This NY Times article looks at different techniques of geoengineering: rearranging the earth's environment on a large scale to suit human needs and promote habitability. I think there needs to be more research in this direction to give us more options if global warming becomes a serious problem. Some ideas that they are looking at to cool the world:
His paper newly examines the risks and benefits of trying to cool the planet by injecting sulfur into the stratosphere.via NY Times
Dr. Angel outlined a plan to put into orbit small lenses that would bend sunlight away from earth — trillions of lenses, he now calculates, each about two feet wide, extraordinarily thin and weighing little more than a butterfly.
Other plans called for reflective films to be laid over deserts or white plastic islands to be floated on the world's oceans, both as ways to reflect more sunlight into space.
Another idea was to fertilize the sea with iron, creating vast blooms of plants that would gulp down tons of carbon dioxide and, as the plants died, drag the carbon into the abyss.