Removing a birth removes a full lifetime of emissions (all the cars that person would have bought) as well as any future children of that kid; over the long term, the extra emissions from adding a person grow exponentially, while adding a larger car (for a kid that would have existed anyway) is a one-time fixed cost. So, as t->infinity, fewer kids is going to win from a co2 perspective.
So the question is just where the crossover point is (if any; the 8000 fewer kids might already simply offset any larger cars bought within the first year - i don't know). I suppose that requires estimating the number of larger cars bought for third children per year, and comparing to the yearly emissions for people as they age.
So the question is just where the crossover point is (if any; the 8000 fewer kids might already simply offset any larger cars bought within the first year - i don't know). I suppose that requires estimating the number of larger cars bought for third children per year, and comparing to the yearly emissions for people as they age.