Recently watched a documentry(BBC Horizon - How Many People Can Live on Planet Earth 2009) and its scary, could be worse than Global warming.. There are almost 7 billion people in the world today and numbers are increasing rapidly. Soon there'll be 8-9 billion people and we'll all feel the impact. (cos each human need water, food, energy, shelter, n hopefully whole lot more) Earth can sustain upto ~15-18 billion people IF everyone consume(water, food, energy) as little as average Indian or Rwandan.. but Earth can only sustain maximum 1.5-2.5 billion people living in the lifestyle of those in US or UK. n these figures are bases on rates of consumption that many think are already unsustainable. "Already today more than 1.2 billion people living with water scarcity." "Even setting aside the moral responsiblity we have to protect other species, if we continue to damage our ecosystems, we damage ourselves." "It's clear that we'll have to change the way we live and use our resources."