But if the blanket is only a few nanometers thicker does it matter? The amount of CO2 in the atmosphere compared to water vapor, a much more effective greenhouse gas, is insignificant and its increase over two or three decades is tiny.
The earth may be warming right now. It may cool in the future. Humans are simply uninvolved as a causative agent in either process.
It may not. The mean path for an IR photon emitted from the earth's surface is something like 50 meters before it hits a CO2 molecule. At that point the CO2 warms neighboring molecules (mostly O2 and N2). As you say water vapor performs that in far greater quamtity. But in cold dry air the CO2 may be comparable, and the distance of that path means that the CO2 blanket is real, as thin as it might be.
The real argument over CO2 boils down to this: is water vapor the controlling factor for earth's equilibrium temperature and everything else follows? Or does the slight CO2 warming cause a bigger increase (by 2 or 3X) in water vapor.
Everything I know about weather leads me to the former. It is the distribution of water vapor (whether it is even or uneven) that determines the equilibrium temperature. Ultimately the control is solar activity controlling the jet stream and other weather phenomenon.