World population is expected to reach 11 billion by 2100, a new study has found.

Researchers at the University of Washington and the United Nations used modern statistical tools to estimate the number of people inhabiting the world by the end of the 21st century. According to their calculations, population growth will continue throughout this century and will reach a whopping 11 billion by 2100.

Previous estimates had suggested that population growth will slow down in the next few decades and reach around 9 billion people by the start of the next century.

"The consensus over the past 20 years or so was that world population, which is currently around 7 billion, would go up to 9 billion and level off or probably decline," said corresponding author Adrian Raftery, a UW professor of statistics and of sociology. "We found there's a 70 percent probability the world population will not stabilize this century. Population, which had sort of fallen off the world's agenda, remains a very important issue."

An expanding population is expected to put enormous pressure on the already limited food sources and healthcare.

Africa is expected to register a massive population boom in the next few decades. The continent is currently home to about 1 billion people. By 2100, around 3.5 to 5 billion people will inhabit Africa. Previously, the researchers had assumed that lower fertility rates in several African countries will result in a slow population growth. However, some countries - such as Nigeria - have seen a rise in fertility and are expected to see a rapid increase in the number of births throughout this century, The Guardian reported.

Population in Asia will peak at about 5 billion people by 2050 and then see a decline, the study found. Populations in North America, Europe, and Latin America and the Caribbean are projected are expected to stay below the 1 billion mark each.

"Earlier projections were strictly based on scenarios, so there was no uncertainty," Patrick Gerland, a demographer at the U.N., said in a news release. "This work provides a more statistically driven assessment that allows us to quantify the predictions, and offer a confidence interval that could be useful in planning."

According to researchers, two things - contraceptives and education of girls - can help tackle population rise in several countries.

The study is published in the journal Science.