David Gray / Reuters

A garbage collector walks atop a massive pile of garbage at the Bloemendhal dump in central Colombo, Sri Lanka, on April 23, 2009.

Will the sheer scale of 7 billion people living on the planet doom human existence to extinction?

Not likely, many scientists say, but they do worry about how many people a disturbed and soiled Earth will support.

The United Nations Population Fund predicts not only that the planet’s population will reach 7 billion by Oct. 31, but another billion will be here by 2025, and the total will reach 10 billion before the end of the century.

China Daily via Reuters

A worker cleans away dead fish at a lake in Wuhan, central China's Hubei province, on July 11, 2007. More than 110,000 pounds of fish died due to pollution and hot weather, local media reported.

Beawiharta Beawiharta / Reuters

Deforestation is evident on Indonesia's Sumatra island on Aug. 5, 2010. Indonesia, like Brazil, is on the front line of efforts to curb deforestation, a major contributor to mankind's greenhouse gas emissions that scientists blame for heating up the planet.

All those people will need water, food, clothing, shelter, energy – all of which take resources to create or distribute and which can foul the environment as they’re processed and used up.

In 1798, when the world’s population was close to 1 billion, British-born economist Thomas Malthus wrote, "The power of population is so superior to the power of the Earth to produce subsistence for man, that premature death must in some shape or other visit the human race."

Malthus did not take into account the then-coming industrial age and people’s inventions and ingenuity that meant more efficient use of Earth’s resources. However, population growth could be catching up to problems it creates.

Reinhard Krause / Reuters

Cars jam a Beijing road on Jan. 15, 2008. More than 400,000 new cars, or more than 1,000 a day, hit the roads in China's capital in 2006, state media said.

Asahi Shimbun / Reuters

Medical staff use a Geiger counter to screen a woman for possible radiation exposure at a public welfare center in Hitachi City, Japan, on March 16, 2011. The woman tested negative for radiation exposure after she was evacuated from an area within 12.4 miles of the Fukushima Daiichi nuclear plant, which leaked radiation when it was badly damaged by a massive earthquake and tsunami on March 11.

Modern scientists warn that the Earth’s climate is warming and access to clean water is dwindling. Oil spills contaminate beaches and oceans; poisons leach from dumped waste into soil and water; the burning of fossil fuels pumps more carbon dioxide into the atmosphere than it can absorb.

New energy sources will be needed as known sources of fossil fuels are depleted or remain locked away.

Reuters

A man works at the site of a rare earth metals mine at Nancheng county, China, on Oct. 20, 2010. China reportedly produced 118,900 metric tons of rare earth in 2010, well above the 89,200 metric ton official production quota. The production figure exceeded 96 percent of global output, The Wall Street Journal reported .

Pawel Kopczynski / Reuters

Steam emerges from the cooling towers of Vattenfall's Jaenschwalde brown coal power station near Cottbus, Germany, on Dec. 2, 2009.

"Hunger and poverty are challenges we all face together - we must act now," said Pierre Ferrari, president of Heifer International, which provides cows, goats, water buffalo and other livestock to thousands of people in more than 50 countries. The charity focuses on helping the poor become self-sufficient and urges the people it helps to go on to train others.

"Our global agricultural system can feed 7 billion people today," Ferrari said. "It is a matter of equity and distribution."

"The real issue to be faced is the next 30 years when another 2 billion people will be with us," he said. "It is forecasted that the global food supply will need to double to meet the needs of the global population.  The small holder farmer (650 million of them) produces 70 percent of the world food today."

Heifer is an example of a non-government organization that works to improve agricultural productivity.

But will such efforts be enough?

"The constraints of the biosphere are fixed," Harvard University sociobiologist Edward O. Wilson wrote in his 2002 book, "The Future of Life."

As reported by Life’s Little Mysteries, Wilson predicted the Earth’s resources could be stretched to support a population of 10 billion, just about where UN population estimators say growth will level out by the end of the century.

- msnbc.com editors Natalia Jimenez and Jim Gold, with wire service reports.

See more posts and images related to the seven billion population milestone

Michael B. Watkins/U.S. Navy via Reuters

Oil is seen on the surface of the Gulf of Mexico in an aerial view of the Deepwater Horizon oil spill off the coast of Mobile, Alabama, on May 6, 2010.