I hope the promised study of optimum population growth comes soon. Though declining fertility will require adjustments which are likely to be somewhat (or maybe very) difficult and painful, it is far from obvious to me that the alarmist tone of this piece is justified. We are at more that 7 billion people and have growing evidence that that is way above the long term carrying capacity of the planet. It would, of course be possible to overshoot and end up with a real threat to the survival of the species. However I think that technological change can make it possible to economically survive an environmentally necessary reduction in total population size and that that is what we should be thinking about and planning for.