BAGHPAT, India (Reuters) - The world's 7 billionth person will be born into a population more aware than ever of the challenges of sustaining life on a crowded planet but no closer to a consensus about what to do about it.
To some demographers the milestone foreshadows turbulent times ahead: nations grappling with rapid urbanisation, environmental degradation and skyrocketing demand for healthcare, education, resources and jobs.
To others, a shrinking population, not overpopulation, could be the longer-term challenge as fertility rates drop and a shrinking workforce is pushed to support social safety for an ageing populace.
"There are parts of the world where the population is shrinking and in those parts of the world, they are worried about productivity, about being able to maintain a critical mass of people," Babatunde Osotimehin, executive director of the U.N. Population Fund, told Reuters.
"Then there are parts of the world where the population is growing rapidly. Many of these countries face challenges in terms of migration, poverty, food security, water management and climate change and we need to call attention to it."
The United Nations says the world's seven billionth baby will be born on October 31.
No-one knows what circumstances the baby will be born into, but India's Uttar Pradesh -- a sugarcane-producing state with a population that combines that of Britain, France and Germany, in a country expected to overtake China as the world's most populous by 2030 -- provides a snapshot of the challenges it could face.
Pinky Pawar, 25, is due to give birth in Uttar Pradesh at the end of the month and is hoping her firstborn will not join the estimated 3 billion people living on less than $2 a day, with little hope of an education or a job.
"I want my child to be successful in life, so I must do my best to make this possible," she said, her hands over her swollen belly as she sat outside her mud and brick home in Sunhaida village.
In Sunhaida, poverty, illiteracy and social prejudice mark a life dominated by the struggle for survival that mirrors millions of others across the world.
With the number of people on earth more than doubling over the last half-century, resources are under more strain than ever before.
First among the short-term worries is how to provide basic necessities for the additional 2-3 billion people expected to be added in the next 50 years.
Water usage is set to increase by 50 percent between 2007 and 2025 in developing nations and 18 percent in developed ones, with much of the increased use in the poorest countries as rising rural populations move to towns and cities.
"The problem is that 97.5 percent of it (water) is salty and ... of the 2.5 percent that's fresh, two-thirds of that is frozen," says Rob Renner, executive director of the Colorado-based Water Research Foundation.
"So there's not a lot of fresh water to deal with in the world."
Nutritious food is in short supply in many parts of the globe. The World Bank says 925 million people are hungry today, partly due to rising food prices since 1995, a succession of economic crises and the lack of access to modern farming techniques and products for poor farmers.
To feed the two billion more mouths predicted by 2050, food production will have to increase by 70 percent, the U.N.'s Food and Agriculture Organisation says.
But just as research, development and expansion of agricultural programs are critical, the public dollars pledged to this effort remain a pittance of what is needed, and are in fact in danger of sharp decline, experts say.
"We have to raise productivity," Robert Thompson, who serves on the International Food & Agricultural Trade Policy Council and is former director of rural development for the World Bank. "I think we can do it all if we invest enough in research. But at the moment we aren't."
Climate change could be the greatest impediment to meeting the food target as rising temperatures and droughts dry out farmlands which are then inundated by intense floods and storms.
The way climate change has been handled offers a window on how tricky it is to tackle global, long-term problems, however.
While it's clear what needs to be done, U.N. climate talks have largely stalled.
"There is a reason why these negotiations are relatively slow," said Wendel Trio, director of Climate Action Network Europe, referring to the economic downturn and arguments between rich and poor nations over carbon cuts.
"But if you compare it to the urgency and the fact that many governments clearly understand the urgency, it is a failure of governments that they can't move forward."
Experts say demographic imbalances will also place serious strains on towns and cities across the world as mostly middle-class blue-collar migrants move from poorer rural areas to richer urban centres.
China's capital Beijing -- with its almost 20 million inhabitants -- is now the world's 13th most populous city, its population almost doubling over the last decade, reflecting a trend mirrored worldwide, particularly in developing nations.
Cities in Africa, Asia and South America are bursting at the seams from migrants seeking better jobs or as farmers flee droughts, floods and other environmental disasters.
In 1950, about 730 million people lived in cities. By 2009, it was nearly 3.5 billion and in four decades it will be 6.3 billion, the U.N. Department of Economic and Social Affairs said in a March 2010 report.
That explosive growth stretches limited resources and infrastructure and places megacities on a collision course with a predicted increase in extreme flooding, storms and rising sea levels from climate change, U.N. Habitat says.
Experts say the lack of coordinated planning is exacerbating the problem.
"Any kind of plan for decentralising the population requires a series of policies that work together," said Wang Jianguo, a senior project officer on urbanisation at the Asian Development Bank's Beijing office.
"If you only have a population policy without an employment policy, without an industry development policy, education, medical policy, it won't work."
One important policy tool to manage a growing population is to give women access to family planning, experts say, adding that 215 million women worldwide want it but do not get it.
Access to education is also important as it motivates women to reduce their fertility and improve their children's health.
A lack of such education has meant that while the overall populations continue to rise in countries such as China and India, the number of women is falling because of a preference for boys leading to deliberate abortions of female babies.
The world is also seeing a demographic anomaly: a declining population in some richer countries has led to an imbalance between the working population and retirees who need expensive social safety nets.
The global fertility rate -- the number of children born per couple -- is around 2.5, but in richer countries this number has already nosedived.
And while exact predictions vary, most suggest the global population will peak at around 9 billion around 2070 and then start to fall, perhaps very fast.
"We thought that overpopulation was going to force humanity to expand outward to the stars," says Jack Goldstone, professor of social science and a leading demographics expert at Washington's George Mason University.
"That doesn't look like the problem at all. And the policy framework isn't set up at all to handle these longer-term issues."
Additional reporting by Sui-Lee Wee and Michael Martina in Beijing, Deborah Zabarenko in Washington, Peter Apps in London, Julie Steenhuysen in Chicago, David Fogarty in Singapore and Carey Gillam in Kansas City; Editing by Sonya Hepinstall