More oxygen?
Oxygen is even more essential to OUR survival but I guarantee you wouldn't like the effects if we increased it by 40% in our atmosphere like we have CO2.
It is well recognized that increases in CO2 are a feedback of warming. That is true but it in no way says that increasing CO2 levels through other means can't cause warming. It's not a binary either/or situation.
Using your numbers atmospheric CO2 is increasing by a bit less than 5 ppmv/year however if you look at total human caused emissions of CO2 it would be enough to raise levels by around 10 ppmv/year so a bit more than half of CO2 emissions are being absorbed by other sinks in the carbon cycle. We are increasing the total carbon in the active carbon cycle which raises the level everywhere.
In your "simple maths" calculation you totally ignore the sink side of the carbon cycle. For about the last 10,000 years CO2 levels in the atmosphere hovered around 280 ppmv varying up and down by around 10 ppmv on a yearly cycle and only when humans started significant combustion of fossil fuels (and to a lesser extent certain land use changes such as deforestation) did the level in the atmosphere start increasing.
