BANGWEULU WETLANDS, Zambia – Out here on the endless swamps, a harsh truth has been passed down from generation to generation: There is no fear but the fear of hunger.

How to stop climate change while expanding energy production is one of the biggest challenges in global development. Doing so requires all kinds of improvements in efficiency – from reducing the amount of electricity lost in transmission to better motors and lightbulbs. But, as demonstrated by recent efforts in the Pentagon, changes to how people work may be the lowest hanging fruit.

Population projections undergird many important policy decisions, from the U.S. government’s Feed the Future program to the Sustainable Development Goals. But they’re not as straightforward as they appear. Demographers often base their estimates on complicated assumptions that aren’t obvious to the end user.

“There is no magic bullet or solution to resolving climate change quickly,” said the Population Reference Bureau’s Jason Bremner at the Wilson Center on October 28. “Our next 100 years will be far different from the last 100 or the last 1000…and it has become clear that nations will have to pursue many strategies in order to reduce emissions, build resilience, and adapt.” [Video Below]

“We don’t know the reason for the death of fish in downstream villages,” Hamberton Nongtdu, a mine owner from the northeastern Indian state of Meghalaya, told me.

On the heels of a landmark U.S.-China climate agreement, 2015 will be a critical year for China’s environmental and energy policy. A revised and much stricter Environmental Protection Law went into force on January 1; new amendments to the Air Pollution Law are likely to be put in place; and the National Development and Reform Commission will draft a new five-year plan.