By the reckoning of my fellow demographers, human population first reached the billion in the early 19th century. But it took little more than another hundred years for that figure to climb to two billion in 1930, and by 1975 the number doubled again. In the remaining years of this century world population will top six billion; by 2025, eight billion.
The lion's share of this increase will occur in the emerging nations, already home to most of mankind, and will be concentrated in cities overburdened by their current populations. Advances in technology and medicine that allow us longer, healthier lives have buoyed population size and growth rate – and thus created challenges of magnitudes the world has never before faced.
Urban authorities worldwide are declaring their regions to be in crisis situations with drastic shortcomings in housing, water, sewage, transportation, and job opportunities. Lagos, Nigeria, for example, with some five million people and one of the world's' highest growth rates, has so far been unsuccessful in planning construction of a citywide sewer system.
Urban areas in developing countries are haphazardly spreading far beyond traditional boundaries to accommodate natural population increase and rural migration. Industrial and residential uses and speculation often take over valuable farmland. On the edges of Cairo, prime agricultural land is being lost to the destructive stripping of topsoil for brick making.
Rapid population growth and urbanization will continue into the foreseeable future, with bleak consequences. Conditions today are only the opening scenes of a drama in which Third World cities, now home to more than one billion people, will hold nearly four billion residents by 2025. The urbanization trend in developing nations
Only seven urban centres held more than five million in 1950: New York, London, Paris, Germany's Rhein-Ruhr complex, Tokyo-Yokohama, Shanghai, and Buenos Aires. 'Labour supply and demand had grown in unison as these centres evolved over decades, if not centuries. The enduring architecture of London and Paris reflects slow, graceful development.
Today 34 cities boast more than five million residents. By 2025, the UN projects, there will be 93, and 80 of these will be in the emerging nations. Leisurely development and a low to moderate population growth rate are luxuries of the past.The upsurge in Third World urban populations has overwhelmed resources. Sprawling slums, massive traffic jams, chronic unemployment, regular failure of electric and water services, strained educational and recreational facilities, and skyrocketing food and fuel costs are the stuff of daily existence.
Though demographers warned that the population of Mexico City would double during the 1970s, few others believed such a rise could occur. Yet the metropolis did grow from 8 million to 14 million people, and it may reach 30 million by 2010. Similar projections for other developing nations are now being accepted as realistic. The paradox of population growth
For most of mankind's history world population grew slowly, checked by epidemics, famine, and chronic malnutrition. Though the mortality rate was high, the birth rate was slightly higher, and with that small excess our numbers gradually increased.
Human population grows much like a savings account accruing compound interest – greater amounts yield greater amounts. English economist Thomas Malthus cited this fact in his 1798 "Essay on the Principal of Population," warning that human numbers – if unchecked – would soon outweigh the ability of the earth to feed them.
But Malthus was writing on the eve of a new era, when the industrial revolution would transform Europe. The continent's population did rise substantially during the 19th century as medical breakthroughs towered the death rate, but simultaneous agricultural advances also allowed food production to rise. And emigration to America helped siphon off population excess.
The newly widened gap between birth and death rates gradually began to close as smaller families become socially acceptable. That trend quickened in industrialized countries during the 20th century, and today the gap between births and deaths is once again small.
In the developing countries a far different history prevails. Only in the 1930s did the death rate begin to fall. but it fell dramatically as imported technology improved overall health and dietary conditions. The birth rate, however, remained high. Its decline depends largely on changing cultural norms, and family planning has made substantial inroads only within the past two decades. As the gap between deaths and births widened, the population exploded. Generally speaking, there were not more births – there were more survivors.With this considerable momentum, population expansions in these countries will continue. Even optimistic scenarios do not foresee a levelling off of growth until late in the 21st century.
Because the traditional birth-and-death-rate relationship has been broken in Third World countries only within the past few decades, they now hold very youthful populations, and the populations will continue to soar because there are more women of childbearing age. Hence the paradox of modern population growth: even as the birth rate continues to fall, the population will rise.
For every 100 Africans today, 55 are under 20 years of age. Among Europeans only 30 out of 100 are under 20. In 1975, 93 million African women were of childbearing age. The birth rate that year in Africa was 47 per 1,000, and 19 million children were born. The UN projects that by 2025 the African birth rate will fall to 25 per 1,000 - a reduction of almost half. But by then the number of reproductive-age women will have risen to 430 million, and even with a lowered birth rate 42 million children will enter the world that year. A clouded crystal ball
How many people can the earth hold? Will birth and death rates continue to decline? Can food production keep apace of population growth? Can technology supplement or replace today's resources? What are the long-term effects of pollution on health, climate, and farm production?
Debate over such issues has spawned volumes, as scholars look to the future with varying degrees of optimism and gloom. In a lecture titled "The Terror of Change," Patricia Gulas Strauch cited three aspects of our future about which there is little disagreement: The speed of change will accelerate, the world will be increasingly complex, and nations and world issues will be increasingly interdependent.
The problem facing Third World megacities cannot be ignored by developed countries. We cannot look to the past for solutions; there is no precedent for such growth. We are in uncharted, challenging waters.
Answer the questions:
What are the reasons of the population growth?
What may be the consequences of the population growth?