What if we could solve the problem of global warming by just scrubbing the air clean of carbon dioxide, before it has the opportunity to add to the blanket of greenhouse gases smothering the earth? Canadian professor David Keith, the 2006 Canadian Geographic "Environmental Scientist of the Year," believes we can do exactly that. He's building a prototype of a machine that will eventually be almost 400 feet high. It will suck ambient air into one end and spray it with sodium hydroxide solution, then expel clean air out the other end. Keith thinks he'll prove that his machine will be even more efficient than trees in cleaning C02 from the air.