claim: Doubling the concentration of atmospheric CO2 from its pre-industrial level, in the absence of other forcings and feedbacks, would likely cause a warming of ~0.3A°C to 1.1A°C
evidence: The global temperature increase since the beginning of the industrial period ( taken as 1750 ) is about 0.8 °C ( 1.4 °F ), and the radiative forcing due to CO 2 and other long-lived greenhouse gases – mainly methane, nitrous oxide, and chlorofluorocarbons – emitted since that time is about 2.6 W / m2.