How serious is the world's situation? Bad enough, says a leading Australian scientist, that the world will have to produce more food in the next 50 years than we have in the thousands of years since civilization began, and will have a tough time keeping up.
But this one comes from Megan Clark, the head of Australia's national science agency, the Commonwealth Scientific and Industrial Research Organisation, or CSIRO. Clark is hardly a wild-eyed extremist; she is a former mining executive.
In a speech in Canberra last week, Clark said growing population will cause exponentially-rising demand, and a warming climate will make the challenge more difficult.
"It is hard for me to comprehend that in the next 50 years we will need to produce as much food as has been consumed over our entire human history," she said.
"That means in the working life of my children, more grain than ever produced since the Egyptians, more fish than eaten to date, more milk than from all the cows that have ever been milked on every frosty morning humankind has ever known."
The so-called green revolution of the last half-century had dramatic results on increasing food production: India alone doubled its wheat harvest from 1965 to 1972, and, as Clark noted, the world overall doubled its food output from 1960 to 2000.
Some parched countries, such as Saudi Arabia, have surprised the world and grown food even in the desert. Lester Brown, president of the Earth Policy Institute and a prominent advocate on world food issues, tells how in the 1970s -- fearful that other countries would retaliate for the 1973 oil embargo with grain embargoes -- the Saudis used their oil-drilling technology to tap deep aquifers. They have used the water to irrigate large swaths of desert.
But Brown says the green revolution has run out of steam. The Saudis admit they are draining those aquifers. The number of chronically-hungry people in the world bottomed out in the 1990s, Brown told ABCNews.com, and is once again rising. Of the 6.8 billion people on earth, he said, more than 1 billion go hungry.
"Most of the things scientists can think of to raise grain yields, they're already done," Brown said. "When you get to the limits of photosynthetic efficiency, there's not much more you can do."
In her Canberra speech, Clark said the difficulty will grow as more and more people move to cities and as a warming climate makes it more difficult to grow more crops.
"Our agriculture is also 16 percent of our national greenhouse gas," she said. When plants and trees are cut down, they release carbon dioxide they had absorbed from, among other sources, cars and industrial plants. And if some environmental advocates have their way, there will be a cost to releasing carbon -- one that even the wealthiest countries will be reluctant to pay.
Melting glaciers and rising sea levels could inundate low-lying rice paddies in southern Asia, and leave others -- from Australia to America -- parched.
"We can no longer simply clear more forest and farm even more marginal land," said Clark.
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."