That is an old argument from the denial side, and I don't even think it is worth consideration anymore, because your bull-in-a-china-shop approach is to compare raw numbers from an unlisted source and use a gap in size to imply that the human component is not worth considering. BUT, if our contributions to GHG increases is enough to tip the balance of nature and throw the earth's carbon cycle out of whack, then whatever the percentage of human sources is....it's enough to push beyond what nature can handle.
*let me add another factor rarely mentioned in climate change debates: an examination of paleoclimate is inexact, but clearly shows a long progression over vast stretches of time, with much higher carbon atmospheric levels in the deep past, near the beginning of life on earth. We do know that the sun burned with about 2/3rds of the intensity back then as it does now, so before 2 billion years ago, there was little oxygen in the atmosphere, and a lot of heat-trapping methane, along with carbon dioxide.
The early deoxygenated atmosphere was adapted for producing high levels of heat-trapping gases to prevent the earth from freezing. As the sun slowly increased intensity, the earth warmed, and the quantity of oxygen-producing plant life increased. During times when too much oxygen was being created, temperatures plunged and ice sheets covered all of the land surfaces of the planet, causing mass extinctions of life.
Once everything balanced out to turn earth into a world where earth would have to prevent carbon buildup, more oxygen in the atmosphere eliminated methane almost entirely and cut the amount of CO2 down to a fraction of what it had been before. During the Pleistocene Epoch that ended 10,000 years ago, CO2 levels fluctuated between 180 and 300 ppm for the past 2.5 million years. The only periods where CO2 levels exceeded 400 ppm since the Cenozoic era began have been accompanied by extinctions. So, in our time right now, we have set the dials for all of the ice on the planet to melt...except possibly for the East Antarctic Ice Sheet, and for marine species to migrate to northern waters because...according to a recently released study, fish are leaving the tropics because oxygen levels are declining to a point where they have trouble absorbing oxygen with their gills. Algae also die off and that will leave deoxygenated tropical oceans that will turn into anoxic swamps, and kill off marine life as it expands towards the poles. Land species have migrated north and south also to escape the heat and become extinct...but all the shit we have built in the past 2 or 3 centuries, plus our large populations and fenced off agribusiness leaves barriers for animals trying to escape the tropics already.
Because whatever the human contribution is for AGW (I'm assuming it's much higher than your dubious oil-funded sources will tell us) the natural environment was able to absorb and sequester the additional carbon being added by humans to keep atmospheric CO2 from rising above 300 ppm.
So, where do we go from here? And can this road to disaster be stopped in time to prevent the mass extinction from taking all of us out with it?