make the argument explicitly. Here, I'll do it for you: doubling co2 levels should only lead to a 1c increase in temperature (~3w/m2 extra forcing).

That ignores all the other things that happen besides co2 forcing alone.

Your numbers most likely aren't exact. But most interesting is what you mean with "other things" and how much this is expressed in numbers. And have you looked up any numbers about methane?