Reflect the Sun's Rays
This scheme goes a step further than the sulfur injection plan, though the general idea is similar. Rather than simply blocking some of the sun's rays, scientists want to reflect them back at the sun by sending a variety of materials up into the atmosphere.
One proposal suggests launching balloons to a high altitude and then spraying them with "reflective" particles. Other groups have proposed that a more dramatic approach is necessary, and recommend deploying a fleet of 3-foot-wide (.9-meter) reflective shields. The cloud of shields would be more than 62,000 miles (99,779 kilometers) long. Eventually, 16 trillion of these shields would be positioned over eight years — at a cost of trillions of dollars.
The negative side effects could be devastating: Reducing sunlight has the potential to make the planet drier. Models have predicted a 1 percent reduction in rainfall for every degree Celsius of warming that we reverse, which has the potential to increase droughts and reduce food production in vulnerable areas. And what becomes of the trillions of shields? That's a lot of debris that could become dangerous as it pollutes space or falls back to Earth, where it would eventually need to be disposed of.