Atmospheric CO2 concentration vs dissolved concentration do not correlate like this. The actual balance between the two is based on CO2 partial pressures combined with everything else in the air (N, O, H ect). Since CO2 only occupies a small percentage of the actual air pressure, a change of 200 ppm of CO2 would have very little (if any) effect.

https://en.wikipedia.org/wiki/Partial_pressure

Also look at Henry's law which is of direct interest to the above topic.