This year, the world will hit 7 billion persons; by 2045 it will reach 9 billion. At that rate, we’ll reach a global population density of a little more than half of that of France. It’s not an explosion; it’s about resource management.

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The world population isn’t exploding. That’s a key idea I learned from National Geographic‘s awesome article on what the world could look like when it hits 7 billion people later this year in 2011. While 7 billion sounds like a lot (and is) as the article puts it, the world will reach “replacement fertility” — when women have just enough babies to replace themselves — in 2030.

That global slowed fertility rate is due to a variety of things. One of them is China’s one-child per person mandate. Another is planned parenting, education, and economic growth efforts under way in India, the country that is set to exceed China’s population by 2030.

At that replacement fertility rate, the world will reach a 9 billion population by 2045, which will deliver a world population density that will be a little more than half of that of France today, notes National Geographic. In theory, that doesn’t sound too bad. The current world population could actually fit inside Texas … if Texas had the same population density as New York City.

So we clearly have the space. The biggest problem associated with the coming population growth is that by 2030, 1 billion people in the developing world will join the world’s middle class, up from 400 million in 2005, notes the article. Those people in the middle class will naturally consume energy, food, water and other resources at a much higher rate than the rest of the developing world, and closer to that of Americans, Canadians, and Europeans.

The key to global sustainability of this population growth will be figuring out resource management and city planning. As all you greentech entrepreneurs and investors know, delivering resource management is really what is at the heart of the industry’s innovations and technology.

The coming massive energy consumption boom from this middle class will, in particular, be the sticking point, and the biggest opportunity, for energy efficiency and clean power-focused entrepreneurs. A substantial jump in the daily energy consumption of so many people could push us over a tipping point in terms of climate change.

Todd Woody predicts that early stage energy efficiency plays will be big in 2011. Greentech investors seem to have taken some big risks — and failed to generate substantial returns in the near term — in terms of clean power over the past few years. But energy efficiency can be low-capital-intensive (software, behavior change, wireless networks) and is widely available now.

Water technology — from desalination to water metering — will also be a big opportunity for sustainably managing this population growth, as will food and agriculture-base technologies, like biotechnology, and new forms of farming.

It will be city planning and these types of innovations that will help determine what a population of 7 billion, and then 9 billion, will look like. The National Geographic article points out that in Collapse, author Jared Diamond argues the Rwandan genocide was partly a result of too many farmers dividing up a too small a space of land — basically, overpopulation. Some researchers think there will be a global food shortage at 9 billion people.

The 9 billion person world doesn’t have to be some apocalyptic urban jungle; it can be managed sustainably with smart resource management and technology. It’s a massive problem, and an opportunity. And we really don’t have a choice.

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Image courtesy of NASA.

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