Nine billion people: Business bonanza or Armageddon?

Think on the bright side. Nine billion people is a lot of people to sell stuff too. But can the world handle it?

At Fortune’s Brainstorm Green conference Wednesday, business and environmental leaders were cheery.

“I definitely vote for opportunity,” said Glenn Prickett, chief external affairs officer for the Nature Conservancy. “I don’t think you can be in the conservation community and not be an optimist.”

“We all must think of it as an opportunity,” said Jerry Steiner, Monsanto’s sustainability chief. “Otherwise, it will be a disaster.”

Steiner said his company had developed corn plants with much longer roots, which can pull more water out of the ground and more fertilizer, ultimately resulting in more food for these nine billion mouths.

IBM’s energy and environment guru Rich Lechner said his firm is building a water desalination plant in the Middle East that runs on solar power to provide pollution free drinking water.

But Lechner noted the environmental difficulties in a world that is urbanizing at a rate that’s equivalent to building 11 New York City’s each year for the next 30 years.

“It’s going to be a big challenge,” he said.

While business leaders my be upbeat, those that study population are quite nervous.

Adding at least two billion more people to the planet, especially two billion more people that are aspiring to the material wealth of Americans, just can’t be done, said Robert Engelman, a population expert at the research group Worldwatch, in an interview before the conference.

Engelman predicts higher food, energy, housing and water prices for everyone, which will ultimately bring down living standards worldwide.

“There will be lots of innovation,” said Engelman. “But when you look at the scale of what we’re doing to the planet and how rapidly things are changing, it’s really hard to see all the pieces coming together.”

To help head off a less off world, the speakers on Fortune’s panel urged greater cooperation among government agencies when permitting projects, financial mechanisms that make investment less risky for farmers in the developing world, and a greater participation from business leaders from places like China, India and Brazil – especially at forums like the Fortune conference.

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