A stable number of humans on the planet doesn't necessarily mean less impact on the environment. But it helps.
The world's population is expected to reach equilibrium by mid-century.
The stable growth rate will not mean a cure-all for the planet's health.
Generally, the more affluent a society, the more it consumes.
By the middle of this century, the human population may reach an equilibrium, called the replacement level, where births equal deaths, according to UN projections.
But considering that two countries already at or below replacement levels, the United States and China, are also major polluters, will a stable population number really be better for the Earth?
"Population stabilization is not a cure all, but without it, it will be hard to solve much of anything else," John Seager of Population Connection, an organization dedicated to encouraging reduced global population growth, said in an interview with Discovery News.
Dealing with population increases while improving the living standard of the world's poor, yet avoiding environmental degradation, is like juggling chainsaws, said Seager. It's possible, but very difficult.
The "Impact Population Affluence Technology" equation provides a model of the juggling act, said Seager. It goes like this: Impact = Population x Affluence x Technology.
"Generally, the more affluent a society is the more it consumes... Technology can work both ways. If you buy a brand new giant SUV, your impact goes up. If you buy a hybrid your impact goes down," said Seager.
As the population part of the equation goes down it can allow increases in the other two without increasing the net impact on the planet.
"If the developing world reduces population, it provides more time for heavy resource use," Hania Zlotnik, Director of the United Nations' (UN) Department of Economic and Social Affairs Population Division, told Discovery News in an interview.
"The dilemma about the billion people in Africa, is that they must increase production and consumption [to increase their standard of living]. They must consume more, and that means more strain on environment. They deserve it because they haven't had the chance," said Zlotnik.
In nearly every country, the fertility rate, or average number of children per woman, is already dropping, said Zlotnik, and the UN's projections for continued reductions are fairly reliable since they are based on the central trend of computer models of 100,000 different possibilities.
"It's not like stock market, where anything can happen. The patterns are fairly stable over time," she explained.
But there are no guarantees.
"We are at a very important point, because relaxing on activities to reduce population growth will just bring greater challenges," Zlotnik said.
The practicalities of reducing population growth involve fulfilling the unmet family planning needs of millions of women. Over 35 percent of women in some nations, such as Ghana and Haiti, would like to use family planning but lack the resources, according to UN figures.
Access to voluntary, affordable and understood methods of birth control can bring about transformation in less than a generation, said Seager.
He mentioned the United States, Mexico and Iran as three examples of very different cultures that all reduced fertility rates through purely voluntary methods.
"As families become smaller, education improves. That leads to the human capital necessary to meet environmental challenges," said Seager.