On Monday the population reached 7bn. It sounds like a large number, but needs to be put into context. There is a danger, however, in using statistics wrongly. The easiest thing to do would be to take the earth's land mass and divide it per person. That will not be a very good indicator. Little of the land mass is habitable, in the sense it can provide for the resident population. Another way would be to look at population density measures. It works slightly better, but different countries have different proportions of habitable land mass.
For example, UK has 256 inhabitants per km2, while Somalia has 20 (the average for Africa is 34). This does not mean Somalia is under populated, but is probably due to a large part of Somalia is unsuitable for human population. Large populations or population concentration is difficult to describe statistically, but fairly easy to understand when travelling. You have to see it to comprehend it.
The change in population is more worrying. Since 1968 it has doubled. The addition to population is equivalent to entire population of India and China today. In the next 40, or so years, will population grow to 14bn? Well, according to UN estimates, it will approximately be in 2068.
Policy makers have in general avoided addressing population problems. It may be because we move into an ethical dimension, not otherwise present in the policy debate. In one sense, population policy is about determining life. On the other hand, avoiding addressing the problem, has also ethical consequences, some very serious (like the ethnic conflicts in Rwanda).
The unwillingness of policy makers to address the problem is fuelled by mainly two misconceptions. One is that industry needs unskilled labour to do the jobs the domestic population does not want to do. It is all about price. If the firms paid a high enough wage, then the domestic workforce would do these jobs. They simply would not do them at wage paid in the less prosperous part of the world. Increasing the size of the unskilled labour force will not plug a hole in the labour market, but will instead drive down the real wage (what is actually seen today in the UK).
The other misconception is that an increase in the working population can bring about a sustainable pay-as-you go pension system. The idea is that one can tax the young and give to the old. What is forgotten here is that the young is also a political force, and may induce even lower pension payments. Also, the large working population will be a large retired population eventually. Who is going to pay the pensions then?
Population growth is (obviously) not sustainable, and would have to settle at zero at one point (just because the earth is limited). The question is when? Some countries have taken radical steps to control population. China, which has 138 inhabitants per km2, introduced a one-child policy. Rather than command and control, one can rely on the market price system. A family avoids growing too large if there are financial consequences of doing so. The constraint on space must is reflected in the price of space. When a population grows, the price of housing will increase. One cannot build a country out of overpopulation (because land is fixed in size). All it does is to keep the prices of housing down, incentivating a further increase the population. For the price mechanism to work, we need stricter planning laws.
Population growth will stop in one way or another. We have the choice of how.