LONDON, UNITED KINGDOM--(Marketwire - 05/06/11) - AC Generations have learnt that sometime late in 2011 (at least according to the people-crunchers at the U.N. Population Reference Bureau), humanity will reach a new demographic milestone with the birth of the 7th billion living person. That's nearly twice as many people as there were in 1970! As a measure of just how fast global population is growing, the 6 billionth living person, Bosnian Adnan Nevic, is only 11.You can expect the event to be marked by the usual worries; can the planet Earth really support 7 billion people, especially with the population expected to top 9 billion by mid-century? With some 1.5 billion people already living on less than $1.25 a day, nearly 1 billion people hungry and the natural world already heavily damaged, are we on the path to destruction? AC Generations has noticed that we've been growing at a blazing pace and now there really are signs of fundamental limits on things, including the capacity of the atmosphere and ecosystems in the oceans to absorb greenhouse gases. There are biological systems that are hurting.There is one saving grace amongst this though, cities are hugely important and they will make or break this century, in many ways. In other words, if you have functioning cities that are resilient--that can provide basic living standards for people who come there looking for work--they can probably take an enormous amount of pressure off ecosystems and foster much quicker advancement for people. AC Generations has viewed a lot of studies around the world showing that, when you move to a city, access to education increases, access to income increases, and your energy footprint goes down.However as people become less poor and become a little more wealthy--moving through middle class lives toward upper income lives--we develop appetites. The amount of meat we eat goes up, and it's usually working your way up the food chain toward the most energy intense, water intense, land intense sources of food--beef, at the top of the chain, or bluefin tuna at the top of the ocean chain. And that's unfortunate, because again, you can probably fit a billion reasonably wealthy people on the planet consuming at the top of the food chain. But as everyone moves toward that middle class zone, you really do get a sense that something has to give and this is something AC Generations are worried about - What will give??