At its core, the CO2 argument is an energy balance argument and many of the details are unnecessary. To determine long-term, global temperature rise, you just need to know the energy in and energy out, which can be done in principle without knowing anything about climate.
The problem is that some things that affect the radiation balance, chiefly changes in water vapor and clouds, are products of the local conditions, and it is to estimate the effects of those that you need simulations.
The problem is that people seem to transfer their skepticism of the global climate simulations to the basic energy balance argument. Humans ARE affecting the climate, it's just that we may be affecting it in such a way that the net warming is hard to estimate because there are fairly large forcing terms that cancel.
The problem is that some things that affect the radiation balance, chiefly changes in water vapor and clouds, are products of the local conditions, and it is to estimate the effects of those that you need simulations.
The problem is that people seem to transfer their skepticism of the global climate simulations to the basic energy balance argument. Humans ARE affecting the climate, it's just that we may be affecting it in such a way that the net warming is hard to estimate because there are fairly large forcing terms that cancel.