It's going to cost trillions of dollars to rework the energy sources all over the world. Were going to have to move away from fossil fuels.

Even if we didn't have greenhouse gases, were going to have to move away from fossil fuels, as we're going to run out. They're finite, whereas solar and wind are infinite.

Some solutions are relatively simple and would provide economic benefits: implementing measures to conserve energy, putting a price on carbon through taxes and cap-and-trade and shifting from fossil fuels to clean and renewable energy sources.

The sooner we get started with alternative energy sources and recognize that fossil fuels makes us less secure as a nation, and more dangerous as a planet, the better off we'll be.

I think that the world is in the middle of a huge transition that we have to make to renewable energy. We have to transition away from fossil fuels very, very quickly.

It's as certain that as long as fossil fuels are the cheapest energy, we will just keep burning them.