Planet Earth welcomed its 8th billion inhabitant on Tuesday, a remarkable milestone for humanity that is set to propel India to become the world's most populous country next year, surpassing China amid rising global challenges.

The population clock flashed 8,000,000,000 on November 15, with the world having added one billion people in the last 12 years.

"8 billion hopes. 8 billion dreams. 8 billion possibilities. Our planet is now home to 8 billion people," the United Nations Population Fund (UNFPA) tweeted.

"As we become 8 Billion Strong, @DieneKeita explains how a world of 8 billion is a global success story. Together we can build a world that allows 8 billion of us to thrive," it said in another tweet.

The UN described the global population reaching eight billion as a "remarkable milestone" given that the human population numbered under one billion for millennia until around 1800, and that it took more than 100 years to grow from one to two billion.

"The growth of our population is a testament to humanity's achievements, including reductions in poverty and gender inequality, advancements in health care, and expanded access to education," the UNFPA said.

"These have resulted in more women surviving childbirth, more children surviving their early years, and longer, healthier lifespans, decade after decade," it said.

By comparison, the increase of the world's population over the last century has been quite rapid and despite a gradual slowing in the pace of growth, global population is projected to surpass nine billion around 2037 and 10 billion around 2058, according to UN estimates.

World population is projected to reach a peak of around 10.4 billion people during the 2080s and to remain at that level until 2100, said the World Population Prospects 2022 released by the United Nations Department of Economic and Social Affairs, Population Division in July this year.

The year 2023 could well be a landmark year for India as it is projected to overtake China as the world's most populous country with prospects to reap the demographic dividend as the median age of an Indian this year was 28.7 years, compared to 38.4 for

China and 48.6 for Japan against a global value of 30.3 years, according to official data.

The population prospects report had said that India's population stands at 1.412 billion in 2022, compared with China's 1.426 billion. India is projected to have a population of 1.668 billion in 2050, way ahead of China's 1.317 billion people by the middle of the century.

According to UNFPA estimates, 68 per cent of India's population is between 15-64 years old in 2022, while people aged 65 and older were seven per cent of the population.

As per UN estimates, over 27 per cent of the country's population is between the ages of 15-29 years. At 253 million, India is also home to the world's largest adolescent population (10-19 years).

UNFPA has noted that India has its largest ever adolescent and youth population. According to UNFPA projections, India will continue to have one of the youngest populations in the world till 2030 and India is experiencing a demographic window of opportunity, a "youth bulge" that will last till 2025.

For its part, China, which is weighed down by a rapidly increasing ageing population is projected to enter a "severe ageing" phase in 2035 with 400 million people above 60 years, mainly blamed on its decades old one child policy.

China's old age population reached 267 million by last year accounting for 18.9 per cent of the population, Wang Haidong, director of the National Health Commission's Department of Aging and Health said.

It is estimated that the elderly population will top 300 million by 2025 and 400 million by 2035, he said in September according to Chinese official media reports.

The size of China's senior population and its proportion of the total population is expected to peak around 2050, posing huge challenges to the provision of public services and to the national social security system, Wang said.

On the one hand China is rapidly ageing and on the other its population is in decline due to falling birth rates and rising concerns over the future availability of the labour force, the main driver of the economic growth of the Communist nation.

China's population grew by less than half a million-last year to 1.4126 billion as the birth rates fell for the fifth consecutive year, stoking fears of a looming demographic crisis and its adverse impact on the world's 2nd largest economy.

Since last year China allowed Chinese couples to have three children and announced a number of incentives to encourage people to have more children.

The global population milestone comes with both challenges and opportunities, with UN Secretary General Antonio Guterres pointing to world leaders gathered in Bali for the G20 Summit that their action or inaction will determine the future for the eight billion and counting inhabitants of the green planet.

Guterres said the world is facing the most pivotal, precarious moment in generations.

"People everywhere are getting hit from every direction battered by runaway climate change and squeezed by a cost-of-living crisis," the UN chief said.

"Today, as we welcome the eight billionth member of our growing human family, we must think ahead. By 2050, the world's population will be approaching ten billion. Action or inaction by the G20 will determine whether every member of our human family has a chance to live sustainably and peacefully, on a healthy planet," he said.

The UNFPA said that a world of 8 billion people is a "milestone we can celebrate and an occasion to reflect: How can we create a world in which all eight billion of us can thrive?"

It listed eight trends for a world of 8 billion - slowing growth, fewer children, longer lives, people on the move, aging populations, women outliving men, two pandemics and shifting centres.

The UN agency elaborated that after half a century of falling fertility, growth in global population is slowing down.

"Globally, we are getting close to replacement-level fertility - where in the long run a population no longer grows, but maintains equal numbers from generation to generation," it said.

Further, the UNFPA said that across the world people are living longer. In 2019, global life expectancy at birth stood at 72.8 years, up almost nine years since 1990 and is projected to rise to 77.2 years by 2050.

As fertility declines and life expectancy rises, the global population is aging fast and the share of people 65 and over in the population stands at nearly 10 per cent as of 2022 and is projected to rise to 16 per cent by 2050.

The COVID-19 pandemic had an immeasurable impact on mortality and for the regions hardest hit by the earlier HIV/AIDS pandemic, it erased hard won gains in life expectancy.

"COVID19 hit a population already bearing the imprint of HIV/AIDS. Both pandemics have been characterised by unequal access to lifesaving tools and resources," it said.

The UN points out that the growth of the world's population has become increasingly concentrated among the world's poorest countries, exacerbating already entrenched inequalities.

Between now and 2050, almost all of the global increase in the numbers of children and youth and of adults under age 65 will occur in low-income and lower-middle-income countries.

"We face serious challenges as a global community, including the mounting impacts of climate change, ongoing conflicts and forced displacement. To meet them, we need resilient countries and communities. And that means investing in people and making our societies inclusive, so that everyone is afforded a quality of life that allows them to thrive in our changing world," UNFPA said.

The UN agency underlined the need to rethink models of economic growth and development that have led to overconsumption and fuelled violence, exploitation, environmental degradation and climate change, "and we need to ensure that the poorest countries which did not create these problems, yet bear the brunt of their impacts have the resources to build the resilience and well-being of their growing populations."

PTI