Half a century ago, a campaign to boost agricultural production using new, high-yield seed varieties swept Asia and Latin America, rapidly doubling the amount of wheat, rice and other staple crops those regions produced and helping lead to years of nearly worldwide food surplus and plenty. Today, with developing nations facing renewed hunger and even riots amid a potential global food crisis, experts agree that a new Green Revolution is needed to offset the challenges of population growth, biofuel demand, extreme weather and a growing clamor for costly-to-produce meat and milk.