All serious considerations accepted, no matter how un-PC, immoral, amoral, etc. It needs talking about, and we may as well start here...
To start with 5 years sterilization added to the end of
every prison sentence (and of course during it).
However - our country isn't growing that much so...
Stop immigration and asylum. Not PC at all, but if we prevent overcrowded nations from spilling over to us...
Make the world rich. Difficult to acheive, but rich countries have a lower growth rate in general, so we really need to stimulate third world nations.
Or how about global compulsory sterility, and 'birth' licences to the select few (probably the rich in the end, but a 'fair' system would try to be in place).
Most of these solutions have terrible backlash potential though, so the chances are the ultimate solution to the problem will be:
Natural selection.