NEW : World population could surpass 15 billion by the end of the century , the CNN says . In age 25 , the world 's population was 15 billion . People under this century make up 43 % of the current population . Oceania 's population is expected to more than triple this century .
NEW : World population could surpass 15 billion by the end of the century , the U.N. says . In 1927 , the world 's population was 2 billion . People under age 25 make up 43 % of the current population . Africa 's population is expected to more than triple this century .