The Sky is Warming! The Sky is Falling!

Many people have come to believe that global warming is the most serious threat facing human beings in the next few hundred years. On the other hand, the planet also faces global peril on the same scale from natural causes - such as a large asteroid impact. Yet which one is a more scientifically demonstrated risk? Dr. Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics has an interesting answer.