There are others who say such worries are overblown, and that because of genetic engineering and other advances, there will not be vast increases in the numbers of the world's hungry.
Bjorn Lomborg, author of "The Skeptical Environmentalist" and "Cool It," has argued that there are really much more pressing priorities, such as disease.
"Yes, global warming might slightly slow food production, but the claims are vastly overplayed, and again -- if our concern truly lies with food security and the world's hungry -- lead us to focus on the wrong solutions," he wrote.
Clark herself said she was confident that biotech companies would come forth with new innovations, and greater concern about protecting against hunger.
So which point of view is right? Perhaps both -- and neither. Clark argued that human ingenuity has gotten us out of tight fixes before. But Brown said this time may be different, with a crowded world and a warming climate.
"Maybe someone has a solution," said Brown, "but they'd better hurry."