points. For example, you erroneously suggest that water vapor is ignored in climate science. That is patently false. It is vitally important to understand the relative strengths of greenhouse gases and the difference between a forcing and a feedback. A forcing is something that disrupts the radiative energy balance between the earth and the sun, a feedback is something that responds to a change in temperature to amplify or hinder that change. Water vapor traps heat much more effectively than CO2, but is a feedback, not a forcing. If we somehow were able to drain all of the water vapor from the atmosphere it would be rapidly replaced through evaporation. Likewise, if we injected massive amounts into the atmosphere, it would rapidly precipitate out. The amount of water vapor that the atmosphere can hold is governed by pretty basic chemistry. The warmer the atmosphere, the more water vapor it can hold. Thus warming by CO2 triggers a positive feedback by allowing more water vapor into the air which traps more heat. This makes CO2 the control knob.

Next you compare human to natural CO2 emissions completely ignoring the CO2 that nature absorbs. 

It is true that nature produces much more CO2 annually than mankind. The inconvenient truth that is always left out by those peddling doubt is that nature also absorbs enormous amounts of CO2. If a river delivers 100 gallons of water a second to a reservoir, which has a dam capable of releasing 100 gallons per second, who is responsible for the lake overflowing if I turn on my fire hose and deliver 4 gallons per second? The absorption/emission of CO2 from all sources is known as the carbon cycle.What causes build up in the atmosphere is disruption of this cycle. Figure 6.1 from working group 1, chapter 6 of the IPCC AR5 report summarizes it nicely: 

Compute the total flux into the atmosphere and you will find an imbalance of 3.8 of their units entering the atmosphere, compared to the 7.8 that mankind emits through burning fossil fuels. That means that nature is able to cope with roughly half of our carbon emissions and is a net CO2 sink. In other words, we only have to reduce global emissions by roughly 50% to stop the increase in atmospheric CO2. Of course this is not without cost, excess carbon absorbed by the ocean leads to ocean acidification. It is mankind that is responsible for upsetting the balance in the carbon cycle, despite nature's best efforts to compensate for our emissions.