The world’s human population may stop growing sooner than expected, according to a study published yesterday in the journal Nature. Using a statistical computer model that takes into account uncertainties like birth rates, migration, and mortality, the study says there is an 85 percent chance that the world’s population will dip to 8.4 billion in 2100, after peaking at 9 billion in 2070. The study says the populations of north and sub-Saharan Africa are likely to double, while populations in parts of the developed world will probably decline.