"What we're going to have to do at a global scale is create a new system," Gates said in a speech at the TED Conference in Long Beach, California. "So we need energy miracles."

Gates called climate change the world's most vexing problem, and added that finding a cheap and clean energy source is more important than creating new vaccines and improving farming techniques, causes into which he has invested billion of dollars.

The Bill & Melinda Gates Foundation last month pledged $10 billion to help deploy and develop vaccines for children in the developing world.

The world must eliminate all of its carbon emissions and cut energy costs in half in order to prevent a climate catastrophe, which will hit the world's poor hardest, he said.

"We have to drive full speed and get a miracle in a pretty tight timeline," he said.

Gates said the deadline for the world to cut all of its carbon emissions is 2050. He suggested that researchers spend the next 20 years inventing and perfecting clean-energy technologies, and then the next 20 years implementing them.

Source ----> http://www.cnn.com/2010/TECH/02/12/bill.gates.clean.energy/index.html