|Biodiversity and Conservation|
source ref: biobook.html
HUMAN POPULATION GROWTH
CARRYING CAPACITY OF THE EARTH
REGIONAL DIFFERENCES IN POPULATION PROBLEMS
"Humanity's impact on the earth has increased extinction rates to levels rivaling the five mass extinctions of past geologic history, transformed nearly half of Earths land and created 50 dead zones in the worlds oceans" - Environment News Service
"Insurance companies are subsidizing population growth by paying for Viagra, yet many refuse to cover the contraception that women need to help them plan their families" - Carl Pope, Executive Director of the Sierra Club |
Latest population figures from the U.S. Census Bureau
Planet Earth 2025: A look into the future
world of 8 billion humans by Don Hinrichsen and John Rowley.
Worries about human population growth are not new. Over 200 years ago (1798) Thomas Malthus published An Essay on the Principle of Population. In this book he pointed out that the human population tends to grow geometrically, while the resources available to support it tend to grow arithmetically. Under these conditions the population must inevitably outgrow the supply of food that is available to fulfill its needs. He postulated that population growth was already outpacing the production of food supplies in 18th-century England. He predicted that population growth would lead to degradation of the land, and eventually massive famine, disease and war. Malthus presented his theory in response to optimists of his day who thought that mankind's ability to master the environment was limitless. Improvements in agriculture and the industrial revolution postponed the disaster that Malthus thought was imminent. But his ideas are even more applicable today.
Especially since 1960, several developments have dramatically reduced infant and child mortality throughout the world: the use of DDT to eliminate mosquito-borne malaria; childhood immunization programs against cholera, diphtheria and other often-fatal diseases; and antibiotics. During the same period, the "Green Revolution" greatly boosted food output through the cultivation of new disease-resistant rice and other food crops, and the use of fertilizers and more effective farming methods. These changes have contributed to a dramatic increase in human population growth rates.
The Earth's population reached 6 billion in September, 1999 (Updated total). It will increase this decade by another billion, the fastest population growth in history. It was only 2 billion in 1930, so today's older generation was the first in history to see a tripling of the Earth's population during their lifetimes! Every second, three people are added to the world; every day a quarter of a million (2 times the population of the city of Irvine) are added. Every year, about 87 million people (about the population of Mexico, or 3x the population of California, or the combined populations of the Philippines and South Korea) are added to the world. During the next 2.5 years, the equivalent of the U.S. population will be added to the planet. During the coming decade the increased population of one billion people is the equivalent of adding an extra China to the world's population. A recent joint statement by the U.S. National Academy of Sciences and the British Royal Society finds that population is growing at a rate that will lead to doubling by 2050.
The Worldwatch Report: Shifting views of population
Obviously the earth cannot continue indefinitely to sustain population growth at the current rate. How many people can it support?
Ecologists have often made use of the concept of carrying capacity in addressing the pressures that populations put on their environments. Carrying capacity is simply the largest number of any given species that a habitat can support indefinitely.
One way of analyzing carrying capacity of the earth is to calculate its net primary productivity (NPP). This is the total amount of solar energy converted into biochemical energy through plant photosynthesis, minus the energy needed by those plants for their own life processes. It represents the total food resource on earth.
It has been calculated that, prior to human impact, NPP was about 150 billion tons of organic matter per year. By deforestation and other forms of destruction of vegetation, humans have destroyed about 12% of the terrestrial NPP, and now directly use (for food and fiber) or co-opt (by converting productive land to other uses) an additional 27%. Thus we have already appropriated about 40% of the terrestrial food supply, leaving only 60% for the other terrestrial plants and animals. You might conclude from this that we are at 40% of the carrying capacity and that the theoretical maximum human population would therefore be 2.5x the current level i.e. 2.5x5.9 = 15 billion, a number that will be reached within the next century if present trends continue. This is the number the earth could support if all of the plant growth on earth were used to support the human population, and if we were not also limited by waste buildup and non-renewable resources. It assumes that we forget about conserving biological diversity for its own sake, forget about preserving any natural habitat, and forget about saving natural ecosystems for the many benefits they provide (like producing oxygen, preventing CO2 buildup, cleansing water supplies, etc.). If we set aside enough of the earth's primary productivity for these other essential purposes, then the predicted carrying capacity for humans is much less than 15 billion; in fact, probably less than the current population.
Another way of looking at global capacity is to examine the degree to which humans already dominate the Earth's ecosystems. Estimates indicate that:
70% of the earth's surface is covered by oceans, and the oceans provide a significant fraction of total primary productivity. Most of the conversion of inorganic compounds (such as carbon dioxide and water) into organic material is done by the phytoplankton: microscopic drifting plants that exist everywhere in the oceans and are the primary source of food for all of the higher levels of the food chain. The phytoplankton gives the ocean its blue/green color, and so measurements of that color can be used to estimate the amount of phytoplankton. This is the rationale behind NASA's Coastal Zone Color Scanner (CZCS) carried on a satellite that was launched in 1978 and worked until 1986. The first image shows cumulative results from imaging over the entire period, and the next image shows results from September 97 to August 98. Green indicates high concentrations, and red indicates very high concentrations of phytoplankton, revealing differences in the productivity of different regions. The North Atlantic and North Pacific are large areas of high productivity, and there are regions of very high productivity along the coasts and at areas of upwelling where extra nutrients are brought to the surface.
Calculations have been done of the amount of Primary Productivity that is required to support fisheries. The results show that humans use about 8% of the primary production of the oceans, but that the fraction is more than 25% for upwelling areas and 35% for temperate continental shelf areas.
Another way to analyze the global situation is
to examine the resources on which we depend and try to estimate how much we can increase
|Fish Catch (million tons)||85||102||20||-10|
|Cropland (million hectares)||1,444||1,516||5||-21|
|Rangeland and Pasture
|Forests (million hectares)||3,413||3,165||-7||-30|
Source: Postel, S. "carrying capacity: Earth's bottom line." State of the World, 1994.
All of these statistics show that we are already stretching these resources to the limit, and that the 33% increase in population will be very difficult to accommodate. The State of Food and Agriculture 1998
The present and predicted increase in human
population is very over the globe.
sq.km. agricultural land
|Former Soviet Union||69||0.7|
Although rapid population growth leads to high rates of habitat loss, some of the greatest pollution problems (both local and global), and high levels of energy use, occur in areas with high densities (Asia and Europe) rather than in countries with high growth rates (Africa and South America).
96% of the projected addition of 3.6 billion people during the period between now and 2030 will occur in the developing nations, where the overall growth rate is 2.1% per year. The fastest growing continent is Africa, which is predicted to double in 23 years; it contains the fastest growing nation, Kenya, with a doubling time of 20 years. The population of Latin America will double in 30 years, and Asia 36 years.
Many regions are already exceeding their carrying capacity; i.e., cannot produce enough food to support their populations. One region where this is very clear is an enormous swath of equatorial Africa called the Sahel, that is undergoing very rapid desertification. The burgeoning populations of this area is contributing to its desertification by clearing forest for agriculture as well as for firewood. In 1900, 40% of Ethiopia was covered by forest; now only 4% is forested.
Sub-Saharan Africa has the highest birth rate, the highest rate of population increase and the lowest use of contraceptives of any major region in the world. The average annual population increase in sub-Saharan Africa is 3 percent, ranging from 2.5 percent to 3.8 percent. But its food supply increases by only 1%. In 12 countries of the region, women have, on average, more than seven children. At current rates, the population of sub-Saharan Africa will double by 2016. The biggest annual increases --more than 3.5 percent --will occur in some of the region's poorest countries: Ivory Coast, Togo, Comoros and Kenya, whose per capita gross national product ranges between $340 and $690 (compared with $22,560 in the United States).
Another area with very rapid population growth is Israeli-occupied Gaza --with a fertility rate of 7.9 children per woman, the highest in the world, and annual population increase of 4 percent, also the world's highest. It is expected to double in population by 2007. Other Middle Eastern countries where women have seven or more children are Iraq, Syria and Yemen.
Rapid population growth has social consequences that have been perfectly clear for at least 30 years. They are low living standards, low education standards, unemployment, starvation, and civil war; these will continue to increase in the developing nations. It also leads to environmental destruction, mainly in the form of deforestation caused by slash-and-burn agriculture, which can only be sustainable at very low population density. This means that the rate of deforestation is going to increase.
The populations of European nations, of North America, and parts of Asia, have all gone through a characteristic series of changes called the demographic transition:
I. Before the transition, both birth and death rates are high, and the growth rate is zero or close to it.
II. In the transitional phase, the birth rate remains high while the death rate declines due to better public health measures (e.g. immunization) and expanded food production due to the improvement of agricultural methods. Population growth is a result of the difference between death rate and birth rate (ignoring immigration and emigration for now), so the decreased death rate leads to a high growth rate.
III. Birth rate begins to decline due to better education, better family planning, more career options for women, and reduced infant mortality which reduces the desire for large families. The growth rate declines, eventually to zero.
(graphics from the Department of Meteorology, University of Maryland College Park)
This is a description of what has happened in presently industrialized nations, and in the 1950's it was accepted as a description of what would inevitably happen to all countries. But in the developing countries (Mexico as an example), the death rate has declined but the birth rate has stayed high. In these agrarian countries, large family sizes are needed to supply the farm labor. The social and economic changes that could lower the birth rate have not happened.
In many developing countries, the populations will probably stabilize not because of a decrease in the birth rate, but a return to higher death rates, and this will reflect mainly an increase in the number of children dying from starvation-related causes. Over 40% of deaths in India are of children under four years old.
The U.S. is at an early stage in a demographic transition. The growth rate has slowed to 0.7% per year although we are still the fastest-growing industrialized nation. The death rate has been reduced substantially but this has not yet been compensated by a big enough decline in birth rate. About half of our population growth is from immigration, higher than in any other nation. Teenage pregnancy rates have been soaring, both on a nationwide level and in Orange County.
Different countries have different population structures, leading to two different types of problem: The population increase in the less-developed countries will be largely in the reproductive age classes. Even if average family sizes were brought down dramatically in the near future, the population will still increase substantially as the huge pre-adult population in the developing world reaches child-bearing age and reproduces. These are also the people that need jobs.
A different problem faces the developed countries: the increase is in the older age groups, especially those that are beyond employable age. The number of people over 100 years old in this country was 4,000 in 1970; 64,000 in 1990, and is projected to be 1.4 million in 2040.
Visit Population Pyramids and ask for dynamic population pyramids for any country. Compare Mexico, Sweden and the U.S.
The widening gap in the distribution of income is a major cause of environmental decline. In 1960, the richest 20% of the world's people absorbed 70% of global income; by 1989 their share had increased to 83%. Over the same period, the poorest 20% saw their share of global income decrease from 2.3% to 1.4%. The ratio of the richest fifth's share to the poorest fifth's share rose from 30 to 59 over this period. The rich really do get richer and the poor get poorer.
The inequality of income distribution is bad for the environment for two reasons: it encourages excess consumption, waste and pollution at the rich end of the spectrum and it perpetuates poverty at the poor end. Both categories of the population are more likely than those in the middle to do serious ecological damage - the rich because of their high consumption of energy, raw materials, and manufactured goods, and the poor because they are often forced to cut down forest, grow crops and graze cattle in order to subsist on the land.
A similar picture emerges at the national level. The rich
countries have a large per capita impact on the environment because of their high rate of
consumption and waste. The U.S., with only 4.7 percent of the world's population,
consumes 25 percent of the world's resources and generates 25 to 30 percent of the world's
waste. Compared to an average citizen in India, a typical person in the U.S. uses:
50 times more steel
56 times more energy
170 times more synthetic rubber and newsprint
250 times more motor fuel
300 times more plastic
Each American consumes as much grain as five Kenyans, and as much energy as 35 Indians, 150 Bangladeshis (a whole village!) or 500 Ethiopians.
Paul Ehrlich has suggested that we should measure the environmental impact of populations not simply as a function of the number of people but by using the equation I (environmental impact) = P x A x T, where P is the size of the Population, A is Affluence (or consumption), and T is a measure of how environmentally malign are the Technologies and the economic, social, political and political arrangements involved in servicing the consumption. Mainly because of the high level of "T", the population growth in the United States is more serious for the environment than anywhere else in the world.
Many countries (newly industrialized countries) have become much more industrialized since World War II, and this has allowed them to greatly increase their standards of living. But this has been at enormous ecological costs, mainly in other countries. Japan, economically very successful and with a very high population density (331/sq.km.) has only 1/7 the world average of cropland per capita. So it imports 3/4 of its grain and 2/3 of its wood. It is now the world's largest net importer of forest products. The Netherlands, to meet its need for food and fiber, relies on importing the products of about 10 times its own area of cropland, pasture and forest. These countries, and many other industrialized countries, have far exceeded their own internal carrying capacity and must rely on other nations to provide food.
There is nothing wrong in principle with one nation selling its agricultural and forestry products, and other nations selling their manufactured goods. However, many developing countries would like to emulate the industrialized nations and increase their standard of living. But it is not possible for all countries to exceed their carrying capacities and convert to manufacturing.
The United Nations has for over forty years been coordinating efforts to bring global population growth under control.
At the U.N. Conference on Population in Cairo in 1994, 179 nations endorsed a new "Programme of Action" that called on governments to provide universal access to reproductive health care by 2015 as a global human rights imperative. Instead of focusing just on controlling population growth (an approach which was not very effective) this program tries to identify and deal with the many interrelated social problems that contribute to population growth and poverty. The conference recognized that meeting individual reproductive health needs would enable couples to choose the number and spacing of their children, and that this would lead to smaller families and stabilization of the human population.
The goal of the Cairo agreement is to stabilize human population at 7.8 billion by 2050. There are five basic components:
The United Nations Population Fund (UNFPA) is the main international source of population assistance to developing countries. It is funded by voluntary contributions from member countries. The Fund supports Programs to improve pre- and post-natal mother's health, to provide access to voluntary family planning programs and contraception, to support education on sexually transmitted diseases and HIV, and to formulate population policies that support sustainable development and poverty eradication. The fund helps to reduce unwanted pregnancies, abortions, and deaths and injuries for millions of mothers around the world.
U.S. funding for UNFPA has been withheld for many years because of the agency's support of Chinas policies (in 1983, the peak year for abortions in China, UNFPA presented China's family planning minister with the U.N. Population Award). In 2002 President George W. Bush decided to withhold the $34 million that both houses of Congress had agreed to give to the agency, arguing that UNFPA gives tacit support to China's one-child policy just by working in China. The U.S. is the only country ever to deny funding to UNFPA for non-budgetary reasons. UNFPA estimates that the loss of U.S. support could result in 2 million unwanted pregnancies, nearly 800,000 abortions, 4,700 maternal deaths and 77,000 infant and child deaths.
China's population in 2002 was estimated at 1.28 billion people, which is five times higher than that of the U.S. and over 20% of the worlds total. Its land area is slightly less than that of the U.S., but only 10% of it is arable compared to 19% in the U.S.
In China, a "one-child-per-couple" policy has been in effect since 1979, with the (unmet) goal of limiting the nation's population to 1.2 billion by the year 2000. The policy includes rewards for having only one child including monetary grants, additional maternity leave, and increased land allocations for farmers. The children of these couples are also given preferential treatment in education, housing, and employment. The policy allows couples to have a second child only under rare circumstances, and does not allow more than two children.
After her first child is born, a woman is required to wear an intrauterine device, and removal of this device is considered a crime. Otherwise, one of the parents must be sterilized. Physicians receive a bonus whenever they perform a sterilization. Couples are punished for refusing to terminate unapproved pregnancies, for giving birth when under the legal marriage age, and until recently they were punished for having a second child. The penalties include fines, loss of land grants, food, loans, farming supplies, benefits, jobs and discharge from the Communist Party. In some provinces the fines can be up to 50% of a couple's annual salary.
In many provinces sterilization is required after the couple has had two children.
The one-child-per-couple policy was strictly enforced during the early 1980's. The coercive measures peaked in 1983, when 14.4 million abortions were performed (for comparison, there were 19 million live births in that year). Because of strong public resistance, the Chinese government moderated its stance in the late 1980's and tried instead to emphasize public education and good public relations with the people. Because the birth rate started to climb again, the government tightened up its family planning guidelines in 1987 and 1989. In 2001, a new law was passed to reinforce and standardize the one-child policy over the entire country. It includes incentives for compliance but no longer requires fines to be imposed for couples who have a second child.
China's population policy has brought the average number of children per woman down from 5.01 in 1970 to 1.84 in 1995. But the Chinese population is still growing. This is because the children born during the previous period of high fertility are having children -- albeit fewer per couple -- of their own. China did not achieve its goal of stabilizing population at 1.2 billion in the year 2000. Instead, it grew to 1.3 billion in 2000 and will inevitably increase to about 1.5 billion by 2025.
In India, where family-planning efforts have been less aggressive, the population is growing much faster. With 947 million inhabitants today, India may overtake China as the world's most populous nation, surpassing the 2 billion mark in 2025.
In 1999 the Worldwatch Institute reported that rising death rates are slowing world population growth for the first time since famine killed 30 million people in China in 1959-61. Partly because of these rising death rates, the U.N. revised its estimate for world population in 2025 from 9.4 to 8.9 billion. Three factors are pushing the death rates up, especially in sub-Saharan Africa and the Indian sub-continent:
Cohen, J.E. (1995) How Many People can the Earth Support? W. W. Norton, N.Y. 532p.
Brown, L. R. (1995) Who Will Feed China? : Wake-Up Call for a Small Planet. The Worldwatch Environmental Alert
Humans altering Earth for the worse | Scientists warn of mass extinction | World population continues to grow | ZPG takes to the airwaves | Wal-Mart bans emergency contraceptive | Zero Population Growth | Population Education | Facing the Future: People and the Planet