At the heart of the Enlightenment was the notion that through science and reason the human condition could be improved in perpetuity. Infamous British killjoy, the economist Thomas Malthus, put a damper on that idea with his 1798 prediction that population growth would someday outstrip the earth's resources and that humans were thus doomed to fight for the last crumbs of the earth, keeping further population growth at bay by the simple math of limited food for an expanding population.

Through science and reason, we spent the last 200 years innovating our way out of that fate. Changes in family planning, women's rights, and economic incentives continue to slow the rate of global population growth. But seven billion inhabitants today are staring down a population of nine billion by mid-century. The number of inhabitants grows in our world of finite resources.

New technologies and new ideas haven't just made life on a planet of seven billion easier. They've made it possible, and will continue to do so. But the Malthusian prediction ever-looms on the horizon. What steps are being taken today to keep Malthus' population theories from becoming truths?

Today's change-makers and problem-solvers square off with variations of the same problems that have faced thinkers before them. Innovative solutions have proven predictions of doom wrong time and again. Yet keeping Malthus at bay for two more centuries, amid daunting, interconnected global challenges, will require even more creativity than before.

With the gains of the Green Revolution have come new challenges. Rising food prices are exacerbating food insecurity in areas already plagued by hunger, and "causing hunger to spread to places that we previously would have thought unlikely," like cities and developed countries, says to Dr. Helen Gayle, President of CARE-USA, a leading anti-poverty organization.

About 40 percent of the world's food production comes from irrigated agriculture, which accounts for 70 percent of freshwater withdrawal worldwide. "Water is connected to our whole global economy--everything we eat, we touch, we wear, has water embedded in it," says Sylvia Lee of the Skoll Global Threats Fund. A growing global population will only increase demand and already nearly a billion people lack access to clean water.

The global industrial food chain consumes 30 percent of the world's energy, and alone produces 20 percent of its greenhouse gas emissions. For the moment, industrial agriculture is dependent on cheap fossil fuels as a source of both energy and fertilizer, putting food security in peril as those fuels become scarcer and climate change threatens to destabilize food systems around the globe.

The situation may appear dire but as the devoted Malthusian Charles Darwin articulated, there's nothing like stress on a population to inspire innovation and adaptation. Addressing sustainability issues "drives innovation," said Shell Oil president Marvin Odum. "Mitigating those risks often drives you right back into the technology loop -- back into asking how can you solve novel problems in novel ways, and how can you do it at affordable cost?"

Join us over the next few weeks as we tackle these challenges as part of this series dedicated to our global population explosion--and the potential solutions that will accelerate us into the future.