Bill notes that the reflective capacity of such material depends on where it will be positioned in the oceans. The closer to the equator, the more effective it will be. Snow is now predominantly located close to the poles and appears from the sun as two small rims on the edges of Earth that receive less sunshine than any other area on Earth. Yet, this relatively small snow-covered area acounts for a cooling of Earth of about three degrees Celcius, Bill estimates, because snow reflects nearly 90% of the solar radiation that falls on it. Positioning the material closer to the equator will therefore require less surface than the areas of the poles currently covered by snow -- the closer to the equator, the less surface will be needed, in order to achieve the same amount of cooling.
For more, see: Chemcept on Global Warming