The world's population will hit 7 billion this year, raising concerns about the economic and environmental consequences associated with continued growth, according to an article by a Harvard School of Public Health professor.

In a paper published in Friday's edition of the journal Science, David E. Bloom, the chair of the Department of Global Health and Population, explored the global implications of the human population surpassing 7 billion, a milestone the United Nations has projected will occur on Oct. 31.

The exploding population increase will take the greatest toll on developing regions of the world, Bloom said. By 2050, according to a U.N. estimate, worldwide population will rise to approximately 9.3 billion people. 97 percent of that increase will occur in less developed nations.

"The world’s demographic center of gravity will continue to shift from the more to the less developed countries and especially to the least developed countries, many of which will face unprecedented and daunting challenges related to the supply and distribution of food, water, housing, and energy," Bloom wrote in the article.

Over the next 40 years, the population increase in Africa alone will make up 49 percent of population growth worldwide.

In more developed countries, however, population growth will slow over the next half-century. As life expectancy increases, birth rates continue to drop, and as the population ages, the proportion of retired adults will increase relative to those of working age.

More developed nations will face their own host of demographic shift problems, including supporting this aging population whose reliance on social welfare programs may outstrip the ability of the workforce to finance these programs.

Adolescents and young adults, aged 15 to 24, currently outnumber those 60 and above by 54 percent, Bloom wrote. After 2025, however, the older population will overtake the younger, setting off a gigantic demographic shift. While those aged 60 and above make up 11 percent of the world’s population today, by 2050, they will comprise 22 percent.

“Although the issues immediately confronting developing countries are different from those facing the rich countries, in a globalized world demographic challenges anywhere are demographic challenges everywhere,” Bloom said in a press release.

Worldwide population reached 1 billion in 1800, 2 billion in 1927, and 3 billion in 1960. Since then, population has increased by 1 billion approximately every 13 years.

Depending on changes in birth rate, the population in 2100 could range from 6.2 to 15.8 billion people, according to U.N. estimates.

“We have to tackle some tough issues ranging from the unmet need for contraception among hundreds of millions of women and the huge knowledge-action gaps we see in the area of child survival, to the reform of retirement policy and the development of global immigration policy,” Bloom said in the press release. “It’s just plain irresponsible to sit by idly while humankind experiences full force the perils of demographic change.”

—Staff writer Leanna B. Ehrlich can be reached at lehrlich@college.harvard.edu.