The deniers will point out that the vast amount of CO2 emissions are naturally occurring (95-97%?).
Yes, but they'll never point to some actual process that would explain the increase from a "natural" point of view. Increase in volcanic activity? Nope. Hasn't increased. Massive decrease in plant life? That's not natural, sorry. Increases in global forest fires? With less forest to burn than ever before, and humankind working like crazy to put them out when they happen, that seems like a stretch. Some natural chemical reaction? OK, be specific please. Aliens? Magic? Bigfoot?
On the other hand, we can measure
the amount of crap that's coming out of cars, ships, coal-fired electrical plants, factories, etc etc etc etc etc and we can calculate how much we must be producing globally (certainly within an order of magnitude) and it's more than enough to account for 100% of the CO2 increase.
So the denialists continue to scream "no it ain't neither", but never come up with any specific alternative.
And yes, I realize that I'm turning this into a political debate
I may have to move it yet.