Or they could just stop immigration from third world countries. Families of 10 with the single goal of increasing their carbon footprint by a couple orders of magnitude. But I am sure there are many cities in the US that need more traffic, many suburban areas that need to become more densely populated and sprawly, and tons of rural communites that really need to become urban, one thing we need is more overpopulation.
Overpopulation is the opposite of our problem. Uncontrolled immigration is the only thing masking a demographic collapse in the US. Fertility rates are at historic lows, far below replacement levels.
It is the same problem in Western Europe, Russia, and Japan.