If American stocks are outlandishly expensive, for instance, look abroad. A prime example: A few years ago, Grantham estimated that stocks in emerging markets were cheap. So he loaded up and then benefited as equities in developing countries ­outperformed almost every other market sector.

It's those same global instincts that fuel his passion for protecting the environment - in small ways, like with the few hundred acres he and his family own in Panama that he's currently replanting with a variety of trees, and in larger ones, like with his foundation's newly minted prize that it was recently awarded for environmental journalism. "He's a very smart philanthropist," says Carter Roberts, president of the World Wildlife Fund in Washington, D.C., the world's largest privately financed conservation group. "He's always pushing and prodding me to find the right solutions. Not just by creating parks on the ground in places like East Africa or the Amazon, but in getting companies in the U.S. to source their timber and paper in a more sustainable way. It's really remarkable."

Indeed, Grantham now dreams of harnessing the power of the media to change public attitudes about the environment on an even grander scale, much like former vice president Al Gore seems to have done with his film on global warming, An Inconvenient Truth, which brought a key message to a mass audience. If public attitudes can be altered, Grantham hopes enough pressure can be brought to bear change in government behavior. And then there might be some real hope that we won't burn through all the earth's resources before we realize it.