The Exploding Human Population
      Every second that ticks away on your wristwatch marks the addition of three new residents to world population. In a single day, this seemingly modest increase results in a  surge in the global human population of one quarter of a million people!  In a year's time, this daily growth results in the addition of nearly 90 million people.
      The impacts of population are two-fold. They stem from its current population size, 6 billion strong, and the continuing rapid rate of growth. The effects of these two factors are many and varied. They occur in social, economic, and environmental realms.  Not all impacts are obvious to the casual observer and many are hotly debated. To understand the population dilemma and ways to solve it, we first take a glimpse back in time to discern the reason for the upsurge in human numbers. 
 

What Caused the Rapid Growth?
      The growth in human population is a relatively recent phenomenon in human history.  Homo sapiens emerged about 400,000 years ago.  But as Figure 1 clearly shows, world population remained quite small for most of our species' long evolutionary journey.  In fact, it was not until the past 150 years that the human population underwent its dramatic rise.  During this time, the population increased from 1 billion to its present size of nearly 6 billion.
      The recent increase in human numbers results from several factors, notably the Agricultural and Industrial revolutions.  Early in human history, in the days of hunters and gatherers, people lived nomadic existences.  Life was fairly short. Numbers remained stable because of high mortality.  Then, about 10,000 to 12,000 years ago people began to eke out a living by growing their own food.  Simple wooden tools were often used to grow crops.
      The cultivation of crops aided by primitive tools and irrigation systems made it possible for more people to live off the land.  But early agricultural successes were modest compared to those that took place during the Industrial revolution, which began in the 1700s in Europe and the 1800s in North America.  This period saw many new developments that spurred population growth.  Metal plows, for example, developed in factories of the industrializing nations  made it possible for farmers to grow far more food than ever before. More advanced systems of irrigation also aided farmers in food production.  Gas- powered tractors, combines, and other farm machines greatly expanded the world's grain production and gave the human population its fuel for unprecedented growth.
     The Industrial revolution also ushered in the age of chemistry.  With it came new drugs to combat disease and illness.  These chemical weapons helped reduce devastating epidemics of infectious disease that claimed the lives of millions of people.
       Yet another advance in this long march toward numerical dominance was the advent of sanitation and water treatment.  Treating sewage to kill potentially harmful microorganisms before it was released into surface waters from which people got their drinking water, and purifying drinking water lowered one's chances of contracting infectious disease.  The death rate plummeted.  More children than ever survived to adulthood.  They, in turn, married and had children of their own.  The human population began to grow out of control.
      Growth has continued largely unabated for a century and a half throughout much of the world.  Fortunately, growth rates in the industrial nations eventually slowed.  This came about as families voluntarily reduced their size.  Today, the more developed countries (MDCs) house only about 20% of the world's population — or approximately 1.2 billion people — and are growing at a relatively slow rate of 0.3% per year.  This slow rate of growth translates into a population doubling time of 265 years.
      Growth continues at a rapid pace in the less developed nations (LDCs) of the world — the poor countries of Asia, Africa, and Latin America.  Although death rates have fallen, birth rates remain high.  Consequently, the LDCs currently house about 80% of the world's population — or about 4.6 billion people — and are growing six times faster than the populations of the MDCs.  At their current rate of growth, just under 2% per year, their populations could theoretically double in just 35 years, reaching 9.2 billion by 2030.
      Many people take these statistics to mean that the world population crisis is largely a problem of the LDCs.  Surely, experts agree, population growth in the LDCs represents an enormous challenge with grave consequences, but growth in numbers is equally important in the wealthier nations of the world — perhaps even more so.
      The reason for this high level of concern for what appears to be relatively slow growth in a small segment of the world population boils down to one factor: level of affluence.  The higher living standards of the MDCs results in an extraordinary level of resource consumption.  This, in turn, places incredible demands on the Earth's natural systems.
       According to several estimates, the average American consumer uses 20 to 40 times more resources in a given day than a resident of India.  Driving your car a mile to the convenience store to pick up a six-pack of cola uses as much energy as an average resident of a LDC uses in an entire day to meet all of her needs!  Each child born into a more developed nation will have a far greater impact on the planet than a child born into a family in Bangladesh or China.  Because of their disproportionate resource demand, the 10 million new residents of the MDCs nations that join the world population each year actually have about the same environmental impact as 200 to 400 million residents in the poorer, non-industrial nations of the world. Because of this, population growth in the affluent nations is therefore as much an issue of concern as is the growth in the poorer nations of the world. 

Meeting Basic Needs In a Growing World
       Rapid population growth creates many challenges for all nations rich and poor.  Currently, the United Nations Food and Agriculture Association estimates that over 800 million people go to bed hungry each night — one seventh of the world's population.  By various estimates, 12 million people die each year because of hunger and malnutrition and diseases whose symptoms are worsened by them.
      Although the number of people receiving inadequate amounts of food has declined in recent years, many people are suffering.  If many countries cannot adequately feed their existing populations, how will they fill the needs of the millions of newcomers arriving in the next decades?
       But people do not live by bread alone.  They require water, shelter, and clothing.  They require health care, sanitation, education, and transportation.  In 1994, the World Health Organization (WHO) of the United Nations estimated that 940 million people lack access to safe water and over 1,700 million people worldwide lack adequate sanitation.   WHO further noted that most urban centers in Africa and Asia have no sewage systems at all, including many cities with populations over 1 million.  Unfortunately, this situation is not improving.   From 1960 to 1990, population growth has outpaced the provision of safe drinking water and sanitation services.   In developing countries, unsafe drinking water now results in the death of over 25 million people annually.
       Housing is also inadequate.  In Cairo, Egypt, poverty and housing shortages are so severe that several hundred thousand people currently live in a giant graveyard on the outskirts of the city.  These unfortunate individuals live in shelters made of cardboard and other materials.  Many of those inhabitants of Cairo who are fortunate enough to afford and find housing live in tiny, dirty apartments.  One third of these dwellings don't have toilets.
       In Calcutta, India, conditions are even worse.  Approximately 70% of the city's residents live below the poverty line.  Many occupy slum dwellings without running water.  Approximately half of the dwellings lack indoor toilets.  Twenty-five families often share a single outdoor water tap to acquire the water they need to drink and bathe.  An estimated 600,000 residents of this city have no homes.  They roam the streets, begging and stealing.  Many sleep in alleyways strewn with garbage and human waste.
       Even in the more well-to-do cities, like Shanghai, China, housing leaves much to be desired.  In this city of more than 12 million people, living space is severely limited.  The average resident has about as much living space as an average American bathroom.
       This discussion is not meant to imply that the problems of overpopulation are only manifest in poorer nations.  As many a reader can attest, cities in the developed nations of the world like New York City, Los Angeles, Miami, and Chicago house millions of destitute people in crime-infested slums.  Streets and alleyways are often strewn with trash.  Drug use and crime abound. Given the rapid growth of the world population and the inadequate state of many services worldwide, the already-intolerable conditions in crowded urban areas are only bound to worsen.
       Population growth and crowding in cities also spawn a host of social problems such as crime and civil unrest.  In a number of countries in Africa, burgeoning urban populations and a host of other factors have resulted in anarchy in several nations that threatens to spread throughout the continent.  In countries of the south Sahel, the region south of the Sahara, police and government sponsored armies enjoy a tenuous hold on cities during the day.  At night, however, the streets become the exclusive domain of rival gangs.
       Crime, social strife, food shortages, and poverty in Africa have spawned a massive movement of refugees both within nations and between nations.  People seeking safety from intolerable living conditions often swamp refugee camps where they are marginally cared for while war rages between rival groups in their homeland.   Currently, the best available estimates put the number of refugees who have fled their countries because of violence, political upheaval, inadequate food, and other related factors at 19 million. Another 25 million or so have fled to other parts of their own nations.

Fouling Our Nest
       The population explosion has profound influences on the quality of the environment — the air, water, and land.  The impacts can be felt locally, regionally, and, with growing frequency, globally.  The changes in the environment are cause for grave concern.
       Although many people take nature for granted, natural systems are extremely important to our lives. Ecosystems are quite literally the life support systems of the planet.  They provide air and water.  They provide food in abundance.  They also provide a host of free services vital to our long-term prosperity and, some say, our survival on the planet.  Wetlands along rivers, for example, absorb rainwater and reduce the frequency and severity of flooding.  One scientist determined that the devastating floods in 1993 along the course of the mighty Mississippi River could have been avoided had even a modest portion of the original wetlands been left intact.
       Wetlands also help filter impurities from water and recharge aquifers, that is, groundwater supplies.  Coastal wetlands are a vital habitat of many commercially important fish and shellfish.  Chances are the fish you recently ate spent some part of its life cycle in a coastal wetland.
       Forests also provide additional services.  They help hold soil in place and thus reduce soil erosion, keeping streams clean.  Trees in forests replenish atmospheric oxygen needed by all animals.  And, they absorb carbon dioxide, a waste product of cellular energy production in plants and animals.  As such, forests are an essential part of the global cycling of oxygen and carbon dioxide.  But because carbon dioxide has profound influences on global temperature, intact forests are an important determinant in maintaining global climate.
       The Earth provides many resources that are vital to our economy.  Take a moment to look around you.  Everything in your immediate vicinity — from the computer on your desk to the coffee maker on your kitchen counter — comes from a mine, forest, grassland, or aquatic ecosystem.
       Natural systems are also an enormous "sink" for wastes.  They often absorb waste products, even toxic ones, and render them harmless.  Recognizing the importance of the environment to our well being, some economists and ecologists have begun to refer to the natural world as the biological infrastructure or "infra-infrastructure" of  human society.  Just as their importance is being more widely recognized, growing evidence shows that growth of the human population, which results in ever-rising demand for natural resources and ever-increasing levels of waste, is severely undermining the condition of many of the parts of our life support system. 

Imperiled Surface Waters
       Surface waters — streams, rivers, lakes, and ponds — have been adversely affected by human population growth in many ways.  Farming and timber harvesting, which increase to meet the needs of a growing population, for example, reduce ground cover and increase soil erosion.  Soil washed from these lands enters surface waters where it increases turbidity and reduces sunlight penetration.  This, in turn, decreases photosynthesis by aquatic plants, which reduces dissolved oxygen concentrations killing sensitive aquatic species.  Water pollution from factories also alters water chemistry and makes conditions hazardous for some species.  Physical changes to rivers themselves such as dam construction and dredging also irrevocably alter aquatic habitats and can eliminate many species.  One victim of the changes in water quality is the freshwater mussel.
       Freshwater mussels are molluscs like clams and oysters that feed on tiny microorganisms called plankton. Mussels filter the water they live in and consequently help to maintain desirable water quality essential for the survival of other species.  Scientists estimate that when the Europeans arrived in North America 300 species inhabited the streams, rivers, and lakes in the Eastern United States.  Since 1900, 30 of these species have vanished.  Another 200 are endangered (close to extinction) or threatened (suffering declining numbers that could lead to a change in their status to endangered).  Only about 75 of the original 300 species are considered to be stable.
       Freshwater systems are extremely rich in life forms and disproportionately imperiled by population growth for two reasons.  First, sixty percent of the world's population lives within one kilometer (.6 miles) of a lake, river, stream, pond, or ocean.  Second, virtually all human activity that occurs in a river's watershed affects water quality and impacts typically rise as the population swells. 

Polluting the Air We Breathe
       Yet another problem that stems from population growth is air pollution.  All nations of the world suffer from air pollution, sometimes choking levels.  Air pollution arises from factories and power plants.  It is produced in huge amounts from many tiny sources, too, such as the millions of coal-burning stoves in the shanties of China's peasant farmers who use this fuel to cook their food.  Air pollution is released from the world's ever-growing fleet of automobiles, trucks, buses, planes, and trains.  Although air pollution comes from natural sources like volcanoes and swamps, human sources tend to have a far greater impact because they are produced in a smaller geographic range. This results in local concentrations that cause many adverse impacts.
       In Bangkok, Thailand, a city of 10 million, motor vehicles are responsible for 60 percent to 70 percent of the city's air pollution.  Along major transportation corridors the air was found to be dangerous to human health during all of 1989.  The problem is not restricted to foreign cities in poor nations.  In Los Angeles, a megacity of 12 million, a study found that children there have permanent lung damage from air pollution by the age of ten.  In the United States, for example, scientists estimate that urban air pollution may result in the premature death of approximately 50,000 people per year.  Air pollution affects health directly, but it also makes people more susceptible to infectious disease.
       Two air pollutants of special concern are the acid-forming gases nitrogen dioxide and sulfur dioxide.  These pollutants, known as acid precursors, are produced by the combustion of fossil fuels in power plants, factories, and motor vehicles.  Harmful in their own right, they also combine with water in the atmosphere to produce two of the strongest acids known to science, nitric acid and sulfuric acids.
       Acids and acid precursors can be transported hundreds of kilometers from their site of origin dissolved in cloud water. But the acids eventually fall to the ground in rain and snow.  This phenomenon, known as acid deposition, causes incredible damage to the natural and human-built environment.  Acids, for example, eat away at statues and buildings, causing billions of dollars in damage each year.  The Statue of Liberty's recent multimillion dollar face lift was necessitated in large part because of acid deposition.  Destruction of the Parthenon in Greece is attributed in part to acid precursors and acid deposition. Even house paint and automobile finishes may be damaged by acids in the rain and snow.
       Acids falling to the Earth also alter the chemistry of streams and lakes in dramatic ways.  They may increase the acidity directly, killing fish and other organisms.  Acids falling on the watershed of a lake or stream leach heavy metals, like aluminum, from soils.  These toxic substances are then transported to surface waters. Aluminum irritates the gills of fish, causing mucus production.  The amount of mucus produced, however, is so great that fish actually suffocate.
       Acid deposition can be found downwind of virtually any major industrial or population center.  The most severe damage in North America is taking place in the Northeastern United States and Southeastern Canada where hundreds of lakes have been rendered virtually lifeless.  Scandinavia, which lies downwind from highly industrial Europe, has also been hard hit.  In Sweden, for example, 20,000 lakes are without or soon to be without fish as a result of acid deposition.
       In nature all things are connected. Thus, the destruction of aquatic ecosystems can have a marked effect on species that depend on them for food.  Scientists have found that songbirds in Scandinavia, for instance, lay eggs with softer shells than birds feeding near unaffected lakes.  Studies of their bones have revealed elevated levels of aluminum which alters calcium deposition in egg shells and very likely comes from aquatic insects upon which the birds feed.
       Acids kill trees in forests and damage crops the world over, again creating a price tag in the billions of dollars.  Germany's famous Black Forest is a remnant of its former self in large part due to acid deposition.  Many forests in the Northeastern United States are similarly damaged by pollutants carried in by the wind from the Upper Ohio River Valley hundreds of kilometers from the site of destruction.
       Acid deposition has grown steadily as the world's production of nitrogen and sulfur dioxides has grown — a phenomenon that can be linked to growing population, increasing energy demand, and expanding economic activity. 

Altering Our Climate
       Pollutants generated by factories, automobiles, and power plants have also been shown to have an effect on the Earth's climate, locally, regionally, and globally.  Researchers have found that particulates produced by factories, for instance, can substantially increase rainfall in areas downwind from industrial centers. Particulates serve as nuclei upon which water droplets gather.
       Of far greater impact, however, are the effects of pollution on the global climate.  One of the key players in this unfolding drama is carbon dioxide.
       Carbon dioxide is a natural byproduct of cellular energy production, as noted earlier.  It is also released in copious amounts during the combustion of fossil fuels such as coal and oil and by the combustion of organic matter such as wood.  For thousands of years, the level of carbon dioxide in the Earth's atmosphere has been relatively constant.  What was produced by various sources, even natural fires, was absorbed by plants during photosynthesis.  However, as the human population grew and our dependence on fossil fuels increased, carbon dioxide levels began to increase.  In fact, since 1880, carbon dioxide levels in the atmosphere have increased 25%.
       Carbon dioxide is known as a greenhouse gas because it traps heat escaping from the Earth's surface.  This heat is generated by sunlight striking the Earth.  Absorbed sunlight is turned into heat.  Carbon dioxide therefore helps to keep the atmosphere warm and permits life to flourish on this the third planet from the sun.  In fact, without carbon dioxide, scientists estimate that the temperature of the planet would be about 30o C (55o F) degrees cooler than it is today — and clearly inhospitable.
       But like many things in our lives, a little is good, but too much can be dangerous.  Studies show that excess levels of  carbon dioxide and other greenhouse gases (like chlorofluorocarbons and methane) increase heat retention in the atmosphere.  Today, the majority of the world's atmospheric scientists believe that the accumulation of carbon dioxide and several other greenhouse gases is responsible for the measurable increase in the planet's temperature.
       Although the Earth's temperature has risen only slightly in the past few decades and will rise only a few degrees in the next century, according to the most recent projections, slight increases can have profound effects on the Earth's climate and on ecosystems, wildlife, people, and the economy.  One of the projected impacts of the rise in global temperature, known as global warming, is the melting of the polar ice caps and glaciers.  As the land-based ice masses melt, sea level could rise.  A rise in sea level, even of modest proportions, could flood low-lying areas, including many major coastal cities like Miami and New Orleans.  Low-lying nations such as Bangladesh could watch huge portions of their land mass be swallowed by the sea.  Rising sea levels also render coastal  regions more prone to storm surges — water that moves inland during the high seas associated with coastal storms.
       Atmospheric scientists predict that global warming could cause drought to occur with much greater frequency, costing billions of dollars in lost crop production each year, not to mention loss of lives from the effects of heat.  As the world's population increases, global warming could reduce available food supplies, resulting in additional hunger and starvation.  Just how dramatic the decline in food production could be was illustrated in 1988 when record-breaking heat and drought conditions struck the United States.  The protracted spring and summer drought resulted in a 33% decline in grain production and devastating conflagrations like the infamous Yellowstone fire.  Since heat spawns storms in the ocean, climatologists predict that a changing climate will result in more frequent and more violent storms worldwide.
 Deforestation, which decreases the planet's ability to absorb carbon dioxide, is also contributing to the accumulation of carbon dioxide in the atmosphere.  Climate change resulting from pollution and the systematic destruction of the world's forests to meet the needs of the expanding human population could have a devastating effect on thousands of species of plants and animals.  Although some species may be able to adapt to changes in their environment or migrate to more suitable climate zone, the predicted change in global temperature would occur much faster than most species can cope with.  Those species that do persist may be the least desirable.  Some evidence suggests that tropical infectious diseases may spread northward as the climate shifts.

Depleting Natural Resources
      Adding to the troubling list of challenges facing the world community as we enter into the 21st century is the problem of resource depletion — the exhaustion of both renewable and nonrenewable resources.  Renewable resources like topsoil, ocean fisheries and forests and nonrenewable resources such as oil are vital to welfare of the world's people.

Vanishing Farmland: Soil Erosion and Cropland Conversion
       Each day, tens of millions of tons of topsoil are washed or blown from the world's croplands.  Rain water carries this soil into streams and rivers and deposits it in lakes and ponds.  At the current rate of soil erosion, 24 billion tons per year, the world's croplands will lose the equivalent of half of the topsoil on all U.S. farms in the next decade — a huge loss indeed.  This trend is all the more crucial because the very force that is contributing to soil loss and farmland destruction — population growth — necessitates ever increasing amounts of food.  That is, we need farmland to grow food to support the ten million new people added in the U.S. each year.  We cannot afford to be letting it wash away.
       Soil erosion can be prevented or greatly reduced by proper farming techniques such as terracing and crop rotation.  As a result, some people argue that erosion is not the direct result of population growth, but rather a consequence of poor land management.  This is certainly a valid viewpoint and points out the complex connections between population and the condition of the planet.  But population growth often dictates less than thoughtful strategies of resource acquisition — for example, overgrazing.  The pressure to feed people often causes us to overlook the long-term health of agricultural lands and the need to protect them for future generations.

The Steady Loss of Farmland and Ground Water 
       Shopping centers, housing developments, new airports, and highways all have one thing in common.  They are often built on valuable pasture, rangeland, or crop land.  In the United States, an estimated 1400 hectares (3500 acres) of rural land are lost each and every day.  That's the equivalent of 530,000 hectares or 1.3 million acres per year.  But this phenomenon is global in scope.  Although accurate estimates of the worldwide losses are not available, the amount is likely staggering.
       Farmland conversion destroys open space, as housing developments replace grasslands, making cities and towns less attractive.  But it also robs us of valuable food-producing land in an era of unprecedented growth.
       Making matters worse, in many places the groundwater that is pumped to the surface to irrigate cropland is fast on the decline.  Although groundwater is normally recharged by rain and snowmelt, in some key agricultural regions like the Midwestern United States, groundwater comes from deep aquifers that took thousands of  years to fill.  In some heavy-use areas, the Ogallala aquifer, which underlies large portions of Nebraska, Kansas, Colorado, Oklahoma, Texas, and New Mexico, is falling at an astounding rate — one meter per year. The natural recharge rate is about 0.1 millimeter a year — 10,000 times slower than its use.  This problem is all the more important because irrigated land produces a very large share of the world's food supply. 

Declining Fisheries 
       Humans receive an enormous amount of food from the sea in the form of fish and shell fish (clams, oysters, and the like).  But years of habitat destruction, pollution, and over fishing are severely eroding the ocean's ability to provide for human needs.
       Dams and devastating changes in watersheds along rivers of the Pacific Northwest, for instance, have virtually eliminated the salmon.  In 1895, 20,000 tons of salmon were caught annually.  Today, the amount has dwindled to a mere fraction of the original total — about 550 tons per year. This not only makes it harder to feed the world's people, it has had a devastating impact on local economies and individuals who once made a living fishing.  Figure 00 shows the link between the decline in fish catch, population growth, and activity in the watersheds.
       Oceanic fisheries have also been hard hit.  Since 1950, at least two dozen fisheries in the North Atlantic have been wiped out by over harvesting.  Today, 13 of the world's 15 major marine fishing regions are experiencing decreased annual catches.  In four of them, it has fallen by 30 percent or more.  As the world population grows and our demand for food increases, we can expect further decreases.  With it will come additional job losses among the 15 to 21 million people who make a living catching fish and the 200 million people in related industries. 

Vanishing Habitat, Vanishing Species
       Growth in population, resource extraction, and pollution all account for the steady deterioration of the biosphere.  One of the dominant impacts of growth that concerns many citizens the world over is the effect on habitat — that is, the homes of the millions of organisms that share this planet with us.  Birds are a good indicator of the impact of population growth.  Today, 7 of every 10 bird species are on the decline.  Approximately one of every ten species is currently threatened with extinction. Consider the impact of this: The Earth is home to approximately 9600 bird species.  Therefore, nearly 7000 species are declining in number and approximately 1000 species are threatened with extinction.  No one knows the fate of those species on the decline.  Some may survive in decreased number.  Others may vanish altogether.
       Birds are key ecological players.  Predatory birds such as hawks and owls, for instance, help control rodent and rabbit populations.  This helps protect natural systems and provide enormous benefits to farmers and ranchers.  Other bird species like the flicker, flycatcher, and nighthawk, help to control insect populations, another function vital to ecological health and the well being of farms.  Nectar-feeding birds such as the delicate and fascinating hummingbirds of North America are also pollinators.  As they acquire food from plants, they spread pollen and fertilize a variety of useful and beautiful plants.  Fruit- eating birds help disperse seeds of the plants they dine on.
       Howard Youth of the Worldwatch Institute notes that "Most bird species are declining because natural balances are being knocked askew by the global expansion of humanity."  He notes that their habitat is being destroyed or they are being over hunted or poisoned by pesticides or even out-competed by species introduced by humans.  All of these factors increase as human population expands.
       The white stork of Europe exemplifies the biological impact of population growth.  This species was once a common site in many towns in Europe.  But since the 1960s, the stork population has fallen by two-thirds.  In many areas they have vanished completely.  The most immediate cause for this marked decline is the draining of wetlands — crucial feeding sites — to make room for farms and housing developments all to accommodate the growing human population.  In their winter habitat in sub-Saharan Africa, the birds succumb to pesticides sprayed on crops to protect them from insects and boost productivity — once again to feed a rapidly growing population.
       Virtually every habitat on Earth is under pressure from the expanding human population.  Tropical rain forests, home to at least 3500 of the world's bird species, are fast on the decline.  Current estimates suggest that 340 square miles of tropical rain forest are lost each day.  To date, nearly 3 million square miles of tropical rain forest — an area approximately half the size of the United States — has been lost.
       Rain forests are cleared to harvest valuable hardwoods for the parquet floors seen in U.S. shopping malls and homes.  The teak wood of yachts also comes from rain forests.  These magnificently rich forests are also cleared to make room for cattle ranches and mines.  Many acres have been cut to plant cash crops such as bananas, tea, and coffee.
       Another well known victim of expanding population are the temperate rain forests of the U.S. Pacific Northwest, which have been cut with wanton abandon in recent decades to provide wood and a host of wood products.  Only about 3 percent of the original old growth forests remain.  Grasslands the world over have been plowed under to make room for crops.  Deciduous forests of the eastern United States have also been heavily cut.  Only a fraction of the original forested land remains.
       Watery habitats are also feeling the pressure of human population expansion.  Wetlands, a broad category of ecosystems that includes swamps, bogs, coastal marshes, and other similar lands that are wet perpetually or some part of the year.  Wetlands are fast disappearing throughout the world.  In the United States, wetlands once covered an area the size of Texas.  Today, less than one-third of America's wetlands are left.  In fact, in the past 200 years, wetlands have vanished at a rate of 24 hectares (60 acres) per hour! Despite increased awareness of the problem, wetlands are still vanishing at a rapid pace.
       Species extinction is one symptom of human population growth.  More alarming than the actual number of species that are now endangered or extinct, however, is the rate at which species are vanishing from the biological slate.  Currently species are vanishing at a rate 100 to 1000 times greater than natural extinction rates.  If, however, all of the species that are currently threatened vanish, the rate in the next century could skyrocket to 1000 to 10,000 times the natural rates prior to human evolution.
       The loss of natural habitat and wild species is not just an ecological or aesthetic deduction from our planet's once-vast assets.  It is an economic loss as well.  Each acre of coastal marshes provides the equivalent of $85,000 in water purification.  The water storage capacity and hence flood protection and aquifer recharge services provided by a 223,000-hectare swamp in Florida, for instance, was valued at $25 million per year!  Replacing the flood control and storm protection of a single kilometer of mangrove swamp in Malaysia was valued at $300,000 — the cost of building rock walls to replace the swamp.

Crowding, Urban Pollution, and Infectious Disease
       During the late 19th and much of the 20th Centuries, the medical community grew increasingly optimistic about the prospect of conquering infectious diseases.  Caused by viruses, bacteria, and a host of other organisms, infectious diseases currently claim the lives of 17 million people a year worldwide.
       Infectious diseases are spread in a variety of ways.  Some are transported in water or through the air. Others are transmitted by insects like mosquitos, while others contaminate foods or trade goods.  Still others are spread through person-to-person contact.
       The discovery of antibiotics and vaccines and improvements in sanitation in the past century, though, helped to curb the spread of disease and spawned much hope among citizens and health officials that science would completely eradicate infectious diseases.  By the late 20th Century, however, optimism changed to concern.  Scientists found that as the world population grew and as the density of population increased, infectious disease began to rise once again, threatening the possibility of potentially devastating global epidemics that could dramatically increase the death rate of many countries.  But crowding was not the only factor stimulating the growing concern for infectious disease.  Increased international travel by plane, which greatly enhances the spread of disease, has many scientists worried, as does human encroachment on once-wild areas that increases the risk of exposure to new and deadly disease organisms like the infamous ebola virus.
       The rise in infectious disease has spawned a modern health-care crisis.  It will result in untold pain, suffering, and death.  And it carries with it a huge price tag.  The cost of medical treatment and losses in worker productivity due to infectious disease is staggering and can put a serious strain on a nation's economic resources, especially in less-developed countries that can scarcely afford basic medical care.

Crowding and Disease: The Deadly Connections
       In 1995, about 2.7 billion people, nearly half of the world's population, lived in  urban areas.  All trends indicate that this number is bound to increase.  Demographers, scientists who study populations, predict that the number of cities containing more than one million people will increase from 280 in 1990 to 500 to 700 by 2015.  Cities with more than 10 million people will increase from 21 today to 30 or more by the year 2015. The world's urban population is growing three times faster than rural populations, meaning only one thing: more and more of humanity will be restricted to close quarters.
       People living close together create breeding grounds for epidemics, outbreaks of infectious disease.  Crowding enhances the spread of infectious disease from one person to another.  In addition, urban populations produce enormous amounts of municipal solid waste, which is often dumped carelessly or, even if hauled away from dwellings, is improperly disposed of in open dumps.  The mishandling of solid waste creates conditions rife for intermediate disease hosts such as insects or rats that may then infect humans.
       In 1996, Dutch researchers studying infectious disease and crowding found that overcrowding increases not only the transmission of disease but also the risk of multiple infections.  As noted earlier, people who are malnourished are especially prone to infectious disease and much more likely to die than their well-fed counterparts.
       In many developing nations, rural residents migrate to cities en mass in search of a better living.  But they often find the promise of prosperity in the city is illusive.  What they encounter is high unemployment, filth, crime, stress, and food shortages.  Many immigrants to urban settings settle in squatter camps on the perimeter of the wealthier areas.   In these locations, they often have no access to clean water, sanitation facilities or waste removal.  As such, they become breeding grounds for infectious disease.   In 1983, researchers studying Buenos Aires, Argentina found the incidence of tuberculosis, an infectious disease caused by a bacterium that invades the lungs, was three times higher in the surrounding slums than in the central metropolitan area.  Untreated, tuberculosis kills its victims in one to two years.  Scientists have reported that infectious disease occurs at higher rates in the poorest sections of many major cities, including Sao Paulo, Brazil and Seoul, South Korea, the second and ninth largest cities in the world, respectively.
       Population growth enhances the spread of infectious disease but has other effects on people as well.  One of them is pollution, described earlier.  Air pollution has many direct effects, but studies have also shown that air polluted with industrial emissions and auto exhaust weakens peoples' immune response and therefore increases their susceptibility to airborne infectious agents.
       More people also means more sewage.  In many crowded cities, streams and rivers are severely polluted with human wastes carrying pathogens.  Municipal water systems, which provide water to residents, can also transmit disease-causing organisms, known as pathogens, to huge numbers of people.  According to a 1993 report by the U.S.-based nonprofit organization, the Natural Resources Defense Council, the bacteria, viruses, and protozoa that occur in U.S. drinking water cause 900,000 Americans to become ill and kill about 900 people annually.  Those that succumb are usually the very young, the elderly, and people who are weakened by diseases such as AIDS, cancer, pneumonia, or surgery.
       The role of municipal water systems in the spread of diseases was amply illustrated by a 1993 outbreak of a protozoan parasite, Cryptosporidium, in Milwaukee, Wisconsin.  During this incident, more than 312,000 residents became ill with severe flu-like symptoms.  Eight people died.  Workers at Mil waukee's water purification plant found large numbers of the parasite in water that had already been treated — water that was being pumped to people's homes.  Cryptosporidium comes from the intestines of land-dwelling animals and was washed into the water source by heavy spring rains.  Normally, a sophisticated filtration process would have removed all of the organisms, but the plant's filter system was not operating at peak efficiency for a few days, which permitted them to invade the water system.
       In Mexico City, treated sewage effluent is used to irrigate crops, contributing to the spread of parasitic diseases.  Fortunately, drinking water can be filtered or boiled to make it safe.  But diseases that spread through the air have no such controls, making crowding an extremely dangerous proposition.  Each year, 8.8 million people contract tuberculosis, caused by an airborne bacterium.  About 2.7 million of these people die. 

The Dangers of Air Travel and Trade 
       When most of us think about the dangers of air travel, we ponder the horrifying possibilities of crashes.  But the danger of air travel is far greater that these rare but catastrophic possibilities.  As many who travel through crowded airports during the holiday seasons can attest, airports are a major source of infectious disease.  Air travel has become a major route for the global spread of pathogens.
       Infected individuals traveling to foreign lands carry with them a host of bacteria and viruses.  In fact, within two years of the emergence of a new influenza virus, 50 percent of the world's population has been exposed to it, thanks in large part to commercial air travel and crowding in urban centers.  International air traffic has risen from 163 million passengers in 1980 to over 321 million in 1993, the latest year for which data were available.
       The US Center for Disease Control in Atlanta, Georgia warns that infected travelers transport viruses worldwide.  Every city in the United States is accessible from anywhere in the world within 36 hours — well within the incubation period of all infectious diseases.  This means that an infected person can travel abroad carrying a disease before he or she is even aware of it.
       International trade carries bountiful products worldwide, but pathogens may occasionally be along for ride, attached to those products or their containers.   Shipments of used tires brought the Asian tiger mosquito into the United States, South Africa, New Zealand and southern Europe.  This mosquito and another closely related species carry dengue fever and yellow fever.  Although the Tiger mosquito is a tropical species, scientists have found that it is able to survive cold winters and has recently spread into Latin America and northward into the United States.  Each year up to 100 million people, mostly urbanites, are infected worldwide with dengue fever.  Dengue fever is viral in origin.  It results in intense headaches, diarrhea, and internal hemorrhaging.  Yellow fever varies from mild to severe symptoms, which include fever, chills, backaches, nausea, vomiting and worse: internal bleeding, liver failure, and kidney failure are common.
       Cholera, a waterborne disease caused by a bacterial pathogen, has been known since the 19th century and largely confined to Asia.  This disease results in diarrhea, vomiting, rapid dehydration, and kidney failure. If untreated, it is usually fatal.  Treatment only increases survival rates to 50%.
 In the 60s and 70s the disease began to appear in Europe, Africa, and the South Pacific.  There were no known indigenous cases of the disease in the Western Hemisphere for 60 years, but in the 1970s, cholera surfaced in Texas and Louisiana.  Then, in 1991, the disease appeared in a Peruvian port city, introduced by the dumping of ballast water from a Chinese freighter.  Cholera spread quickly and relentlessly across the hemisphere.  In 1992, 460,000 cases were reported and by 1994 over 960,000 cases had been reported in 21 countries in the Western Hemisphere. 

Venturing Into Dangerous Territory 
       As the world population grows, it spreads out on the planet, invading habitat of other species, including habitat of new pathogens.  People have encountered new viruses with deadly consequences.  One family of viruses causes hemorrhagic fever or intense often fatal bleeding with fatality rates as high as 90 percent.  Two members of this family or diseases are the ebola and lassa virus.  Outbreaks of these and related viruses have occurred in South America, Africa, Russia, and the United States, causing panic.  As individuals infected with these viruses leave rural homelands in search of the work in cities, they may carry with them diseases that can spread quickly in the urban environment.
       Habitat disturbance can also have a profound effect on disease organisms.  As people flee U.S. cities for more rural settings, housing developments built to accommodate them ward off predators such as the wolf, mountain lion, and coyote.  Because of this, suburban New England populations of deer, raccoons and mice have soared.  Grassy lawns, garbage cans, and dumps provide a ready food source for these species, but the proximity of people to these animals has resulted in an epidemic of Lyme disease, caused by a bacterium carried on ticks. Lyme disease results in fever, fatigue, headaches and swollen lymph nodes.  If untreated, it can lead to severe joint pain, arthritis, and neurological disorders.  Lyme disease is recognized as a danger now in 47 states with over 13,000 cases reported in 1994.
       Stephanie Schrag of the Department of Biology at Emory University, Atlanta, Georgia and Pamela Wiener of the Department of Biological Sciences at University of Warwick, Coventry, United Kingdom wrote in the August, 1995 issue of Trends in Ecology and Evolution, "Changes in pathogen and host ecology may be primarily responsible for the emergence of the majority of currently spreading diseases." The authors note that seemingly minor changes can result in new outbreaks.  As the human population expands and the environment is altered to accommodate this growth, expect the incidence of new infectious diseases to increase.
       Consider an example.  In certain areas of Argentina, farmers changed their production techniques and crops to increase yield and profit.  With these changes, came an explosion in the population of a small field mouse, which carries the deadly Junin virus. This virus eventually infected more than 20,000 Argentineans, killing one third of them.   A proliferation of this same species of mouse later caused outbreaks of the deadly virus in Bolivia, Venezuela, and Brazil.  Another mouse is the likely carrier of Lassa virus, an African virus similar to Ebola.  Outbreaks in at least five countries including the United States have lead to widespread panic.
       Many, if not all of these pathogens and diseases have been around for years.  But as humans push further into new environments to meet the needs of an ever-growing population for food, shelter, building materials, and so on, ecosystems are altered.  In an undisturbed ecosystem, an intricate set of checks and balances  keeps microbes and their hosts in check.  However, because of the speed with which microbes grow and reproduce, many disturbances in their environment favor the microbes.  The more disturbance, the greater the exposure risks.
       However, moving the microbes to the people's territory or moving  the people into the microbes',  is not always sufficient cause for a serious outbreak of disease.  Living conditions, weather, and environmental disturbance all play a role in the spread of these organisms that were once held in check.  In Surat, India, for example, an outbreak of bubonic plague resulted from a combination of natural disaster and overcrowding.  Monsoon flooding in 1994 that followed a devastating earthquake the year before forced many homeless people into closer quarters with disease carrying rodents.  The medical system was not prepared to treat the epidemic of plague, which had not been seen in the area for over 40 years.
       Rapid, large-scale modification of the environment by fires, storms, earthquakes and other natural phenomena is not new to nature.  However, only recently have humans created ecological change of comparable magnitude.  Humans destroy over 78.8 million acres of rain forest each year — an area equal to Massachusetts, New York, Maryland, and Wisconsin combined.  This destruction of the species-rich rain forest ecosystem threatens extinctions of uncountable wild plants and animals.  Bacteria, viruses and parasites once maintained harmlessly in those hosts are increasingly "forced" to find new hosts. 
       As the population grows and resource demand increases, efforts are made to increase productivity of existing lands.  Dams, irrigation canals, and other water projects create new farmlands and fisheries, but also create new breeding grounds for water-borne diseases like schistosomiasis, malaria, cholera, and typhoid.   A canal built in India to irrigate desert provided the water needed to breed malaria-carrying mosquitos.  Instead of bountiful crops, deadly strains of the disease infected the farmers and field workers who came in search of food and prosperity.
       Another factor of grave concern is the emergence of genetically resistant strains of pathogens and insects, which transmit them.  Antibiotic treatment of a bacterial infection, for example, may kill 99.9% of the "bugs", but the remaining 0.01% survive because of naturally occurring resistance to the medicines.  This small genetically resistant population may proliferate and when the bacterium strikes again, doctors find they must increase the dose of the antibiotic or switch to a new one.
       Bacteria, viruses, and parasites thus adapt to drugs.  In a similar manner, insects that transmit some infectious organisms also adapt to insecticides.  Of the five most deadly infectious diseases worldwide (pneumonia, diarrheal diseases, tuberculosis, malaria and measles), all except measles (which is a virus) now appear to have drug-resistant strains.  In some cases, new strains develop resistance to several drugs simultaneously.  Multi-drug resistant tuberculosis costs twenty times more to treat and the results are poor, with mortality rates above 50%.  The worldwide threat of malaria has increased as the parasite that causes the disease has become drug resistant.  But there's another danger lurking.  The mosquito that carries the malaria parasite has also become resistant to once-powerful insecticides used to control them.  The combination of the two could be quite challenging, to say the least.

Population and the Future
       Scientists are working on strategies for coping with the overpopulated world of the future.  To do this, they must first estimate how large the population will become.  Unless there is dramatic change, they must then find ways of providing for the needs of so many people.  But determining the future growth of the worlds' population is a difficult task for demographers.  Demographers base growth rates and projections on three factors: fertility, mortality, and migration.  Migration is an important factor for individual countries but not for the world as a whole.  All three variables can change rapidly, which in turn can alter predictions.  Like weather forecasts, today's population predictions may turn out to be tomorrow's mistakes.
       Scientists have been able to draw conclusions.  First, continued world population growth is inevitable.  Second, the size of the human population is likely to increase quickly and substantially.

The Numbers
       In 1997, demographers at the United Nations predicted that the world population would climb to 9.4 billion by 2050, up "only" about 3.5 billion from 1997.  Estimates by other organizations range from about 8 billion to 11 billion.  The latter figure is almost twice the world's population in 1997.
 Demographers use past population trends to help them make their predictions.  For example, the U. S. Bureau of Census reported that the world's population grew by about 80 million people in 1996.  That figure, which was confirmed by the UN Population Division, was 6 million fewer than the 86 million by which the global population grew in 1994.  It was also significantly less than the estimated 90 to 100 million that were added each year to the world's population in the 1980s.
       The U. S. Census Bureau reported that shrinking family size had much to do with the population decrease.  The Bureau said that the word's total fertility rate — the number of children born per woman during her lifetime — declined to 2.9, the lowest level ever recorded.
 In 1985, the worldwide total fertility rate was 4.2.  A study released by the UN in 1997 also found that fertility rates were dropping faster than experts had predicted.  Another factor contributing to the decline in population growth was an increase in death rates and declining life-expectancy in Africa, Eastern Europe, and the former Soviet Union.  Scientists attributed the increase in death rates to AIDS, other infections, disease, and war.
       Some scientists were encouraged by the statistics indicating a slowing in the rate of population growth.  The Washington, D.C.-based Population Institute, in fact, speculated that this decline could result in a stabilization of world population at 8 billion by the year 2025.  That projection, however, still represented a major increase in population over the 5.8 billion people in the world in 1997.  Furthermore, some scientists warned that conditions could change, rendering current projections obsolete.
       For example, they said, reversals in the decline of life expectancy in the regions where that has been occurring, together with increases in fertility in some countries, could increase the rate of world population growth.  Or fertility could continue to fall and death rates to rise, resulting in a further decline in growth.  In either case, however, the world's population would continue to increase — whether at a fast or slow pace.
       A growing population in the United States will add to that increase, though by how much was still a matter of debate.  In 1997, the population of the United States was about 265 million.   In 1988, the U.S. Bureau of Census had estimated that by 2050 the population of the Untied States would stabilize at 290 million to 300 million.  In 1993, however, the Census Bureau revised its projection upward, based on rising fertility, continuing high levels of immigration, and increasing life spans.
       The Bureau predicted that by the year 2050 the U.S. Population would reach 392 million.  The Bureau saw no signs of the population stabilizing in the near future.  An addition of almost 130 million people in the United States in a little over 50 years could place a significant strain on already limited resources, including land, food, and water.
       Because all population experts agree that the world's population will continue to increase, they are calling for plans to deal with the situation.  According to the experts, strategies for addressing population growth fall into two main categories: 1) measures to produce more food and to reduce pollution, waste, and resource depletion brought on by more people; 2) and measures to slow population growth itself.

Can we produce more food?
       Efforts are underway today to boost the per-acre yield of crops, mainly through more intensive use of irrigation and fertilizers.  Scientists are also investigating the use of genetic engineering to increase crop yield.  They have already been successful in genetically altering some crop plants, enabling them to resist disease and insects.  But some agricultural experts questioned whether future food production increases can match those achieved since the 1960s, when higher-yielding varieties of food plants, especially rice, were introduced.
       Another strategy for increasing food production involves the conversion of nonagricultural land to farm production.  This usually means cutting down forest and plowing grasslands to make room for crops.  In many parts of the world including Asia, however, all arable land is already being cultivated.  In regions with substantial reserves of unused land — notably Africa and South America — much of the land is of marginal value or is vital wildlife habitat.  The soils of tropical rain forests, for example, are very thin and infertile.   Moreover, cutting down tropical forests to make room for farms hastens the loss of species.

Protecting the Environment
       Lessening the impact of human beings on the environment is a major concern as the world's population grows.  Some nations are pursuing a variety of strategies to accomplish this goal.  One approach has been to improve the efficiency with which resources such as fossil fuels are used.  Some nations have also promoted the use of renewable energy sources.
       Renewable sources of energy are significant alternatives to fossil fuels, which are responsible for many major environmental problems, such as global warming and acid precipitation.  Renewable energy sources include wind power, solar energy, hydroelectric power, and geothermal energy.  The use of most of these energy sources has very little impact on the environment.
       Scientists have already created ways to capture and use the energy of the sun.  For example, they have developed photovoltaic cells, thin silicon wafers that convert sunlight into electricity. 
       Recycling industrial and municipal wastes offers another enormous opportunity to lower human impact on the planet.  Recycling not only reduces the amount of garbage dumped into landfills, it also lowers the demand for raw materials.  Every aluminum can that is recycled, for instance, reduces the need to mine more aluminum ore.  Every ton of newspaper that is recycled saves 17 trees.  What's more, producing goods from recycled materials can be cheaper than making them from raw materials, in part because it requires less energy.  This in turn substantially reduces the amount of pollution emitted by factories, another plus for the environment.

Family Planning
       All these actions, experts say, are essential for creating a sustainable future and for maintaining a healthy economy while protecting natural systems.  But the most important action is to stabilize human population growth, which means reducing birth rates still further.
       Because of the wide range of birth control options, most countries fashion strategies to reduce family size in ways that are socially and morally acceptable to their citizens.  Most population control programs focus on family planning, education, and economic development.
       The majority of the world's nations had some form of family planning program in force in the 1990s.  Family planning enables couples to determine the spacing and number of their offspring.  National programs in the less-developed nations often educate couples about the desirability of smaller families.  China promotes the one-child family.  Most nations throughout the world also provide free or low-cost birth control measures, such as condoms, birth control pills, diaphragms, and sterilizations.  Many states in India have developed programs that encourage men to undergo voluntary sterilization in the hope of reducing the birth rate.
      Most people in industrialized nations have agreed that some form of family limitation, or at least more widely spaced births, is desirable for the good of both the family and society.  But individuals and groups, especially some religious groups, differ sharply on the methods of birth control that they consider morally acceptable.  The governments of many countries are striving to reach compromises with their citizenry on these issues.

The role of women and education
       For several decades, population stabilization strategies focused almost entirely on family planning.  In the 1990s, however, many people came to realize that the population dilemma could not be solved simply by family planning programs alone.  They saw that other factors in a nation, such as the educational level and economic prosperity of its citizens, also had profound influences on family size.
       For example, women who decide to pursue an education often chose to delay childbearing.  Obtaining an education also provides women with an opportunity to pursue careers.  As a result, they tend to have fewer children.
       Efforts to improve education and enhance the economic opportunities of women can also bolster a woman's status in society, especially in developing nations.  In many developing nations, a woman's value is based on the number of children, often male children, she bears.  But, experts contend, educational and economic opportunities could create shifts in cultural beliefs and eventually change ways of thinking about women.  If women's self-esteem and perceived worth are no longer tied solely to childbearing, family size may decline.
       Education and enhanced economic opportunities are also important for men in the developing countries.  Male responsibility in family planning decisions could be enhanced by education.  Further more, better education of men could serve as a springboard for broader social change aimed at rethinking the status of women in society.  A better-educated society is also more likely to become economically successful and a couple who are prosperous in their careers may decide to delay having children.
       The threat of global overpopulation is probably the most important issue of our time.  Scientists will continue to study this and the associated problems, such as pollution and loss of species, that are directly linked.  Their hope is that citizens and government leaders everywhere will acknowledge the seriousness of the situation and work with them to find creative solutions to the population explosion; solutions that can lead to a healthier — and roomier — society.                                                                                      BACK TO TOP