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I've heard people say that we could support far more humans on this planet than we've got right now, given improvements in modern technology. Is this true?

There's a lot more to it than just discussing how many people we could cram onto the planet. What about the quality of human life? What is the role of the human race? Should we keep trying to grow and artificially modify this planet more and more? Should we keep using up many precious resources faster than they can be replenished, leaving little or nothing for our great-grandchildren? Should we keep trying to test the limitations of natural resources, hoping that technology will continue to get ever more efficient? From a biological, ethical, and philosophical standpoint, it is far better for us to stabilize our own growth and preserve wilderness and wildlife. Wouldn't future generations want us to do that?

Are the world's resources really all that finite? For instance, I've heard we've got more than enough food for everyone on this planet.

Human food production capabilities are impressive, with U.N. data indicating almost one ton produced per capita per year, worldwide. However, much of this food never goes directly into the mouths of humans. Much grain, for instance, gets fed to livestock or is used for industrial applications or non-nutritious products like soft drinks. Also, there is a lot of rotting and spoilage, worldwide. More disturbing is the estimate that perhaps half the world's people are malnourished to one degree or another. (Humans need at least 40 different nutrients for good health). Production is not the only challenge. Distribution, warfare, poverty, transportation problems, and corruption play major roles, as well. All these problems have often been exacerbated -- if not caused -- by rapid population growth. These enormous challenges will become even more pronounced as we add more people!

Meanwhile, the environmental impacts of producing food are staggering: huge amounts of soil erosion and salinization (one third of the world's food is produced on irrigated land); deforestation; and resources used for fuel, fertilizer, pesticide, seed, etc. There are pollution and biodiversity problems caused by farm chemicals, as well. About a third of the world's land area is currently devoted to agriculture, but three quarters of that farmland is considered "poor" soil, and much is constantly declining to lower and lower quality. If we add more people, we'll ultimately need more farmland, and there's no more farmland available.

What about water resources? If freshwater supplies become tight, won't we just desalinate salt water from the ocean?

Fresh water, or lack thereof, could be the biggest single resource problem that the human race faces over this century. (The total supply of water in the Earth's biosphere remains constant, but most of it exists as saltwater in the oceans.) The U.N.'s report on global ecosystems (known as PAGE) rates the ecological health of world freshwater resources as "grim," with China, India, the Middle East, and Africa facing particularly severe crises. The southern U.S. will also face increasing shortages. Human activities currently use about half of the world's freshwater flow.

Desalinization technology exists and is currently being used in some Middle East countries; Tampa Bay is considering becoming the first American city to desalinate water. It is expensive, and it uses up many other precious resources (including oil from finite supplies) in the process. And it poses additional transportation costs for areas that are far away from a coastline. The much bigger problem may be damage to biodiversity and ecosystems in coastal estuaries. More humans means ever-greater water demands, not just for household use but for agriculture, industry, and recreation.

Give me a quick rundown on the world energy situation. So what if we run out of petroleum? Won't we just find other energy sources?

Probably. After all, petroleum and cars represented a "solution" to the huge problem of horse manure in big cities a hundred years ago. But one thing's for sure: no energy source will be problem-free when it's used on a scale massive enough to meet the needs of billions and billions of humans. Meanwhile, people want new energy sources to be convenient, economical, safe, and practical. Even when technology accomplishes that, it still takes years for consumers to break away from existing "habits"- just as it's taking years to wean us away from fossil fuels and toward wind, solar, and fuel cells. Meanwhile, people in the developing world burn huge amounts of biomass, mostly wood and crop stalks. More people will mean more demand for energy, regardless of where they are located, and will increase the dilemmas we face. We'll have to artificially modify our ecosystems more and more. The sooner we stabilize our population, the better for our energy options and environmental impact.

Won't sending humans into space solve the population problem on Earth?

The resources it takes to send just eight or nine people into space right now are enormous! It takes massive teams of people and resources to accomplish this feat every several months. But we continue to add over 200,000 people a day to the world's population, net gain! It is highly doubtful that any time soon we will "solve" the world's population growth problem by sending over a million people into space every week!

At present, Earth is our "spaceship" -- and a very beautiful and fertile one at that, but it is one that is under tremendous ecological strain. There seem to be no other planets in our vicinity of space that could provide air, water, soil, and biodiversity in a manner readily useable by humans.