“Solar Radiation Management describes a suite of proposed technologies that aim to reflect sunlight back into space before it warms the earth’s climate. These proposed technique would achieve this in one of a number of ways: by spraying sulphur dioxide or hydrogen sulphide into the stratosphere (the upper reaches of the atmosphere), by launching a 300 km2 barrier into heliosynchronous orbit, by making the albedo (reflectivity) of clouds, or by launching billions of reflective balloons into the stratosphere.”

http://www.geoengineeringmonitor.org/cat/technologies/solar_radiation/