This is called Geoengineering and most proposals mimic some form of natural effect that reduces net energy absorbed by the earth. It actually is significantly cheaper to reduce the physical effects of greenhouse gas emissions than it is to reduce the greenhouse gas emissions themselves. Cloud ships which turn seawater into clouds to reflect light back into space before it hits the darker ocean beneath sounds like an interesting plan, but the issue with geoengineering is it does little for ocean acidification.