<P> Many science fiction authors, including Carl Sagan, Arthur C. Clarke, and Isaac Asimov, have argued that shipping any excess population into space is not a viable solution to human overpopulation . According to Clarke, "the population battle must be fought or won here on Earth". The problem for these authors is not the lack of resources in space (as shown in books such as Mining the Sky), but the physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth . However, Gerard K. O'Neill's calculations show that Earth could offload all new population growth with a launch services industry about the same size as the current airline industry . </P> <P> The StarTram concept, by James R. Powell (the co-inventor of maglev transport) and others, envisions a capability to send up to 4 million people a decade to space per facility . A hypothetical extraterrestrial colony could potentially grow by reproduction only (i.e., without any immigration), with all of the inhabitants being the direct descendants of the original colonists . </P> <P> Despite the increase in population density within cities (and the emergence of megacities), UN Habitat states in its reports that urbanization may be the best compromise in the face of global population growth . Cities concentrate human activity within limited areas, limiting the breadth of environmental damage . But this mitigating influence can only be achieved if urban planning is significantly improved and city services are properly maintained . </P> <Ul> <Li> <P> Afghanistan shows a classic youth bulge . </P> </Li> <Li> <P> Angola shows the same, even more pronounced . </P> </Li> <Li> <P> China had an extreme youth bulge until the 1960s, when it sharply curbed partly as an effect of the one - child policy . </P> </Li> <Li> <P> Compare the population pyramid of the USA which was bulging until the 1960s and has steadily slimmed since . </P> </Li> <Li> <P> A population pyramid based on the 2011 Libyan population . </P> </Li> </Ul>

What is the current population on earth and why is this a concern