So many points made I would simply say this, what happened in the past is to be aware of however because as civilisation has developed, cutting down trees and belching toxins into the air surely there will be some impact? The internal combustion engine has only been around for a 120 years or so however the growth it experienced from the 50s has been phenomenal, are you suggesting that man made emissions have no impact, if so I remember the impact of smog in the late 50s. Early 60s, thing is you could see it we decided to introduce smokeless zones, not because of global warming but because of the impact on individuals health! There can be little doubt that our desire to continue blindly going into development and expansion brings with it problems. And yes if we all want to heat our homes to 20c + surely that will have some impact on external temperatures too!