We cannot say if it is going to rain tomorrow in our town, so we really cannot expect to make accurate global weather simulations.
But we do know our chemistry well, we know the CO2 molecule very well and we seem to believe to understand a bit about planetary consequences of the greenhouse effect (it being that our neighbor Venus is a prime example). Global Warming, in particular the rise of CO2, has a strong scientific reasoning behind it that is impossible to deny.
What instead is a whole lot more debatable are the following two points:
- Global Warming is a reality (regardless of it being human caused or a natural effect)
- That human activities are the main cause of global warming.