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From "The Columbus Dispatch" (February 13, 2007)


Scientists debate how much population the world can sustain

by Mike Lafferty

The streets of Dhaka, Bangladesh, teemed with people in 1994.  Thirteen years later, Bangladesh has a population of nearly 150 million people.

In the days of sailing ships, sailors used to leave goats on islands as they passed to ensure fresh meat on return trips. It worked too well. The animals bred faster than the sailors could eat them, and from the Channel Islands off California to the Seychelles in Indian Ocean, goats ate all the vegetation and began to  starve. The goats also screwed up the environment so that native species couldn’t survive, either," said John Wenzel, director the Ohio State University Museum of Biological Diversity. For example, the goats stripped away plants’ low-growing leaves so that tortoises couldn’t find enough to eat.

Some biologists say the lesson of the goat applies to humans and point out how our "island" has suffered.

There is air and water pollution, falling water tables, climate change and rampant extinction of wild plants and animals, to name a few problems.

Two weeks ago, the Intergovernmental Panel on Climate Change released its report blaming humans for increased temperatures, melting glaciers and rising seas.

Too many people, the group said, are burning too many fossil fuels.

"With global warming, we’ve been able to create this problem in the first place because we’ve had virtually free energy in the form of fossil fuels," said Ohio State University ecologist Tom Waite.

Climate change, Waite and others say, is a sign that we are exceeding the number of people Earth can sustain.

Every year, at least 91 million humans are born in excess of those who die. That’s 1 billion people every 11 years.

Some, however, argue that we are adept at adapting, and point to increased agricultural production and medical advances that fend off disease.

Right now, Earth’s carrying capacity is thought to be somewhere in the range of 4 billion to 5 billion people.

There are 6.5 billion of us.

In biology, the carrying capacity usually refers to the number of animals a given area can support with adequate food, shelter and territory or the space to reproduce.

Duke University ecologist Stuart Pimm said half of the world’s population has little access to medicine, electricity, safe water and reliable food supplies.

"When you get to the nitty-gritty of the term, some animals are more equal than others. Some countries are a lot more equal than others," Pimm said.

No one is sure what the magic number is.

"You might have 50 billion, but the quality of life might not be terribly pleasing," Pimm said. "Rabbits are the same way. The key word is support."

How many people can Franklin County support?

If the 1.3 million residents of Franklin County had to live on the resources the county could provide, Waite figures, only about 100,000 would live here.

"We’re oblivious to that number because we happily import the vast majority of our needs," Waite said. "If you put a bubble over the whole state of Ohio, you could support about 1 million people."

The United States has the resources to sustain less than half of its current population of 300 million, according to ecologist Paul Ehrlich, who first called attention to potential population problems in 1968 with his book, The Population Bomb.

Waite and other ecologists increasingly think of the idea of carrying capacity in terms of an ecological "footprint," the amount of land on Earth that it takes to support a group of people.

Americans, who make up 5 percent of the world’s population, use 25 percent of its resources and cast a large footprint.

"Ohio’s footprint is like 11 times the state of Ohio," Waite said.

The average American’s footprint is about 22 acres. By far, the largest component is energy, according to Waite. In contrast, the average citizen of India has a footprint one-sixteenth that size.

If all 6 billion people were to share the world’s resources equally, Americans would have to reduce consumption by 80 percent for each of us to have a footprint of about 4.4 acres.

"My footprint is magically (4.2 acres) because I don’t own a car," Waite said.

He and his wife bike to work.

A photovoltaic system on the roof of the Waites’ home produces more electricity than the couple usually uses. The surplus goes onto the electricity grid. The couple grow many of their own vegetables.

But Waite’s footprint grows when he arrives on campus or has to rent a car to attend a meeting out of town.

"The moment I show up at work, I suddenly violate the fair Earth share and I become unsustainable," Waite said.

In fact, he estimates that his footprint quadruples.

Carrying capacity and footprint are tied to the global economy, which has quadrupled since the world’s population doubled, Waite said.

That leads to a fear that slowing population growth might not ultimately curb greenhouse gas production if more people achieve Westernstyle lifestyles, said Barry Rabe, a University of Michigan political scientist who studies environmental issues.

India and China are developing rapidly and have already affected climate change.

China is opening an average of one coal-fired power plant a week to meet electricity demand. The power plants emit carbon dioxide, a greenhouse gas.

"Everyone in China wants two things: their own apartment and their own car," Pimm said. "That change is going to have a massive effect on the planet."

Lester Brown, president of the Earth Policy Institute, said the sustainability question is a loaded one.

"People ask me how many people the Earth can sustain. I usually respond that it depends on whether you want to live like an Indian or an American."

For example, farmers worldwide grow about 2 billion tons of grain every year. Each American consumes an average of 1,760 pounds annually, mainly because of the grains used to feed farm animals. If everyone on the planet consumed that much grain, Brown said, Earth would support about 2.5 billion people.

But in India, people consume about 440 pounds each. If everyone else in the world did likewise, the world’s grain would support about 10 billion people.

Population, water and food are tied together. Growing 1 ton of grain requires 1,000 tons of water.

There already are water shortages in Africa, Asia and the Middle East. As water is diverted from agriculture to support growing urban populations, more grain must be imported.

Alternative energy, touted as a possible solution to burning fossil fuels that generate greenhouse gases, also adds a factor to the food equation.

Soybeans are increasingly in demand for biodiesel. And ethanol production now vies with food for corn. Brown estimates that by 2008, half of the U.S. corn crop will go to ethanol.

"Seventy percent of all corn imports in the world come from the U.S., so what happens to U.S. corn crops affects a lot of countries," he said.

Waite said this competition for energy and food will change the landscape.

"If we were to replace our reliance on fossil fuels and instead grow fuel plants, that would require setting aside lots of land to produce ethanol," Waite said.

"We don’t have enough land worldwide to meet those demands."

Demand for food, fuel and materials already consumes more trees and crops than are being grown worldwide.

Waite compares the issue to a bank account.

Humans, he said, are already drawing on capital rather than interest, and once that is exhausted, they will find Mother Nature reluctant to make a loan.



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