sigh.....CO2 is logarithmic, after the first doubling, the effects are virtually negligible due to the increased radiance of the earth. In fact, you get about 70% of the warming out of the first 40% of doubling CO2. You would need close 1200 ppm of CO2 to generate 7.4 W/mm for another 1C in temperature which would take you about 500 years to reach.
Like I said, nothing to see here.