Then the
expression for the expected CO2 concentration in 2010 reads -LRB-[CO2] in 2010) = 280 + (368 - 280) * exp -LSB-(10/100) * ln -LRB-[836 - 280] / [368 - 280]-RRB--RSB-, which gives a value of 386 ppm for 2010, so in fact the
rise in CO2
levels that we have seen is a bit above what is expected for the A2 scenario if we assume that the amount above the 280ppm background is increasing exponentially
to a total concentration of 836ppm in 2100 and that this total concentration had the value of 368ppm in 2000.