>But, how do you measure and make the distinction between man made and natural phenomena?
I bet you think you're being rational and not just quoting another completely idiotic piece of denialist propaganda.
It's actually ridiculously easy to measure the impact of man-made activity - we've been doing it for decades. You see all carbon are not created equal. The carbon from fossil fuels have a particular mixture of isotopes you don't find in any other source (and nothing except humans burn fossil fuels). The increased CO2 in the atmosphere - consists entirely of carbon that could ONLY have come from fossil fuels - volcanic CO2 for example has a a completely different isotopic distribution.
We CAN tell where it came from. We can tell how much came from where.
Volcanoes are the only other significant source of CO2. The USGS (world's greatest volcano experts) published a paper with the numbers. Total volcanic CO2 per annum 0.025% of what coal plants ALONE add.