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 ~0.3°C to 1.1°C.
evidence: Further evidence for environmental change around the P–Tr boundary suggests an 8 °C ( 14 °F ) rise in temperature, and an increase in CO 2 levels by 2000 ppm ( for comparison, the concentration immediately before the industrial revolution was 280 ppm, and the amount today is about 410 ppm ).