June 17 (UPI) -- The world population is expected to climb to just under 10 billion over the next three decades -- a rise of nearly 20 percent over the current population, a United Nations report said Monday.
The 2019 World Population Prospects, compiled by the U.N. Department of Economic and Social Affairs' Population Division, projects the global population will reach 9.7 billion by 2050. That would be an increase of 2 billion over the 7.7 billion people in the world today.
The report said within a decade, India will replace China as the country with the world's largest population -- and by the end of the century, the world population will be close to 11 billion.
The study listed the United States as one of nine nations expected to see the largest increases over the next 30 years -- with India, Nigeria, Pakistan, the Democratic Republic of the Congo, Ethiopia, Tanzania, Indonesia and Egypt.
Amy Snover, director of the University of Washington's Climate Impacts Group, said growth, particularly in sub-Saharan Africa, will have a strong impact on climate change.
"Our impact on the climate is tied up with population in lots of different ways -- what resources people are using, how much industrial production is going on, how much energy is needed for heating, cooling and transportation," Snover told NBC News.
"All of these things affect greenhouse gas emissions, so the more people we have and the more resources we use, the harder it will be to cope with the risks and impacts of climate change."
Despite the growth, the report said the world population rate will continue to slow.
The report said 27 countries or areas saw a population decline of at least 1 percent since 2010, due to low fertility rates. That number is expected to nearly double in the next 30 years, with nearly half experiencing a decline of 10 percent or more.
The growth rate has already retreated from 3.2 births per woman in 1990 to 2.5 births this year, and is projected to reach 2.2 by the start of the 2050s -- and 1.9 by 2100.
The median age will rise significantly by the start of the next century, to 41 -- a dramatic increase over the median age of 31 today. It was 24 in 1950.
Life expectancy is having a major impact on the median age. At present, the report said, there are 146 million people on Earth aged 80 or older. By 2100, that figure will skyrocket to 881 million -- an increase of nearly 600 percent.
In its analysis of the U.N. figures, the Pew Research Center said the global population will nearly stop growing by 2100 for the first time in modern history.