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تاريخ التسجيل : 25/08/2008
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مُساهمةموضوع: lllllllllllllll   السبت فبراير 13, 2010 4:36 pm

The Demographic transition model (DTM):
Is a model used to represent the process of explaining the transformation of countries from high birth rates and high death rates to low birth rates and low death rates as part of the economic development of a country from a pre-industrial to an industrialized economy. It is based on an interpretation begun in 1929 by the American demographer Warren Thompson [1] of prior observed changes, or transitions, in birth and death rates in industrialized societies over the past two hundred years.
Most developed countries are beyond stage three of the model; the majority of developing countries are in stage 2 or stage 3. The model was based on the changes seen in Europe so these countries follow the DTM relatively well. Many developing countries have moved into stage 3. The major (relative) exceptions are some poor countries, mainly in sub-Saharan Africa and some Middle Eastern countries, which are poor or affected by government policy or civil strife, notably Pakistan, Palestinian Territories, Yemen and Afghanistan.[2]
Note that this model predicts ever decreasing fertility rates, whereas recent data shows that after a certain level of development the fertility increases again.
Contents
• 1 Summary of the theory
• 2 Stage One
• 3 Stage Two
• 4 Stage Three
• 5 Stage Four
• 6 Stage Five
• 7 Effects on age structure
• 8 Critical evaluation
o 8.1 Non-applicability to less-developed countries
o 8.2 Economic development not sufficient cause to effect demographic change
o 8.3 Application to the U.S. in the 19th and 20th centuries
• 11 References





Summary of the theory


Population pyramids for 4 stages of the model


Demographic change in Sweden from 1735 to 2000.
Red line: crude death rate (CDR), blue line: (crude) birth rate (CBR)
The transition involves four stages, or possibly five.
• In stage one, pre-industrial society, death rates and birth rates are high and roughly in balance.
• In stage two, that of a developing country, the death rates drop rapidly due to improvements in food supply and sanitation, which increase life spans and reduce disease. These changes usually come about due to improvements in farming techniques, access to technology, basic healthcare, and education. Without a corresponding fall in birth rates this produces an imbalance, and the countries in this stage experience a large increase in population.
• In stage three, birth rates fall due to access to contraception, increases in wages, urbanization, a reduction in subsistence agriculture, an increase in the status and education of women, a reduction in the value of children's work, an increase in parental investment in the education of children and other social changes. Population growth begins to level off.
• During stage four there are both low birth rates and low death rates. Birth rates may drop to well below replacement level as has happened in countries like Germany, Italy, and Japan, leading to a shrinking population, a threat to many industries that rely on population growth. As the large group born during stage two ages, it creates an economic burden on the shrinking working population. Death rates may remain consistently low or increase slightly due to increases in lifestyle diseases due to low exercise levels and high obesity and an aging population in developed countries.
As with all models, this is an idealized picture of population change in these countries. The model is a generalization that applies to these countries as a group and may not accurately describe all individual cases. The extent to which it applies to less-developed societies today remains to be seen. Many countries such as China, Brazil and Thailand have passed through the DTM very quickly due to fast social and economic change. Some countries, particularly African countries, appear to be stalled in the second stage due to stagnant development and the effect of AIDS.

Stage One
In pre-industrial society, death rates and birth rates were both high and fluctuated rapidly according to natural events, such as drought and disease, to produce a relatively constant and young population. Children contributed to the economy of the household from an early age by carrying water, firewood, and messages, caring for younger siblings, sweeping, washing dishes, preparing food, and working in the fields.[4]
Raising a child cost little more than feeding him; there were no education or entertainment expenses and, in equatorial Africa, there were no clothing expenses either. Thus, the total cost of raising children barely exceeded their contribution to the household. In addition, as they became adults they become a major input to the family business, mainly farming, and were the primary form of insurance for adults in old age. In India, an adult son was all that prevented a widow from falling into destitution. While death rates remained high there was no question as to the need for children, even if the means to prevent them had existed.[5]
Stage Two


World population 10,000 BC - 2000 AD
This stage leads to a fall in death rates and an increase in population.[6] The changes leading to this stage in Europe were initiated in the Agricultural Revolution of the 18th century and were initially quite slow. In the 20th century, the falls in death rates in developing countries tended to be substantially faster. Countries in this stage include Yemen, Afghanistan, the Palestinian territories, Bhutan and Laos and much of Sub-Saharan Africa (but do not include South Africa, Zimbabwe, Botswana, Swaziland, Lesotho, Namibia, Kenya and Ghana, which have begun to move into stage 3).[7]
The decline in the death rate is due initially to two factors:
• First, improvements in the food supply brought about by higher yields in agricultural practices and better transportation prevent death due to starvation and lack of water. Agricultural improvements included crop rotation, selective breeding, and seed drill technology.
• Second, significant improvements in public health reduce mortality, particularly in childhood. These are not so much medical breakthroughs (Europe passed through stage two before the advances of the mid-20th century, although there was significant medical progress in the 19th century, such as the development of vaccination) as they are improvements in water supply, sewerage, food handling, and general personal hygiene following from growing scientific knowledge of the causes of disease and the improved education and social status of mothers.
A consequence of the decline in mortality in Stage Two is an increasingly rapid rise in population growth (a "population explosion") as the gap between deaths and births grows wider. Note that this growth is not due to an increase in fertility (or birth rates) but to a decline in deaths. This change in population occurred in northwestern Europe during the 19th century due to the Industrial Revolution. During the second half of the 20th century less-developed countries entered Stage Two, creating the worldwide population explosion that has demographers concerned today.


Angola 2005
Another characteristic of Stage Two of the demographic transition is a change in the age structure of the population. In Stage One, the majority of deaths are concentrated in the first 5–10 years of life. Therefore, more than anything else, the decline in death rates in Stage Two entails the increasing survival of children and a growing population. Hence, the age structure of the population becomes increasingly youthful and more of these children enter the reproductive cycle of their lives while maintaining the high fertility rates of their parents. The bottom of the "age pyramid" widens first, accelerating population growth. The age structure of such a population is illustrated by using an example from the Third World today.
Stage Three
Stage Three moves the population towards stability through a decline in the birth rate.[8] There are several factors contributing to this eventual decline, although some of them remain speculative:
• In rural areas continued decline in childhood death means that at some point parents realize they need not require so many children to be born to ensure a comfortable old age. As childhood death continues to fall and incomes increase parents can become increasingly confident that fewer children will suffice to help in family business and care for them in old age.
• Increasing urbanization changes the traditional values placed upon fertility and the value of children in rural society. Urban living also raises the cost of dependent children to a family. A recent theory suggests that urbanization also contributes to reducing the birth rate because it disrupts optimal mating patterns. A 2008 study in Iceland found that the most fecund marriages are between distant cousins. Genetic incompatibilities inherent in more distant outbreeding makes reproduction harder.[9]
• In both rural and urban areas, the cost of children to parents is exacerbated by the introduction of compulsory education acts and the increased need to educate children so they can take up a respected position in society. Children are increasingly prohibited under law from working outside the household and make an increasingly limited contribution to the household, as school children are increasingly exempted from the expectation of making a significant contribution to domestic work. Even in equatorial Africa, children now need to be clothed, and may even require school uniforms. Parents begin to consider it a duty to buy children books and toys. Partly due to education and access to family planning, people begin to reassess their need for children and their ability to raise them.[5]


A major factor in reducing birth rates in stage 3 countries such as Malaysia is the availability of family planning facilities, like this one in Kuala Terenganu, Terenganu, Malaysia.
• Increasing female literacy and employment lower the uncritical acceptance of childbearing and motherhood as measures of the status of women. Working women have less time to raise children; this is particularly an issue where fathers traditionally make little or no contribution to child-raising, such as southern Europe or Japan. Valuation of women beyond childbearing and motherhood becomes important.
• Improvements in contraceptive technology are now a major factor. Fertility decline is caused as much by changes in values about children and sex as by the availability of contraceptives and knowledge of how to use them.
The resulting changes in the age structure of the population include a reduction in the youth dependency ratio and eventually population aging. The population structure becomes less triangular and more like an elongated balloon. During the period between the decline in youth dependency and rise in old age dependency there is a demographic window of opportunity that can potentially produce economic growth through an increase in the ratio of working age to dependent population; the demographic dividend.
However, unless factors such as those listed above are allowed to work, a society's birth rates may not drop to a low level in due time, which means that the society cannot proceed to Stage Four and is locked in what is called a demographic trap.
Countries that have experienced a fertility decline of over 40% from their pre-transition levels include: Costa Rica, El Salvador, Panama, Jamaica, Mexico, Colombia, Ecuador, Guyana, Surinam, Philippines, Indonesia, Malaysia, Sri Lanka, Turkey, Azerbaijan, Turkmenistan, Uzbekistan, Egypt, Tunisia, Algeria, Morocco, Lebanon, South Africa, India, Saudi Arabia, and many Pacific islands.
Countries that have experienced a fertility decline of 25-40% include: Honduras, Guatemala, Nicaragua, Paraguay, Bolivia, Vietnam, Myanmar, Bangladesh, Tajikistan, Jordan, Qatar, Albania, United Arab Emirates, Zimbabwe, and Botswana.
Countries that have experienced a fertility decline of 10-25% include: Haiti, Papua New Guinea, Nepal, Pakistan, Syria, Iraq, Libya, Sudan, Kenya, Ghana and Senegal.[7]
STAGE 3

Stage Four
This occurs where birth and death rates are both low. Therefore the total population is high and stable.[10] Some theorists consider there are only 4 stages and that the population of a country will remain at this level. The DTM is only a suggestion about the future population levels of a country. It is not a prediction.
Countries that are at this stage (Total Fertility Rate of less than 2.5 in 1997) include: United States, Canada, Argentina, Australia, New Zealand, most of Europe, Bahamas, Puerto Rico, Trinidad and Tobago, Brazil, Sri Lanka, South Korea, Singapore, Iran, China, Turkey, North Korea, Thailand and Mauritius.[7]
Stage Five
See also: Aging of Europe and Aging of Japan


United Nation's population projections by location.
Note the vertical axis is logarithmic & is millions of people.
The original Demographic Transition model has just four stages; however, some theorists consider that a fifth stage is needed to represent countries that have sub-replacement fertility. Most European and many East Asian countries now have higher death rates than birth rates.
There may be a further stage of demographic development. In an article in the August 2009 issue of Nature, Myrskyla, Kohler and Billari show that previously negative relationship between national wealth (as measured by the human development index (HDI) and birth rates has become J-shaped. Development promotes fertility decline at low and medium HDI levels, but advanced HDI promotes a rebound in fertility.[11] In many countries with very high levels of development (around 0.95) fertility rates are now approaching two children per woman - although there are exceptions, notably Canada and Japan.[12]







Effects on age structure
The decline in death rate and birth rate that occurs during the demographic transition leads to a radical transformation of the age structure. When the death rate declines during the second stage of the transition, the result is primarily an increase in the child population. The reason is that when the death rate is high (stage one), the infant mortality rate is very high, often above 200 deaths per 1000 children born. When the death rate falls or improves, this, in general, results in a significantly lower infant mortality rate and, hence, increased child survival. Over time, as cohorts increased by higher survival rates get older, there will also be an increase in the number of older children, teenagers, and young adults. This implies that there is an increase in the fertile population which, with constant fertility rates, will lead to an increase in the number of children born. This will further increase the growth of the child population. The second stage of the demographic transition, therefore, implies a rise in child dependency.
Critical evaluation
It has to be remembered that the DTM is only a model and cannot necessarily predict the future. It does however give an indication of what the future birth and death rates may be for an underdeveloped country, together with the total population size. Most particularly, of course, the DTM makes no comment on change in population due to migration. It is not applicable for high levels of development, as it has been shown that after a HDI of 0.9 the fertility increases again [13].
Non-applicability to less-developed countries
DTM has a questionable applicability to less economically developed countries (LEDCs), where wealth and information access are limited. For example, the DTM has been validated primarily in Europe, Japan and North America where demographic data exists over centuries, whereas high quality demographic data for most LDCs did not become widely available until the mid 20th century.[14] DTM does not account for recent phenomena such as AIDS; in these areas HIV has become the leading source of mortality. Some trends in waterborne bacterial infant mortality are also disturbing in countries like Malawi, Sudan and Nigeria; for example, progress in the DTM clearly arrested and reversed between 1975 and 2005.[15]
Economic development not sufficient cause to effect demographic change
DTM assumes that population changes are induced by industrial changes and increased wealth, without taking into account the role of social change in determining birth rates, e.g., the education of women. In recent decades more work has been done on developing the social mechanisms behind it.[2]
DTM assumes that the birth rate is independent of the death rate. Nevertheless, demographers maintain that there is no historical evidence for society-wide fertility rates rising significantly after high mortality events. Notably, some historic populations have taken many years to replace lives such as the Black Death.
Some have claimed that DTM does not explain the early fertility declines in much of Asia in the second half of the 20th century or the delays in fertility decline in parts of the Middle East. Nevertheless, the demographer John C Caldwell has suggested that the reason for the rapid decline in fertility in some developing countries compared to Western Europe, the United States, Canada, Australia and New Zealand is mainly due to government programs and a massive investment in education both by governments and parents.[7]
Application to the U.S. in the 19th and 20th centuries
A simplification of the DTM theory proposes an initial decline in mortality followed by a later drop in fertility. The changing demographics of the U.S. in the last two centuries did not parallel this model. Beginning around 1800, there was a sharp fertility decline; at this time, an average woman usually produced seven births per lifetime, but by 1900 this number had dropped to nearly four. A mortality decline was not observed in the U.S. until almost 1900—a hundred years following the drop in fertility.
However, this late decline occurred from a very low initial level. It's been estimated that the crude death rate in 17th century rural New England was already as low as 20 deaths per 1000 residents per year (levels of up to 40 per 1000 being typical during stages one and two). The phenomenon is explained by the pattern of colonization of the United States: high death rates unavoidably had to match high birth rates in densely populated Europe, whereas, in the United States, westward expansion of the frontier into sparsely populated interior allowed ample room to absorb all the excess people, resulting in exponential population growth (from less than 4 million people in 1790, to 23 million in 1850, to 76 million in 1900.)
Today, the U.S. is recognized as having both low fertility and mortality rates. Specifically, birth rates stand at 14 per 1000 per year and death rates at 8 per 1000 per year.[16]










References
1. ^ "Warren Thompson". Encyclopedia of Population. 2. Macmillan Reference. 2003. pp. 939–940. ISBN 0-02-865677-6.
2. ^ a b Caldwell, John C.; Bruce K Caldwell, Pat Caldwell, Peter F McDonald, Thomas Schindlmayr (2006). Demographic Transition Theory. Dordrecht, The Netherlands: Springer. pp. 418. ISBN 1-4020-4373-2.,p239
3. ^ "Advances in development reverse fertility declines". Nature. 6 August 2009. http://www.nature.com/nature/journal/v460/n7256/abs/nature08230.html.
4. ^ Barcelona fieldwork
5. ^ a b Caldwell (2006), Chapter 5
6. ^ BBC bitesize
7. ^ a b c d Caldwell (2006), Chapter 10
8. ^ Marathon geography
9. ^ "Kissing cousins, missing children". The Economist 7 February 2008.
10. ^ Main vision
11. ^ Myrskyla, M., Kohler, H-P., and Billari, F. Advances in development reverse fertility declines. Nature 460, 741-743 (6 August 2009).
12. ^ "The best of all possible worlds?" The Economist 6 August 2009.
13. ^ "Advances in development reverse fertility declines". Nature. 6 August 2009. http://www.nature.com/nature/journal/v460/n7256/abs/nature08230.html.
14. ^ Ronald Lee, The Demographic Transition: Three Centuries (2003)
15. ^ Nigeria: Reversal of Demographic Transition
16. ^World factbook

Advances in development reverse fertility declines

During the twentieth century, the global population has gone through unprecedented increases in economic and social development that coincided with substantial declines in human fertility and population growth rates1, 2. The negative association of fertility with economic and social development has therefore become one of the most solidly established and generally accepted empirical regularities in the social sciences1, 2, 3. As a result of this close connection between development and fertility decline, more than half of the global population now lives in regions with below-replacement fertility (less than 2.1 children per woman)4. In many highly developed countries, the trend towards low fertility has also been deemed irreversible5, 6, 7, 8, 9. Rapid population ageing, and in some cases the prospect of significant population decline, have therefore become a central socioeconomic concern and policy challenge10. Here we show, using new cross-sectional and longitudinal analyses of the total fertility rate and the human development index (HDI), a fundamental change in the well-established negative relationship between fertility and development as the global population entered the twenty-first century. Although development continues to promote fertility decline at low and medium HDI levels, our analyses show that at advanced HDI levels, further development can reverse the declining trend in fertility. The previously negative development–fertility relationship has become J-shaped, with the HDI being positively associated with fertility among highly developed countries. This reversal of fertility decline as a result of continued economic and social development has the potential to slow the rates of population ageing, thereby ameliorating the social and economic problems that have been associated with the emergence and persistence of very low fertility.

















SOURCE : http://family.jrank.org/

The relatively permanent movement of people across territorial boundaries is referred to as inmigration and out-migration, or immigration and emigration when the boundaries crossed are international. The place of in-migration or immigration is called the receiver population, and the place of out-migration or emigration is called the sender population. There are two basic types of migration studied by demographers:
• Internal migration. This refers to a change of residence within national boundaries, such as between states, provinces, cities, or municipalities. An internal migrant is someone who moves to a different administrative territory.
• International migration. This refers to change of residence over national boundaries. An international migrant is someone who moves to a different country. International migrants are further classified as legal immigrants, illegal immigrants, and refugees. Legal immigrants are those who moved with the legal permission of the receiver nation, illegal immigrants are those who moved without legal permission, and refugees are those crossed an international boundary to escape persecution.
Jay Weinstein and Vijayan Pillai (2001) denote a third classification: forced migration. Forced migration exists when a person is moved against their will (slaves), or when the move is initiated because of external factors (natural disaster or civil war). The distinction between internal and international migration is crucial because they happen for different reasons. Because structural barriers are more likely to impede the mobility of a potential international migrant than an internal migrant—international migration involves more administrative procedures, greater expense, and more difficulties associated with obtaining employment, accessing state services, learning a new language, and the like—the motivations behind international migration are usually stronger than those behind internal migration (Weeks 1999).





Migration - Theories of Migration

People move for different reasons. These differences affect the overall migration process. The conditions under which a migrant enters a receiver population can have broad implications for all parties involved. The expression migration experience refers to the fact that different causes for migration will produce different outcomes observable from a sociological perspective. For example, a person who moves within a nation will not have the same migration experience as a political refugee. In most cases, refugees need special services from the receiver population such as emergency shelter, food, and legal aid. The psychological trauma of fleeing their homeland and leaving family members behind can also complicate refugees' adjustment to their new environment. Considering that a migrant can be a slave, refugee, or job-seeker, or have some other reason for moving, no single theory can provide a comprehensive explanation for the migration process.
Although a comprehensive theory is unattainable, it remains a crucial task of demographers to explain why people migrate. Theories of migration are important because they can help us understand population movements within their wider political and economic contexts. For example, if outmigration from Third World nations is shown to be a result of economic problems caused by the global economy, then such migration could be managed with better international economic agreements instead of restrictive immigration acts. Indeed, rather than slowing Mexican in-migration to the United States, termination of the bracero program actually increased the amount of illegal immigration because it exacerbated Mexican poverty.
Ernest Ravenstein is widely regarded as the earliest migration theorist. Ravenstein, an English geographer, used census data from England and Wales to develop his "Laws of Migration" (1889). He concluded that migration was governed by a "push-pull" process; that is, unfavorable conditions in one place (oppressive laws, heavy taxation, etc.) "push" people out, and favorable conditions in an external location "pull" them out. Ravenstein's laws stated that the primary cause for migration was better external economic opportunities; the volume of migration decreases as distance increases; migration occurs in stages instead of one long move; population movements are bilateral; and migration differentials (e.g., gender, social class, age) influence a person's mobility.
Many theorists have followed in Ravenstein's footsteps, and the dominant theories in contemporary scholarship are more or less variations of his conclusions. Everett Lee (1966) reformulated Ravenstein's theory to give more emphasis to internal (or push) factors. Lee also outlined the impact that intervening obstacles have on the migration process. He argued that variables such as distance, physical and political barriers, and having dependents can impede or even prevent migration. Lee pointed out that the migration process is selective because differentials such as age, gender, and social class affect how persons respond to push-pull factors, and these conditions also shape their ability to overcome intervening obstacles. Furthermore, personal factors such as a person's education, knowledge of a potential receiver population, family ties, and the like can facilitate or retard migration.
Several theories have been developed to treat international patterns of migration on their own terms, but these too are variants of push-pull theory. First, neoclassical economic theory (Sjaastad 1962; Todaro 1969) suggests that international migration is related to the global supply and demand for labor. Nations with scarce labor supply and high demand will have high wages that pull immigrants in from nations with a surplus of labor. Second, segmented labor-market theory (Piore 1979) argues that First World economies are structured so as to require a certain level of immigration. This theory suggests that developed economies are dualistic: they have a primary market of secure, well-remunerated work and a secondary market of low-wage work. Segmented labor-market theory argues that immigrants are recruited to fill these jobs that are necessary for the overall economy to function but are avoided by the native-born population because of the poor working conditions associated with the secondary labor market. Third, world-systems theory (Sassen 1988) argues that international migration is a by-product of global capitalism. Contemporary patterns of international migration tend to be from the periphery (poor nations) to the core (rich nations) because factors associated with industrial development in the First World generated structural economic problems, and thus push factors, in the Third World.


Migration - Migration And The Global Economy

Before the international economic downturns that began in the 1970s, the composition of international migration generally held to Ravenstein's hypothesis that the primary motivation for migration was economic, and that young males predominated long-distance travel. Since the 1970s, the pattern of migration has transformed with global economic changes. Moreover, the composition of migration streams transformed because earlier waves of migration created support networks that helped more recent migrants overcome intervening obstacles and difficulties associated with adjusting to a new environment (Boyd 1989). As people settled in new places, they became valuable sources of information and economic assistance for prospective migrants to draw upon. As Monica Boyd (1989) notes, while structural forces form the basic incentives for migration, push-pull factors are filtered through social networks that connect sender and receiver populations. Various patterns of migration (e.g., Mexican immigration to the United States) have become institutionalized as these networks took root.
However, while family contacts often determine where migrants move, structural forces remain powerful causal factors. Douglas Massey and colleagues (1994) point out that most empirical evidence suggests that a crucial impetus for international migration is the combination of systemic unemployment in the sender population and good employment prospects in the receiver population. World-systems theorists argue that one effect of globalization has been to keep Third World economies dependent on agriculture and the exportation of raw materials and simple commodities. Slow industrialization and relatively high fertility rates have generated acute unemployment in these nations, and this partially explains why net migration streams have generally flowed in a unilateral (from periphery to core nations) under the global economy. Economic problems associated with globalization have made labor migration an important survival strategy for many Third World families. For some nations labor has become a major export economy, and states have facilitated migration to capitalize on its economic benefits. Shu-Ju Cheng (1999) notes that there were over two million documented Filipino migrant workers worldwide by 1995, and they remitted U.S. $18 billion between 1975 and 1994. Massey and colleagues (1994) point out that Mexican remittances were so great in certain communities that there were more U.S. dollars in circulation than their peso equivalent. In 1995, the total of world remittances from migrant laborers amounted to U.S. $70 billion (Taylor 1999).
Migration connections between rural economies and urban and international labor markets are particularly important for Third World consumption and production. Out-migration from rural populations to external labor markets has stimulated consumption and productivity in many Third World countries. As Massey and colleagues (1994) note, one study of two Mexican rural communities showed that remittances from domestic urban centers and the United States sustained a level of consumption 37 percent higher than gross production therein. J. Edward Taylor (1999) remarks that for every dollar Mexican migrant laborers sent home from the United States, Mexico's Gross National Product (GNP) increased between $2.69 and $3.17. Contrary to neoclassical theory, these studies demonstrate the potential nonunitary impact of labor migration. Besides increasing household consumption, income transfers have had a dynamic impact on some Third World economies. Remittances often initiate economic improvements because they are used for productive investments, and thus increase household incomes, productivity, and the GNP.









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التحول الديموغرافي

يقصد بالتحول الديموغرافي « الانتقال من حالة ارتفاع معدلات الخصوبة والوفاة إلى انخفاض معدلات الخصوبة والوفاة » . ويمر هذا التحول بمرحلتين : الأولى ينخفض فيها معدل وفيات الأطفال والرضع .، بينما يستمر معدل الخصوبة مرتفعاً ، فيرجع معدل النمو السكاني وترتفع نسبة الفئات العمرية الصغيرة ويرتفع معدل الإعالة أما المرحلة الثانية فينخفض فيها معدل الخصوبة تدريجياً حتى يبلغ معدل الإحلال (2.11 طفل لكل امرأة ) فينخفض معدل النمو السكاني ويتجه نحو الاستقرار وتنخفض نسبة الفئات العمرية الصغيرة ، وترتفع نسبة السكان في سن العمل ، الذين كانوا في الفئات العمرية الصغيرة في المرحلة الأولى ، وينخفض معدل الإعالة ، وان كان يعود إلى الارتفاع مرة أخرى عندما ترتفع نسبة كبار السن نتيجة لهذا التحول .ينعكس انخفاض معدل الخصوبة ومعدل الوفيات مباشرة على نسبة الزيادة الطبيعية للسكان ، حيث تشير إسقاطات الأمم المتحدة ( الاحتمال المعدل ) إلى انخفاض هذه المعدلات بوتيرة أسرع في البلدان التي تقدمت فيها عملية التحول الديموغرافي ، ففي البلدان التي لا تزال في مرحلة أولية من انخفاض معدل الخصوبة ( كاليمن ) سيظل معدل الزيادة الطبيعية مستقراً خلال الفترة 2000 - 2020م ، ثم ينخفض ببطء ليصل إلى 2.2 % خلال الفترة 2020 - 2040م ، ويبقى أمامه مسافة طويلة لاستقرار الوضع الديموغرافي . وينخفض نمط هذا الانخفاض في البلدان التي تقدمت في مراحل انخفاض معدل الخصوبة ( كتونس ولبنان ) ، حيث ينخفض معدل الزيادة الطبيعية تدريجياً ليصل إلى صفر في نهاية النصف الأول من القرن الـ21 وهي حالة الاستقرار التام للوضع إلى أقل من 1 % خلال الفترة 2020 -2052م في معظم البلدان التي تقدمت فيها عملية التحول الديموغرافي ( كالإمارات العربية المتحدة والبحرين وتونس والجزائر وقطر والمغرب ) بينما تتجاوز 2 % في موريتانيا واليمن . ولعل من أهم نتائج التحول الديموغرافي ارتفاع نسبة السكان في سن العمل (15 - 59 سنة ) ونسبة المسنين ، وانخفاض نسبة الأطفال أقل من 15 سنة . وسيبقى لفئة الشباب حيز هام في جميع البلدان العربية ، وستشهد غالبيتها فترة رفاه من الناحية الديموغرافية ، حيث ستبقى نسبة السكان في سن العمل مرتفعة حتى عام 2020م أو ما بعده وفقاً لخصوصية كل بلد . وتعد النافذة الديموغرافية من المظاهر الايجابية في عملية التحول الديموغرافي ، إذ يمكن استثمارها في تحسين إنتاجية العمل ووضع برامج تعني بالتكافل بين الأجيال ، كما يمكن الاستفادة منها في تدعيم برامج التأمينات الاجتماعية ، لان عدد السكان الذين ينتمون إلى القوى العاملة في هذه المرحلة يفوق عدد السكان خارجها . ويمكن أن تسمح هذه الفترة من الرفاه الديموغرافي بخلق العديد من الفرص للاستثمار في المنطقة العربية ولاستغلال مواردها الطبيعية والبشرية على النحو الأمثل ، من حيث إتاحة التعليم والمعرفة بالتقنيات الحديثة ، المشاركة في النشاط الاقتصادي لكل الفئات .





سيناريوهات النمو السكاني في العالم

وضعت شعبة السكان في إدارة الأمم المتحدة للتنمية الاقتصادية والاجتماعية سيناريوهات مختلفة للحد من سكان العام في عام 2050م ، استنادا إلى مجموعة من الافتراضات بشأن معدلات الخصوبة وعوامل أخرى لها تأثيرها على النمو . ففي سيناريو المتغير المنخفض على سبيل المثال سيبلغ عدد سكان الكوكب 8 بلايين نسمة بحلول عام 2050م .ويفترض هذا السيناريو معدل خصوبة قدرة 54,1 ، الذي يقل كثيراً عن معدل خصوبة الإحلال البالغ 1,02 ويبلغ معدل الخصوبة الكلي في العالم حاليا 56,02 ووفقا لسيناريو المتغير المتوسط ، تتوقع شعبة السكان أن ينخفض معدل الخصوبة الكلي في المناطق الأقل نمو من 73, 2 طفل لكل أمراة في الفترة 2005- 2010م إلى 05, 2 في الفترة 2045- 2050م . وذكرت شعبة السكان أنه لكي يتحقق هذا الانخفاض من الضروري التوسع في فرص الحصول على خدمات تنظيم الأسرة الطوعي ، ولاسيما في أقل البلدان نموا وأبان عام 2005م ، بلغت نسبة استخدام وسائل منع الحمل الحديثة في أقل البلدان نموا 24% بين النساء في سن الإنجاب ، المتزوجات أو المقترنات بشريك . وكانت هناك نسبة 23% من بين هولاء النساء ممن لا يستخدمين وسائل منع الحمل ، على الرغم من عدم رغبتهن في الحمل الأن أو خلال العامين المقبلين تعريف الاحتياجات غير الملباة . ووفقا لما ذكره الأمين العام للأمم المتحدة في تقرير عن سكان العالم وبرنامج عمل المؤتمر الدولي للسكان والتنمية هناك قرابة 106 ملايين من النساء المتزوجات في البلدان النامية ممن تنقصهن أحدي الاحتياجات الملباة لغرض تنظيم الأسرة .
سيناريوهات سكان العالم 2050م
معدل منخفض معدل متوسط معدل مرتفع
959,7 150,9 461,10
معدل الخصوبة في العالم 2045-2050م حسب سيناريوهات النمو السكاني
معدل منخفض معدل متوسط معدل مرتفع
54, 1 02, 2 51, 2
وفق تقرير حالة سكان العالم 2009م (في مواجهة عالم متغير : المرأة والسكان والمناخ )
الظواهر الأخيرة لتغير المناخ تعزى الى النشاط البشري والحكومات والافراد مطالبون باتخاذ الإجراءات اللازمة لمنع وقوع الكارثة .عرض / بشير الحزمي ذكر تقرير حالة سكان العالم 2009م بان هناك كم متزايد من الدلائل التي تشير الى ان الظواهر الاخيرة لتغير المناخ انما تعزى في المقام الاول الى النشاط البشري ، وان تاثير تغير المناخ على الناس يتسم بالتعقيد فهو يحفز على الهجرة ويدمر سبل كسب الرزق ويعطل الاقتصاد ويقوض التنمية ويفاقم من أوجه عدم المساوة بين الرجال والنساء .وأشار التقرير الذي صدر هذا العام تحت عنوان (في مواجهة عالم متغير :المرأة والسكان والمناخ ) في ستة مكونات رئيسية وملحق خاص بالشباب الى ان تغير المناخ ينطوي على إمكانات من شأنها عكس مسار مكاسب التنمية التي جرى تحقيقها بشق الانفس على مدى العقود الماضية فضلاً على انة يهدد بتفاقم حدة الفقر وإثقال كاهل الجماعات المهمشة بمصاعب اضافية ، وان مستقبل تغير المناخ سوف يتوقف الى حد كبير على مدى سرعة تراكم غازات الدفيئة في الغلاف الجوي . وأوضح التقرير ان الفقراء لاسيما في البلدان النامية هم من سيواجهون اسواء الاثار الناجمة عن التغير المناخي . واستعراض التقرير الخطر الذي يشكله ذوبان الكتل الجليدية على إمدادات المياه اللازمة لزراعة الكفاف والمدن الضخمة ، بالإضافة إلى الآثار المحتملة للتغير المناخي على الصعيد الصحي والاجتماعي والبيئي والهجرة .وتطرق التقرير في أحد مكوناته الرئيسية الى عناصر تغير المناخ حيث أشار إلى ان ارتفاع درجة حرارة الغلاف الجوي للأرض يتسبب في أحوال مناخية قاسية ويؤدي الى ذوبان القمم الجليدية القطبية وحموضة المحيطات بمعدلات أسرع بكثير من ما توقع العلماء في الماضي .وفي المكون الثاني من التقرير (على حافة الخطر ) تمت الإشارة إلى ان تغير المناخ قد اصبح حقيقة واقعة وان التصدي لهذه المشكلة تتمثل في المقام الأول في العمل على وقف تدهور المشكلة حيث ان من شان الإجراءات التي تتخذ الان لتخفيض انبعاثات غازات الدفيئة في المستقبل ان تساعد الإنسانية على تفادي وقوع كارثة ونوه التقرير إلى وجود علاقة بين التغير السكاني والانبعاثات بيد ان اثر النمو السكاني على الانبعاثات يتضاعف بفعل عوامل اخرى ، وان العلاقة بين النمو السكاني وتزايد الانبعاثات ليست علاقة مباشرة . وذكر التقرير بان النساء تتحمل وطأة تغير المناخ وبين التقرير ان المرأة تتمتع بالقوة اللازمة لتعبئة الطاقات في مواجهة تغير المناخ غير ان هذه الطاقات لا يمكن إطلاقها الا من خلال السياسات التي من شأنها تمكين المرأة –حسب ما أوضحته السيدة ثريا أحمد عبيد المديرة التنفيذية لصندوق الأمم المتحدة للسكان في تصديرها للتقرير .وأشار التقرير في المكون الثالث منه (شد الرحال ) الى انه سيكون لتغير المناخ وأثاره السلبية على وسائل العيش والصحة العامة والامن الغذائي وإمدادات المياه وقعاً شديداً على التنقل البشري ، وأن من شان الكوارث المتعلقة بالتدهور البيئي وتغير المناخ ان تدفع بالناس الى هجر ديارهم .وفي مكونة الرابع ( بناء القدرة على التصدي ) طالب التقرير ملايين البشر أن يتكيفو مع الاثار الناجمة عن تغير المناخ . مستعرضاً اثار تغير المناخ والاهداف الانمائية للالفية . ودعا التقرير في مكونة الخامس ( التعبئة من أجل التغير ) الحكومات والإفراد على السواء ان يتخذوا الإجراءات اللازمة للإبطاء من وتيرة انبعاثات غازات الدفيئة ومنع وقوع كارثة .وحدد التقرير في مكونة السادس ( خمس خطوات للتراجع عن الهاوية )وهي تحقق تفهم أفضل للديناميات السكانية ، والنوع الاجتماعي والصحة الإنجابية إزاء تغير المناخ والناقشات البيئية الدائرة على جميع المستويات ، التمويل الكامل لخدمات تنظيم الأسرة وإمدادات وسائل منع الحمل في إطار الحقوق الإنجابية والصحية وضمان ان لا يكون انخفاض الدخل عائقاً امام الحصول على هذه الخدمات ، إعطاء الأولوية للبحوث وجمع البيانات من اجل تحسين تفهم دور الجنسين والديناميات السكانية في تخفيف تغير المناخ والتكيف معه ، وتحسين عمليات التصنيف حسب النوع الاجتماعي للبيانات المتصلة بتدفقات الهجرة الناجمة عن عوامل بيئية والاستعداد من الآن للزيادات في التحركات السكانية الناجمة عن تغير المناخ ، إدماج الاعتبارات المتعلقة بالنوع الاجتماعي في الجهود العالمية الرامية الى التخفيف من أثار تغير المناخ والتكيف معه .وفي ملحق الشباب الذي حمل عنوان ( في المواجهة :الشباب وتغير المناخ )تم استعراض الاثار المتوقعة لتغير المناخ بالنسبة لحياة الشباب وذلك من خلال الاستدلال بقصص لسبعة من الشباب والشابات من مختلف دول العالم والتي تضمنت لمحة عن تلك التاثيرات المحتملة .
تغير المناخ ، وبرنامج عمل المؤتمر الدولي للسكان والتنمية ، والأهداف الإنمائية للألفية
في برنامج عمل المؤتمر الدولي للسكان والتنمية لعام 1994م وردت الإشارة إلى "تغير المناخ" مرتين ، الأولي في ديباجة برنامج العمل باعتبار تغير المناخ مشكلة إيكولوجية تحركها إلى حد كبير الأنماط الإنتاجية والإستهلاكية التي لا يمكن لها أن تستمر والتي تضيف اخطاراً إلى الأخطار التي تهدد وفاة الاجيال المقبلة . وتدعو الوثيقة إلى زيارة التعاون الدولي في صدد السكان في سياق التنمية المستدامة لكنها لا تقدم تفاصيل محددة بشأن الكيفية التي يمكن بها توجيه واستخدام هذا التعاون أو تفاصيل محددة بشان دور السكان في تحقيق التنمية المستدامة وهناك إشارة إلى تغير المناخ حيث يشجع برنامج العمل الحكومات على النظر في طلبات الهجرة الواردة من البلدان التي يكون وجودها مهددا تهديدا وشيكا بسبب الاحترار العالمي وتغير المناخ .وقد تنامي الإهتمام العالمي بمسالة تغير المناخ في السنوات مابين المؤتمر الدولي للسكان والتنمية لعام 1994م ، وإعلان الأهداف الإنمائية للألفية عام 2000م . وقد ورد إنهاء تزايد إنبعاثات غازات الدفيئة بحلول عام 2015م باعتباره احد الغايات في إطار الهدف 7 من الأهداف الإنمائية للألفية ، الذي يرمي إلى ضمان الإستدامة البيئية . ويشير تقرير عن الأهداف الإنمائية للألفية ، صدر في عام 2008م ، إلى النمو السكاني إشارة عابرة ثلاث مرات ، لكنه لم يتطرق بالتفصيل إلى الديناميات السكانية أو علاقتها با لإستدامة البيئية أو الأهداف الأخرى . السكان والتكيفمن بين 41 برنامجا من برامج العمل الوطنية للتكيف والتي قدمتها حكومات البلدان النامية إلى أمانة إتفاقية الأمم المتحجة الإطارية المتعلقة بتغير المناخ قبل ايار / مايو 2009م هناك 37برنامجا تربط بشكل صريح بين تغير المناخ والسكان . وتحدد معدل النمو السكاني السريع بوصفة إحدي المشاكل التي من شأنها إما زيادة الأثار الناجمة عن تغير المناخ سوءا أو عرقلة قدرة البلدان على التكيف معه وفي إطار الإعداد لبرامج عمل التكيف الوطنية تحدد أقل البلدان نموا أولوياتها و إحتياجاتها في ما يتعلق بالتكيف مع تغير المناخ . ومن شأن النمو السكاني أن يسهم في ندرة المياه العذبة أو تدهور أراضي المحاصيل ، الأمر الذي قد يؤدي إلى تفاقم أثارة تغير المناخ . وكذلك فإن نمو السكان يمكن أن يعرقل قدرة الحكومات على تخفيف حدة الفقر وتحقيق الأهداف الإنمائية للألفية . مخاطر تغير المناخ يمكن أن يرتفع متوسط معدلات درجة الحراة عالميا بما يصل إلى 4,6 درجات مئوية بحلول نهاية هذا القرن .قد يتعرض ما تصل نسبته إلى 30% من الأنواع النباتية والحيوانية للانقراض إذا تجاوزت الزيادة في معدلات درجة الحرارة العالمية 5,2 درجة مئوية . قد يكون ثلث المرجانات البانية للشعاب في مختلف أنحاء العالم يهدد بالانقراض بسبب الإحترار و حموضة المياه .وقد يرتفع متوسط معدلات أسطح البحار عالميا بما مقداره 43 سنتيمترا بنهاية هذا القرن .قد يتلاشي جليد المنطقة القطبية الشمالية تماما خلال فصل الصيف بحلول النصف الثاني من هذا القرن .قد يواجه بلد واحد من كل ستة بلدان حالات نقص في الأغذية كل عام بسبب حالات الجفاف الشديدة .بحلول عام 2075م سيواجه مابين 3 بلايين و 7 بلايين من سكان العالم حالات نقص مزمنة في المياه .
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