The rise from 0.028% to 0.042% currently is almost entirely manmade. Without deforestation and fossil burning the rise would have been from 0.028% to about 0.03% or a bit higher, from ocean warming following the Little Ice Age. The idea that 95% of CO2 is natural comes from the annual cycle. There is at last 20 times more natural CO2 created each year than man-made. In the autumn. But the same amount is absorbed in the spring, by nature. So it doesn't add to the total over the years.
If there is more CO2 in the atmosphere, would that promote plant growth? If the planet warms up because of more CO2 in the atmosphere, would that promote plant growth?
If there is more plant growth, would plants use more CO2?
Would the atmosphere reach an equilibrium between the extra CO2 humans create and the extra CO2 the plants use?