From what I can see the only long term solution to overpopulation is migration. Consider that in 2004 the UN projected world population to be 9.2 billion by 2075.
A few years back the wheelchaired one mentioned he believed if we could hold off the inevitable crash due to resource scarcity for about 150-200 years we'd be good to go.
The conservative luddite thinks we need to step up space exploration
Pete