When you are Bill Gates -- directing a foundation with assets larger than the GDP of 104 countries -- your enthusiasms get amplified on a global scale. Six or seven years ago, Gates read a book by Gordon Conway, "The Doubly Green Revolution: Food for All in the Twenty-First Century," which argued for a second green revolution, this time in Africa. The Bill and Melinda Gates Foundation has since devoted several hundred million dollars to this cause. It is now on the policy agenda of the president, the secretary of state and the G-20, which recently pledged $22 billion to help poor farmers increase their productivity.

During a recent conversation, Gates described himself as a "city boy," but spoke with typical, wonkish intensity about wheat rust, marker-assisted selection and finger millet outputs. "The world moved away from a focus on seeds and plant disease in a dangerous way for 20 years," he told me. Gates is determined to push a revival.

His reasons are strategic. Approximately three-quarters of Africans are employed in agriculture, but about 30 percent of people on the continent suffer from hunger and malnutrition. Over the next few decades, African farmers will need to feed a growing population without expanding into ecologically important lands, while adapting to climate disruptions that make drought, pests and floods more common. They will need Gates' help, and more.

There is a precedent. The first green revolution -- driven by the use of better seeds, fertilizers and pesticides -- was arguably the greatest humanitarian achievement in history, saving the lives of an estimated 1 billion people worldwide. Starting in the 1960s, farmers doubled, tripled, even quadrupled their productivity. But the revolution missed Africa.

In Africa, says Gates, "it won't happen as quickly as late-'60s India, or early-'80s China. ... Africa is not just missing seeds, which is the coolest thing." It also requires less-cool things such as "roads and markets ... extension services and education about best practices."

But seeds are part of the need. The better breeds of the first green revolution are not as relevant to Africa. "In India and China," says Gates, "corn, wheat and rice are over 80 percent of output. In Africa, these are 40 to 50 percent. There are a ton of other things -- cassava, sorghum, millet." Improving the crops of the poor has not gotten much focus from scientists and agribusiness. In addition, Africa "has more variety of ecosystems -- you see huge variations," which demands more hearty seed varieties of every type. So Gates is attempting to fill a gap -- to encourage both the development of crops ignored by the market economy and the provision of those crops to Africans, royalty-free.

Most of this innovation is done through traditional breeding methods. But about 5 percent of Gates' agricultural funding goes to the genetic modification of crops -- a practice he vigorously defends. "The benefits of genetically modified crops have come slower in general than people thought, even in the U.S.," he told me. "But they are starting to show good results." Gates cites the genetically aided development of a strain of rice that can survive for two weeks under floodwaters.

Will the resistance to genetically modified food by European regulators, activists and media be a problem? "It could be a big obstacle," admits Gates. This opposition began "at a time when the benefits (of this technology) were small -- tomatoes that lasted longer on the shelf -- and at the same time as Chernobyl and mad cow disease. People wondered if scientists were tough enough on themselves about the risks they were creating. Now the benefits are likely to come -- offsetting the damage of climate change, addressing the situation of the poor. The maturity of science is greater and the experience with these crops has been very good."

Gates' push for a second green revolution demonstrates much about his philanthropic method, which is non-ideological and results-driven. His faith in scientific progress is admirably old fashioned. It is trendy in some quarters of the environmental community to accept the grave warnings of science on global climate and ecological breakdown, but to dismiss the promise of science in addressing great needs. Protesters attack "Frankenfoods" and trash fields of genetically modified crops -- imposing a cost they will not bear themselves.

"A lot of stuff we do," says Gates, "is based on optimism about innovation for the needs of the poorest." And the poorest benefit because Bill Gates finds seed varieties cool.