We can cool the Earth, but the technique I propose will cause more problems in the 2,000 year long run than it solves in the 50 years it would take to fully implement the plan. We can cool the atmosphere over the oceans and thus the air flowing over the continents by bringing large quantities of the deep ocean water to the surface. In addition to that cooling we can take some of that ocean water and spray it directly into the atmosphere at a modest altitude.
Those two cooling actions can be done by pulling the deep water to the surface with a plow-like device and by pumping water to an altitude. The energy powering these actions can be gathered using large kites. These wouldn’t be children’s kites but very large ones specially designed for stability and a sustained dragging action. They would drag an underwater plow which would scoop water from an ocean depth, where the water is quite cold, and pull it to the surface where it would be spread and mixed with the warm surface water. These actions are surprisingly low tech, but to maintain stability in a turbulent world it would use sophisticated sensors and control ailerons.
These kites located at some modest altitude, which would vary depending upon the conditions, would also be used as dispersion platforms for spraying into the air water that was pumped up to them. This water would evaporate before falling back into the sea and would form clouds and the clouds would reflect sunlight back into outer space and that would create an additional source of global cooling. The energy for operating the water pump would be generated by a propeller being pulled through the water by the kite as it drags the plow.
Once launched these systems could be remotely operated and because they are easily tracked using GPS and controllable they could be set on routes that would traverse the oceans in very remote locations for years untended. Thus they would be cheap to operate for years on end.
There are problems with this solution to global warming as there are with all solutions; but the biggest flaw with this solution is that it doesn’t approach the underlying problem, that is our huge human population and its ongoing explosion. This proposed method of cooling the Earth might permit humans to continue over-exploiting the planet until something else breaks; but something must fail because infinite growth is impossible. If everyone wants to live like current Americans then the ultimate population must drop. Gasp! To have a permanent solution to humanity’s problems we must stabilize the human consumption of resources to something that the Earth can sustainably provide.