I'd like to hear more of what Rolando (Wyvern) has to say on the matter, since he is a scientist.
My position is on the hard edge-don't give a damn.
As much as Earth's climate had experienced severe changes in the past way before mankind existed or had a way to impact the ecosystems I DO believe that pollution coming from emissions, our waste, deforestation and other situations caused by human activity to expand their living environment is deteriorating our planet at an accelerated rate.
Of course we can make an experiment for a complete year nobody will use cars, planes, trains or any locomotive vehicle pushed by oil fuel. No electricity will be generated by thermic plants (depending on diesel), no ozone depleting gases will be emitted during that year, not a single tree will be cut or any forest fire will be allowed to spread. Cement factories will not produce clinker in a whole year, there will be no space exploration or explosions of any type be allowed (thus a year of full peace).
No plastic containers will be dumped and no toxic waste will be generated in anyway (including paint, drugs/medical, tires and many more industries). Let's live a whole year like in the 15th century (but picking up the crap from the horses and dispose it as manure) and sorry but chimneys are not allowed during winter sorry for those on cold climates.
We can measure the gases and other pollutoon indexes before and after the year and see what effect do we have on our planet. Ah and we can expect Santa Claus to give everybody in the planet a gift for being good for a whole year.
Sorry if I sound that depressingly fatalist and sarchastic, can't teach an old dog new tricks. I'm not going to give up my car, my flight to PPIX, my Coke on plastic bottles, the toilet paper or the paper I print on. I like my wood furniture, and frankly I don't give a damn where my waste is going as long as is not my backyard. Since I have no offspring I feel no obligation in leaving it to anyone. Besides Mama Nature will always find a way to change the things long before we driven ourselves to extinction.