The Human Population

Human Population History:

• 2,000 years ago the estimated human population was 150 million
• By 1850, the human population was one billion. By 1930, it was 2 billion.
• It took 10,000 generations to reach 2 billion.
• The human population is now growing at a rate of about 3 people/second or 260 thousand/day or 1.8 million per week or 93 million/year

• Every 3 years, the global environment must support another 285 million people.
• Even the U.S. population is growing fast. We're currently adding the equivalent of three Washington, D.C.s every year; another New Jersey every 4 years.

U.S. at night

• How many of us are there? Click on the rotating Earth!

As a result of this rapid growth:

• Approximately 1.3 billion of the world's people are impoverished, living on the equivalent of less than 1 dollar a day. And as population steadily increases, the gap between rich and poor is widening.
• Some 60% of the 4.8 billion people in developing countries lack basic sanitation, and almost one-third have no access to clean water.
• Nearly 1 billion people in the world are illiterate, two-thirds of them women.
• Despite increases in grain production that began in the 1950s, thanks to "miracle wheat" and other advances in    agricultural technology, such increases seem to have leveled off in recent years. Some 841 million people today are chronically malnourished, and there are 88 "food deficit" countries. This means "they can neither feed themselves nor afford the imports they need," according to the United Nations Population Fund, a subsidiary of the UN General   Assembly and the largest internationally-funded source of population assistance to developing countries.

When a country darkens on this map, it represents a death caused by hunger.

• Supplies of water for irrigation are declining around the world as underground water reserves - aquifers - become depleted faster than nature can fill them. Groundwater overdrafting is now widespread in the crop-producing regions of central and northern China, northwest and southern India, parts of Pakistan, much of the Western United States, North Africa, the Middle East, and the Arabian Peninsula.
• Nearly half the earth's land mass already has been changed by human activity - wetlands filled in, forests cut down, prairies plowed under. Runoff from farms, industries, and urban areas has resulted in some 50 "dead zones" in

coastal waters.
• Among the ocean's 200 major fish stocks, 35% are in decline, and another 25% are being fully exploited.
• Species are going extinct at a faster rate than ever before, including the time when dinosaurs were dying out.

Factors Contributing to the Population Explosion:

• The green revolution
Agricultural advances have insured that no one has to starve. For thousands of years, the Earth's carrying capacity depended on the available food supply. That is no longer the case.
• Advances in medicine
Disease has throughout history always been the definitive factor in the limiting of the human population. However, medical research has largely controlled (or eliminated) such diseases as smallpox, malaria, & cholera. As a result, death rates have declined dramatically.
•  The industrial revolution
An increase in the availability and use of technology has lead to a more densely packed society that attempts to make room for an ever increasing population. The influx of new technology into the global market over the past 150 years has made life generally easier in the industrialised nations of the world and led to promising social situations that provoke the tendency of people to have more children.
• Other factors:
• In some countries people lack awareness of birth control or the ability to limit the size of their families. Recent United Nations statistics indicate that 90% of women in 10 African nations had not heard of contraception.
• People in some developing countries who do want to limit the growth of their families lack access to contraception or reproductive-health services. Family planning methods are simply not available in large sections of the world. As many as 500 million women in developing countries live too far from health centers to obtain contraceptives, & unsafe abortions kill an estimated 70,000 women a year.
• Human reproduction is a matter of great religious and cultural importance as well. The religious teachings of many people prohibit or discourage contraception. And some cultures traditionally value large families as a sign of prestige and power.

Population growth:

• The overall rate of population increase depends on the number of births and deaths, but also on the length of generations -- the age at which women have their first baby.
• For example, if all women had three kids with a 15-year average generation time, the rate of population growth would be 2.7%. If the average spacing were 30 years, the growth would drop in half -- to 1.35%.
• How does percent population growth translate into 'doubling times?'

Population Age Structure:

Birth and death rates do not tell the whole story of population growth. A country's TFR can be below replacement level while the population continues to grow, if there are a disproportionately large number of couples in these younger age groups. That is the situation in Kenya and, to a lesser degree, the United States. The age structure of the population, then, is also an important factor in population change (see the population pyramids for Kenya, Sweden, & the U.S. above). When a substantial proportion of a country's population is young, high population growth rates in a country are to be expected, even if the average TFR is modest. The reason is that so many females are of  childbearing age, that even a modest average TFR results in a large number of births.
 
 

Fertility Rates:

• Replacement-level fertility = the number of children a couple must bear to replace themselves
• slightly more than 2 children because some children die before reaching their reproductive years
• reproducing at this level does NOT mean that population growth stops; there are so many "future parents" already alive that, even at replacement-level, population will continue to grow for many years
• Total fertility rate (TFR) - estimate of the average number of children a woman will have during childbearing years
• In 1995, the TFR was 3.1 children per woman (1.6 in MDCs & 3.5 in LDCs); still far above replacement level

This map shows the average number of children born to a woman during her lifetime. The darker the color, the greater the
number of children. For example, France at 1.7 children has a lower fertility rate than Egypt at 3.6 children. The total fertility
rate (TFR) is the average number of children a woman would have, assuming that current age-specific birth
rates will remain constant throughout her childbearing years (usually considered to be ages 15-49).

• Fertility rates in the United States:

• Peaked in 1957 at 3.7 children/woman

• At or below replacement level (2.1) since about 1972 because:
• widespread use of birth control
• availability of legal abortion
• social attitudes favoring small families
• increasing cost of raising a child to age 18 ($177,000 for low-income family, $231,000 for middle-income & $335,000 for upper-income)
• increase in average age of marriage between 1958 & 1992 (from 20 to 24.4 for women, and from 23 to 26.5 for men)
• More women working outside home (child-bearing rate of "working" women 1/3 that of women not in paid labor force)
• delayed reproduction

• The U.S. population is still growing faster than most MDCs:

• In 1995, the U.S. population grew by 1.18% (3.1 million people) more than double mean rate of world's industrialized nations.
• The U.S. population is projected to increase from 263 million to 345 million between 1995 & 2030, with no leveling off anticipated
• This projected growth of the U.S. population is due to:

• large number of baby boomer women still in child-bearing years (i.e., lots of potential mothers)
• increase in number of unmarried mothers (including teen-agers)
• higher fertility rates for women in some racial & ethnic groups than for Caucasian women
• high levels of legal/illegal immigration (about 40% of current growth)

• U.S. population growth is very important because of the impact that each of us has on the environment. For example:

Earth's Carrying Capacity (is the Earth overpopulated?):

• Carrying capacity is the number of organisms an environment (e.g., the Earth) can support
• determined by: food production, living space, waste assimilation, & resource availability
• for humans, carrying capacity can be expanded through advances in agriculture, industry, & medicine
• Some believe Earth's carrying capacity has already been exceeded as illustrated by:
• polluted air
• depleted fisheries
• The world's marine catch has increased more than four times in the past 40 years -- from 18.5 million tons in 1950 to 82.5 million tons by 1992. This staggering growth has resulted in overfishing and wasteful, destructive fishing practices worldwide which now threaten the lives of hundreds of millions of people who are vitally dependent on fishing for food and livelihoods. They face resource depletion, competition from industrial and distant water fleets, and loss of access to traditional marine food supplies.

 
• deforestation
• Continued forest loss and degradation will have serious implications at local, regional, and global levels. Exploitation and clearance of natural forests are destroying the environment and way of life for tens of thousands of indigenous people. Disappearing forest cover also represents incalculable losses in biological diversity and ecological services, including nutrient recycling, watershed management, and climate regulation.

• species extinction

• denuded landscapes
• global warming

• starvation
• poverty
• and so on
• Others are more optimistic & believe Earth could support many more people
• More people = more productivity = more knowledge = better production methods + discovery of new substitutes, and so on

Impacts of continued growth in human populations include:

• increased hunger/starvation while food production levels off or even declines (i.e., less food/person)

While grain yields per acre have been increasing steadily until 1990, the rate of  increase has fallen off in the last 10 years. Most of the benefits of irrigation, machinery, fertilizer and plant breeding have already been realized. The production of grain per acre is close to the maximum obtainable through photosynthesis. Geneticists are working on improving the efficiency of photosynthesis, and that may turn out to be possible, but given that nature has been working on the problem for several hundred million years, there is no guarantee that we can improve on the process in the next 10 to 20 years.

• increasing desertification
• Desertification is the conversion of productive rangeland or cropland into desertlike land. It is usually caused by a combination of overgrazing, soil erosion, prolonged drought and climate change.

Arable land per person

• increased number of refugees
• increased urbanization
• Cities may offer opportunities for the people of developing countries. However, the danger lies in the structural inadequacies typical of many cities in these countries. The most obvious of these inadequacies are those of public sanitation. Insufficient or non-existent sewage systems in exist in many parts of these cities. Water supplies can thereby become polluted, leading to the high incidences of disease.

• emerging diseases

• dying seas & rivers, for example:
• Colorado River

• Gulf of Mexico dead zone

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Where are we headed?:

Maximum Global Population Guesses (McCluney 1999):
 

Text of the message of Secretary-General Kofi Annan to mark World Environment Day, 5 June 2000:

We may be at the dawn of a new millennium, but the environmental problems we face are painfully familiar. They may even be
getting worse. Despite the Earth Summit, and despite success stories like the Montreal Protocol to protect the Ozone Layer,
human beings continue to plunder the global environment. Unsustainable practices remain deeply embedded in the fabric of our
daily lives. We are failing to protect resources and ecosystems. We are failing to invest enough in alternative technologies,
especially for energy. We are failing even to keep the debate alive.

These are deeply troubling trends. I recommend four priorities for reversing them.

• First, we need a major public education effort. Understanding of the challenges we face is alarmingly low. Corporations and consumers alike need to recognize that their choices can have significant consequences. Schools and civil society groups have a crucial role to play.
• Second, environmental issues must be fundamentally repositioned in the policy-making arena. The environment must become better integrated into mainstream economic policy, and the surest way is through green accounting.
• Third, Governments must not only create environmental agreements, they must enforce them. They can, for example, cut the subsidies that sustain environmentally harmful activities each and every year. They can also devise more environment-friendly incentives for markets to respond to.
• And fourth, we need sound scientific information. This is the only basis for effective policy, yet large gaps in our knowledge remain.

Useful links:

NumbersUSA

Overpopulation.org

Why six billion?

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