Here goes, it is an argument that cannot scientifically ever be proven. Yes you can measure temperature and you can run models and those models might be spot on, but they might not be because you don't have a control earth etc to compare  them to. So to absolutely prove this with good scientific methods beyond a doubt you would need three earths in a laboratory  and maybe 10,000 years of data.  Barring that, this argument will forever remain a theory and it will evolve. If it is really beyond doubt then anybody researching the cause and effect of man on climate should immediately give up their research money and go work on some other problem.  If the global warming alarmist would at least admit that models are not  proven science, I think they might actually get more support and then we could talk openly about the likelihood of the models being right , instead of having it shoved down our throats as a done deal.