 Some believe that the UN is overestimating population growth, and that if anything, rather than an overpopulation problem, we might have a de-population problem later in this century. This is what Darrell Bricker and John Ibbison argue in their book Empty Planet, in which they essentially make the case that what is more likely to happen is closer to the UN's low variance scenario, and that it may be coming faster than the UN thinks.