The majority of world population growth by 2050 is expected to occur in developing nations despite higher HIV prevalence and infant mortality rates than those of developed nations, according to the annual Population Reference Bureau report released on Tuesday. The world's population is expected to rise 45% to nearly 9.3 billion by 2050, including a 4% increase in the population of developed countries to more than 1.2 billion and a 55% increase in developing nations' populations to more than eight billion.