Overpopulation: You get to cast the deciding vote.

[Exian]

You've constrained the options to such a point that its no longer a "Sofie's Choice". It's easy, put a legal limit on reproduction, and have sterilization become a part of the birthing process. All other options have been explored, as you have stated, and the only other option, if not this, is mass starvation.

The fallout would be almost immediate with libertarians and the like revolting, which would lead to some sort of war, but it's unavoidable, as a legislator. The other method is effectively doing nothing.

Now, if I took myself out of this hypothetical and answered as myself, I'd do nothing. Worse things can happen to this planet than humans dying out. And since I'm breaking rules, I might as well bring the economy into the equation. If food is rare, food is expensive. If food expensive, people are expensive. A large portion of people, who are either calculative about their movements, thus careful with their reproductive decisions, or just selfish, thus dictating their choice to have more children, will counter balance the amount of people on earth. We are already seeing this trend.