The United Nations has predicted the global population will reach seven billion this year, and climb to nine billion by 2050, "with almost all of the growth occurring in poor countries, particularly Africa and South Asia," said John Bongaarts of the non-profit Population Council.

To feed all those mouths, "we will need to produce as much food in the next 40 years as we have in the last 8,000," said Jason Clay of the World Wildlife Fund at the annual meeting of the American Association for the Advancement of Science (AAAS).

"By 2050 we will not have a planet left that is recognizable" if current trends continue, Clay said.

The swelling population will exacerbate problems, such as resource depletion, said John Casterline, director of the Initiative in Population Research at Ohio State University.

But incomes are also expected to rise over the next 40 years -- tripling globally and quintupling in developing nations -- and add more strain to global food supplies.

People tend to move up the food chain as their incomes rise, consuming more meat than they might have when they made less money, the experts said.

It takes around seven pounds (3.4 kilograms) of grain to produce a pound of meat, and around three to four pounds of grain to produce a pound of cheese or eggs, experts told AFP.

"More people, more money, more consumption, but the same planet," Clay told AFP, urging scientists and governments to start making changes now to how food is produced.

Population experts, meanwhile, called for more funding for family planning programs to help control the growth in the number of humans, especially in developing nations.

"For 20 years, there's been very little investment in family planning, but there's a return of interest now, partly because of the environmental factors like global warming and food prices," said Bongaarts.

"We want to minimize population growth, and the only viable way to do that is through more effective family planning," said Casterline.

earlier related report
World Phosphorus Use Crosses Critical Threshold
Madison WI (SPX) Feb 17, 2011 - Recalculating the global use of phosphorus, a fertilizer linchpin of modern agriculture, a team of researchers warns that the world's stocks may soon be in short supply and that overuse in the industrialized world has become a leading cause of the pollution of lakes, rivers and streams.

Writing in the Feb. 14 edition of the journal Environmental Research Letters, Stephen Carpenter of the University of Wisconsin-Madison and Elena Bennett of McGill University report that the human use of phosphorus, primarily in the industrialized world, is causing the widespread eutrophication of fresh surface water. What's more, the minable global stocks of phosphorus are concentrated in just a few countries and are in decline, posing the risk of global shortages within the next 20 years.

"There is a finite amount of phosphorus in the world," says Carpenter, a UW-Madison professor of limnology and one of the world's leading authorities on lakes and streams. "This is a material that's becoming more rare and we need to use it more efficiently."

Phosphorus is an essential element for life. Living organisms, including humans, have small amounts and the element is crucial for driving the energetic processes of cells. In agriculture, phosphorus mined from ancient marine deposits is widely used to boost crop yields. The element also has other industrial uses.

But excess phosphorus from fertilizer that washes from farm fields and suburban lawns into lakes and streams is the primary cause of the algae blooms that throw freshwater ecosystems out of kilter and degrade water quality. Phosphorus pollution poses a risk to fish and other aquatic life as well as to the animals and humans who depend on clean fresh water. In some instances, excess phosphorus sparks blooms of toxic algae, which pose a direct threat to human and animal life.

"If you have too much phosphorus, you get eutrophication," explains Carpenter of the cycle of excessive plant and algae growth that significantly degrades bodies of fresh water. "Phosphorus stimulates the growth of algae and weeds near shore and some of the algae can contain cyanobacteria, which are toxic. You lose fish. You lose water quality for drinking."

The fertilizer-fueled algae blooms themselves amplify the problem as the algae die and release accumulated phosphorus back into the water.

Carpenter and Bennett write in their Environmental Research Letters report that the "planetary boundary for freshwater eutrophication has been crossed while potential boundaries for ocean anoxic events and depletion of phosphate rock reserves loom in the future."

Complicating the problem, says Carpenter, is the fact that excess phosphorus in the environment is a problem primarily in the industrialized world, mainly Europe, North America and parts of Asia. In other parts of the world, notably Africa and Australia, soils are phosphorus poor, creating a stark imbalance. Ironically, soils in places like North America, where fertilizers with phosphorus are most commonly applied, are already loaded with the element.

"Some soils have plenty of phosphorus, and some soils do not and you need to add phosphorus to grow crops on them," Carpenter notes. "It's this patchiness that makes the problem tricky."

Bennett and Carpenter argue that agricultural practices to better conserve phosphate within agricultural ecosystems are necessary to avert the widespread pollution of surface waters. Phosphorus from parts of the world where the element is abundant, they say, can be moved to phosphorus deficient regions of the world by extracting phosphorus from manure, for example, using manure digesters.

Deposits of phosphate, the form of the element that is mined for agriculture and other purposes, take many millions of years to form. The nations with the largest reserves of the element are the United States, China and Morocco.

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