2) There is already more than enough CO2 for a 'full' greenhouse effect so more will not make it 'worse.'
Please, enlighten me... If that's the case, why does Venus (with a massive atmosphere made mostly of CO2) have a far higher (~400 Celsius) surface temperature, even though it actually gets less heat from the Sun? This might sound surprising - Venus is closer to the Sun, so it'd be natural to expect it to get more heat. However, it is shrouded in a thick layer of clouds that reflect most of the light it receives back into space.
Venus's temperature is only explainable by its greenhouse effect. This can even be measured. So, my question is... if we are experiencing a "full" greenhouse effect, then what IS Venus experiencing?