From you own link: "The United Nations Population Division projects world population to peak at over 10 billion at the end of the 21st century, but Sanjeev San

From you own link: "The United Nations Population Division projects world population to peak at over 10 billion at the end of the 21st century, but Sanjeev Sanyal has argued that global fertility will fall below the replacement rate in the 2020s and that world population will peak below 9 billion by 2050, followed by a long decline. A 2014 study in Science concludes that the global population will reach 11 billion by 2100, with a 70% chance of continued growth into the 22nd century." So clearly there is disagreement between those two. Using the 2014 study, there would be an increase in the current population(~7 billion) by greater than 50% and continued growth for another centruy.