claim: Given that a doubling of carbon dioxide would change the surface heat flux by only two watts per square meter, it is evident that a small change in cloud cover can strongly affect the response to carbon dioxide.
evidence: A typical value of λ, 0.8 K / ( W / m2 ), gives an increase in global temperature of about 1.6 K above the 1750 reference temperature due to the increase in CO 2 over that time ( 278 to 405 ppm, for a forcing of 2.0 W / m2 ), and predicts a further warming of 1.4 K above present temperatures if the CO 2 mixing ratio in the atmosphere were to become double its pre-industrial value; both of these calculations assume no other forcings.