(NEXSTAR) — A date circled on the calendar since July is finally upon us: the day the world population is projected to reach 8 billion.

The United Nations (U.N.) released a report in mid-July that predicted Nov. 15 would be the “Day of Eight Billion,” marking a “milestone in human development.”

According to the U.N., which will host events on Tuesday in honor of the Day of Eight Billion, it took the world 12 years to grow its population from 7 to 8 billion. They estimated the world will not reach 9 billion people for another 15 years, “a sign that the overall growth rate of the global population is slowing.”

Improvements to public health, nutrition, personal hygiene, and medicine — as well as “high and persistent levels of fertility in some countries” — are credited for allowing the global population to grow to such a monumental level.

The growth of the world’s population is largely concentrated among the poorest countries, according to the U.N. — roughly 70% of births were in low-income and lower-middle-income countries. Between now and 2037, these countries are predicted to account for more than 90% of growth.

“This is an occasion to celebrate our diversity, recognize our common humanity, and marvel at advancements in health that have extended lifespans and dramatically reduced maternal and child mortality rates,” U.N. Secretary-General Antonio Guterres said in a July statement. “At the same time, it is a reminder of our shared responsibility to care for our planet and a moment to reflect on where we still fall short of our commitments to one another.”

The world’s growing population has, though, contributed to environmental degradation, like climate change and global warming, as well as other inequities. Guterres wrote in a USA Today op-ed last week that, “Unless we bridge the yawning chasm between the global haves and have-nots, we are setting ourselves up for an 8-billion-strong world filled with tensions and mistrust, crisis, and conflict.”

“I never bet against human ingenuity, and I have enormous faith in human solidarity,” he added.

In the same July report, the U.N. projected India would surpass China as the most populous nation in 2023. The United States is expected to remain the third-largest through 2050.

The Associated Press contributed to this report.