How exactly does one go from "the population has grown by 1 billion in the last 12 years, and again in the 12 years before that" to "the population will grow by 2 billion in the next 34 years". Is there any real evidence that our rate of growth is decreasing?
An increase in life expectancy and a decline in birth rates means that population increases in the near future will more and more be in the form of people living longer, rather than increases in the number of new people. After a while the decline in birth rates will catch up, and population will decline. Japan and Europe are furthest along this curve, but rest of world looks poised to follow.