What kind of harm is done to plants if CO₂ concentration goes beyond 0.05%?

Increase in CO₂ concentration beyond 0.05% will lead to the dominance of C3 plants such as trees. This is because under elevated CO₂ concentration, C3 plants do photosynthesis in much faster rate than C4 plants, thus growth of C3 plants will be more. Biochemical and physiological reason behind this phenomenon is that under present atmospheric CO₂ concentration (around 0.03%) , the enzyme rubisco, which fixes CO₂ in plants is fully saturated in C4 plants and is much below the saturation point in C3 plants. Therefore, rate of photosynthesis increases in C3 plants with increase in concentration of CO₂.