according to whose figures? the world bank's methinks. why do you quote this as fact? what is "overpopulated?
overpopulated by rich bankers perhaps

My understanding is that the world is not overpopulated - I guess it depends on what measuring system you use to determine this. There is enough food to feed the world many times over, for example - but with food production systems largely in the hands of agribusiness, it continues to serve the profit motive of a few and not the needs of the many.

Meanwhile there is of course the issue of CO2 production, and naturally this goes up as the population increases - but we have known for a long time that human ingenuity could solve this problem if the political will existed. I'm not into plugging books but Monbiot's "Heat: How to Stop the Planet Burning" - which I've just finished - is an excellent layman's guide to just that. In much the same way as food production, though, the difficulty is getting past the profit-seeking short-termism that directly encourages continued pollution.

Perhaps when some people say "overpopulated", it's a shorthand for "the elite intends to stay with the greedy status quo, so the only other solution is to blame ordinary people".