial revolution, the atmospheric abundance of CO2 was nearly constant at ~ 280 ppm (ppm = number of molecules of the gas per million molecules of dry air). This level represented a balance among the atmosphere, the oceans and the biosphere.
Since 1750, atmospheric CO2 has increased by 38%, primarily because of emissions from combustion of fossil fuels (8.7Gt carbon in 2008, http:// www.globalcarbonproject.org/), deforestation and land- use change.
High-precision measurements of atmospheric CO2 beginning in 1958 show that the average increase in CO2 in the atmosphere (airborne fraction) corresponds to ~55% of the CO2 emitted by fossil fuel combustion. The remaining ~45% has been removed from the atmosphere by the oceans and the terrestrial biosphere. The airborne fraction of CO2 varies inter annually, without a confirmed global trend.
Globally averaged CO2 in 2010 was 389.0 ppm and the increase from the previous year was 2.3 ppm (Figure 3). This growth rate is higher than the average for the 1990s (~1.5 ppm/yr) and the average for the past decade (~2.0 ppm/yr).