For the villager, who asks to be identified only as Bernadette, life is a running battle. On tiny plots of corn, millet and sweet potatoes next to Virunga National Park in the Democratic Republic of the Congo, she and her neighbors scrape a bare subsistence for themselves and their children. Her sweet potatoes, she told us last year, are under constant attack from baboons and elephants that stray from the park in search of food. Deep agrarian poverty of this kind is hard on nature, too. Virunga is home to half of the world's fewer than 900 remaining mountain gorillas, as well as endangered elephants and antelope. The park's forests are under pressure from the charcoal trade, and in 2007 the local charcoal mafia assassinated seven of the park's gorillas in retaliation for a crackdown on illegal logging. Poachers have killed 250 of Virunga's 300 elephants in recent years, probably with the acquiescence of residents fed up with crop raiding by the animals.

Rising affluence over the past several centuries has, overall, been hard on the environment. But on the front lines of conservation, where people live intimately with primary forests, biodiversity hotspots and endangered species, it is often grinding poverty that drives the destruction.

Improvements in productivity, as exemplified by Shigeharu Shimamura's farm in Japan, could hold the key for conservation in the 21st century. Shimamura oversees a 25,000-square-foot farm at the site of a former Sony microchip factory. Everything grows safely indoors. With a combination of water, plant food and 17,500 LEDs, he harvests as much as 10,000 heads of lettuce a day—100 times more per square foot than an ordinary farm—using 90 percent less water and producing 80 percent less waste. Humans use about half the world's ice-free surface, mostly for food production. Yet with continuing technological improvements, population and its impact on the environment could peak and then decline within the next few decades.

This phenomenon, called decoupling, means that people can increase their standard of living while doing less damage to the environment. Protecting remaining wilderness in the face of escalating demand for food, resources and energy will require accelerating decoupling—in other words, speeding up urbanization and intensifying modern agriculture. The idea may seem counterintuitive, but especially in the developed world, much of the harm that people inflict on the land has begun to flatten and even decline. Today, for example, humans require just half of the farmland per capita that they did 50 years ago. As a result, across much of the U.S. and Europe, marginal farmlands are reverting to forest.

Social changes will amplify these trends. More than half of humanity now lives in cities, and that figure could reach 70 percent by midcentury. When rural populations move to cities, birth rates tend to fall dramatically. That is why many demographers expect human population to peak and then decline before 2100. The rural exodus drives other, mutually reinforcing efficiencies as well, increasing both economic and resource productivity.

The implications for 21st-century conservation efforts are clear. Parks and protected lands remain part of the solution. But without tackling the demand side of the equation, real habitat protection will be difficult if not impossible. Success will require substituting human technology for natural resources. It will also require modern energy. Nearly three billion people still rely on solid fuels such as wood and dung. Moving all of humanity to energy technologies that are cheap, clean and abundant will improve their well-being without harming the environment.

Tools for shrinking our environmental footprint are in plain sight. Seizing those opportunities will require conservationists to focus on infrastructure and technology policies that traditionally fall outside their purview. Without accelerated decoupling, protected areas can't resist growing human demand for food and energy, and the elephants and gorillas of Virunga may face doom.