With the Earth’s population nearing 7 billion, some of the world’s leading thinkers on nature and resources will gather to explore humanity’s mounting impact on the planet when the Aspen Environmental Forum 2011 opens May 30.

Author-turned-activist Bill McKibben, Whole Earth Catalog founder Stewart Brand, and writer and television host Josh Dorfman are among 80 speakers slated to weigh in on what is needed to provide stable climate, clean air, clean water, and food for a growing civilization. The five-day gathering in the Colorado Rocky Mountain resort, now in its fourth year, is presented by the Aspen Institute in partnership with National Geographic.

The forum will take up the theme of a special yearlong National Geographic magazine series: The population milestone of 7 billion people on the planet that will be reached in 2011, and the growth to 9 billion expected by midcentury. Scholars, business leaders, and policymakers will weigh in on the implications for cities, energy, goods, and nature.

Last year, the still-unfolding BP oil spill in the Gulf of Mexico served as a focus for many of the sessions at the Aspen environmental conclave. This year’s forum opens with a look at the natural and man-made disasters that have made headlines in recent weeks—from the devastating storms in the U.S. Midwest to the nuclear crisis at Fukushima Daiichi—and whether it is possible to build more resilience into a crowded and complex world.

McKibben, founder of 350.org, who will speak at the opening session, says he’ll concentrate on the need to prevent more climate change than people can adapt to. “Once you start thinking about the trouble we're facing, you understand that we need to take dramatic and serious steps to limit the scope of that change,” McKibben said in an email, adding that he intends to discuss the wild weather events of the past year as a case in point.

Brand says that he will have a positive message to convey. “This is going to be an amazing century for Greens,” he said in an email. With the most difficult problem civilization has ever faced before them, he said environmentalists have tools unimaginable just a couple of decades ago—including bar coding for species discovery, sophisticated biocontols for alien invasives, and remote and networked sensing.

Dorfman, who hosts Sundance Channel’s television series, “The Lazy Environmentalist,” said in an email that he hopes to convey the idea that in order to inspire Americans to support positive environmental change, a new communication paradigm is needed. “Moralizing, preaching, and guilt-tripping are out,” he said. “Framing green in terms of people's self-interest is the only way to quickly move the needle and develop massive buy in for positive environmental change.”

Other sessions will look closely at the promise and drawbacks of “clean coal” and natural gas as energy solutions, impact investing for environmental benefit, and the future of forests. As always, National Geographic photographers will show their work: Brian Skerry’s sea images, Diane Cook and Len Jenshal’s look at altered landscapes, and Jim Richardson’s work on preserving mankind’s 10,000-year legacy of food.

This year’s Aspen Environment Forum sponsors include Chevrolet, Duke Energy, DuPont, and Shell.