We have the technology, knowledge and surface area to support a population quite a lot larger than what we have right now. I would argue that we have an en-masse lack of forsight in terms of how we're proceeding with the issue.
(Most) Governments in the developed world seem to be more concerned with the avoiding economic hit of taking action to address any of the large future issues (overpopulation, climate change, etc), without considering the economic hit of NOT taking action. The electricity needs of humanity can easily be generated with current solar technology (improvements need to be made to national/continental grids but that doesn't change the fact). The food requirements of humanity can easily be produced with usable farm land by focussing on growing crops rather than rearing livestock (similarly, distribution is a problem but not an insurmountable one).
Both of these issues with regards to overpopulation can be addressed with massive expenditure from the developed world and obviously the immediate economic effect would be bad. What will be worse though will be the effect of doing nothing and carrying on as we do now. Perhaps if we had more scientists in government rather than economists then we could actually get something done...
You've oversimplified br0..
The problem is people, and the people's problem is coordination..
People are epic inefficient.. and generally hampered by lethargy, complacency, and lack of follow through.
Everyone knows the right thing to do, but only spartans had the resolve to do them, and yet they're all dead..
So.. why is this.. well, because of the constant infighting...
The real battle is with not only nature, but our inner termoils.. our propensity for vices and to sin..
There is also a grave misunderstanding of MONEY... That number @ da-Bank is just a fictional score-board, WE DO NOT have that equivalent in Industrial or Human capital...
That is why, we can't just write Africa a Check for 10 billion dollars, and have the problem go away....