Our population is expected to hit 7 billion soon, leading some to wonder if we have already passed our planet's carrying capacity.

It took thousands of years for humans to first establish a firm presence here. Then, our population began doubling very quickly. If you are a baby boomer and were born in 1945, you saw the population double within your early life - to 2.3 billion - then double again around 2003. If you live out your life expectancy, you will see the population more than triple in the span of one lifetime, to 7 billion by 2012.

Looking at Earth as a whole, we have about 22 billion acres of usable land. This contains about 3.3 billion acres of farmland, 8.4 billion acres of pastureland and 10.1 billion acres of forestland. Not all of the land is fertile, which will determine its ability to produce food. We also must share this land with other species already dependent upon the land for survival.

According to "A Walk Through Time" by Dr. Sidney Liebes, if the earth were the size of a ball that you could hold in your hand, the amount of usable farmland would look like a tiny speck of dirt by comparison. Additionally, all the drinkable water would look like a tiny water droplet, while the breathable atmosphere would be a thin coating of shellac.

Our ecological footprint, which measures how much land it takes to feed, clothe and shelter a typical American, is about 9.6 global hectares, compared to the available 1.8 global hectares of usable land that should be used if you divided the land up fairly (according to Wikipedia). If everyone used resources and land the way we Americans do, we would need three more planets to sustain our population.

Estimates of the earth's carrying capacity vary according to which population you are measuring, since some populations live more frugally than others. Some scientists say that not only are we living beyond earth's carrying capacity, but we are also destroying future generations' ability to live within the earth's means. We are literally emptying the earth's bank account rather than living off the interest as our ancestors have done. We're leaving a "balance due" for future generations.

British geographer Ernst George Ravenstein is credited with first estimating the carrying capacity of the earth to around 6 billion. Presently, at 6.5 billion, at least a billion people don't receive enough food to carry out a day's work. Even through Ravenstein was operating on statistics from last century, he hit fairly close to home.

Before Ravenstein, the English clergyman Thomas Robert Malthus argued that the human population always increases more rapidly than food supplies and that humans are condemned to breed to the point of misery and starvation. The 200 years since his essay was first published have proven him wrong. We can artificially increase food production above birth rates, and even decline in numbers in the presence of plenty.

The World Hunger Program at Brown University estimated "the world could sustain either 5.5 billion vegetarians and 3.7 billion people who get 15 percent of their calories from animal products (as in much of South America), or it could sustain 2.8 billion people who derive 25 percent of their calories from animal products (as in the wealthiest countries)." That was based on 1992 levels of food production and an equal distribution of food.

Clearly we have passed all sustainable estimates and are now entering the "borrowed time" area of the population chart. In order to provide the projected 9 billion population in 2050 with 2,100 calories per day (what food aid agencies declare as the minimum caloric intake), we would have to double our global agricultural production. Humans have already plowed over most of the usable farmland on the planet, and there is a limit to any field's fertility. Could Malthus be right after all?

This is not a new chapter in human history. We have faced starvation before, and triumphed. According to environmental analyst Lester Brown, "in the 15th century, Icelanders realized that overgrazing of their grasslands was leading to soil erosion. Farmers then calculated how many sheep the land could sustain and allocated quotas among themselves, thus preserving their grasslands, and a wool industry that thrives today."

Here are some steps you can take to reduce your ecological footprint:

- Measure your ecological footprint at www.myfootprint.org

- Walk, bike or share a ride instead of driving or flying

- Have a home energy audit and increase your home's efficiency

- Adopt energy-saving habits and use "low tech" clotheslines and curtains

- Eat local, in season, and organic

- Eat less meat

- Invest in a greener home instead of a bigger home

- Buy less, reuse more

- Have smaller families and support zero-population growth

Shawn Dell Joyce is a sustainable artist and writer who lives in a green home in the Mid-Hudson region of New York.

© Copley News Service

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