At 7.2 billion, the human population is already a serious burden on resources and a threat to the environment and species. Imagine, then, how dire the global situation would be if we were to reach 12 billion, because if the current rate continues, that is what our planet may be facing at the turn of the next century.

According to a new study by the United Nations (UN) and the University of Washington, there is an 80% probability that the world population will reach between 9.6 and 12.3 billion in 2100. That’s around 2 billion higher than previous estimates.

“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,” study author and statistician Adrian Raftery said in a news release. “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.”

As reported in the journal Science, the population projections estimated by the UN were obtained using a field of statistics known as Bayesian statistics in which states of nature are expressed in degrees of belief. To generate their numbers, statisticians combined all available information until 2012 in order to produce superior population predictions compared with previous estimates.

They anticipate that a large proportion of the increase will occur in Africa because of high fertility and birth rates. By the end of this century, it is predicted that the population on this continent will reach a staggering 4 billion, quadrupling the current number. But not all regions will experience such a dramatic increase. Asia, for example, is expected to peak at around 5 billion by 2050, after which it should start to decline. Other continents, such as North America and Europe, are predicted to stay below 1 billion.

Traditionally, researchers use future life expectancy and fertility rates to generate world population predictions. But rather than relying on expert opinion for how those may change over time, this new study used statistics to marry government data and expert forecasts for additional variables such as mortality rates, fertility rates and international migration.

“Earlier projections were strictly based on scenario, so there was no uncertainty,” said first author Patrick Gerland. “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.”

The ongoing growth in human population is a threat to our climate, environment, agricultural resources and various animal species. Furthermore, it will likely exacerbate existing problems such as infectious disease and poverty. If we want to decrease fertility rates, then countries are going to need to focus on providing better access to contraceptives and education, especially for women and girls, which studies have proven to be effective measures.