While future economic growth, social development and environmental conditions are difficult to predict, future demographic trends are considerably more certain, especially in the near term. Understanding and anticipating likely future demographic trends for the 21st century, 10 of which are highlighted below, can provide instructive insights to help guide sound policymaking, meaningful socio-economic development and environmental sustainability.
Larger world population: The world's population of 7.6 billion is growing at 1.1 percent annually, or approximately 83 million people. Although this rate is half the peak level of 2.1 percent in the late 1960s, the world's population has more than doubled since then and substantial demographic growth is expected in the coming decades.
World population, for example, is projected to reach 8 billion by 2023, 9 billion by 2037, 10 billion by 2055 and 11 billion by 2087. Even if the rate of growth were to decline more rapidly than currently expected, world population would reach nearly 9 billion by midcentury.
Population growth concentrated in developing regions: Nearly all of the world's annual population growth -- about 96 percent -- is taking place in developing countries. By far, the developing country contributing most to world population growth is India at 18 percent. The next five contributing countries are: China (6.7 percent), Nigeria (6 percent), Pakistan (4.6 percent), Indonesia (3.4 percent) and Democratic Republic of Congo (3.2 percent).
Among developed countries, the top contributing country to world population growth is the United States at 2.8 percent. After the US, and at considerably lower levels, the next five developed countries contributing to world population growth are: United Kingdom (0.5 percent), Canada (0.4 percent), Australia (0.4 percent), France (0.3 percent) and Germany (0.2 percent).
Population decline in many countries: As a result of sustained negative rates of demographic growth, the populations of nearly 40 countries are expected to be smaller by midcentury. If current birth rates were to remain unchanged, the populations, and in particular the size of the labor forces of many large economies -- including Germany, Italy, Japan, Russia and South Korea -- are projected to be substantially smaller by the end of the century.
In addition, many developed countries are dependent on international migration for their future population growth. For example, without future immigration, the populations of Australia, Canada, France, United Kingdom and United States would peak after several decades and then gradually become smaller and older than currently projected.
One out of every 20 people in the world today has yet to achieve life expectancy of 55 years at birth, the global average attained a half century ago.
More urbanization and larger cities: Most of the world's projected population growth over the coming decades will be in urban areas of developing countries. The majority of world population no longer consists of rural dwellers as has been the case throughout human history, but urban dwellers.
Over the next two decades, the population of urban areas in less-developed regions will double in size, growing from 1.9 billion to 3.9 billion. Also noteworthy is the emergence of mega-cities with populations of 10 million or more occurring largely in developing countries.
Many of these urban centers are located near coastlines. About a quarter-billion people worldwide are estimated to live along coastlines less than five meters above sea level. Climate change is making these urban centers more vulnerable to sea level rises, storm surges and flooding.
Lower mortality and higher life expectancies: Improved mortality rates and higher life expectancies are expected to continue through the 21st century. The current global life expectancy at birth of 71 years is projected to increase to 77 years by 2050, and 81 years well before the century's close. Some of the countries expected to have the highest life expectancy at birth of 88 years, by midcentury are Italy, Japan, Singapore, Spain and Switzerland.
The impact of diseases and epidemics, such as HIV/AIDS and Ebola, and low levels of socio-economic development has Africa's mortality lagging behind other regions. Despite impressive reductions in mortality, one out of every 20 people in the world -- have yet to achieve life expectancies at birth of 55 years, the global average attained a half century ago.
Lower fertility and more countries below replacement: By midcentury, every major region of the world except Africa will be at or below replacement level fertility of about 2.1 births per woman, which permits a population to replace itself from one generation to the next. Today, more than 80 countries, accounting for close to half of the world's population, have fertility at or below the replacement level, including China, the United States, Brazil, Russia, Japan, Vietnam, Germany, Iran, Thailand and the United Kingdom (ranked by size).
In many of those countries, including Canada, Germany, Hungary, Japan, Italy, South Korea, Spain and the United Kingdom, fertility levels have remained below replacement for several decades. As a result, governments are concerned about population decline and aging and the social, economic and cultural consequences of very low fertility, with many adopting a variety of policy measures to encourage higher birth rates.
However, government attempts to raise fertility to replacement levels have generally not achieved their desired goals. The financial, social and personal costs of raising additional children are simply too high and onerous, especially for women.
Population aging and increased longevity: As a result of low fertility and increased longevity, population aging will be even more critical during the 21st century. In many countries, including Germany, Italy, Japan and Spain, the potential support ratio, which is the ratio of the working age population aged 15 to 64 years per one person 65 years or older, is projected to decline to less than two people in the working ages per one elderly person.
Also by midcentury, the proportion of world population aged 65 years or older is expected to double, i.e. from 7 percent to 16 percent. In many countries, such as China, Germany, Italy, Japan, South Korea and Spain, one person out of three is expected to be 65 years or over by 2065.
Due to the increasing elderly population coupled with the relative decline of workers paying taxes, many countries are confronting difficult choices concerning budgetary allocations, taxation levels and provision of social services. To avoid controversial budgetary reforms and unpopular tax increases, some governments are reducing expenditures and entitlements for the elderly and shifting more of the costs for support, care giving and health services to the old and their families.
Progress in women's equality: The progress achieved in women's equality during the 20th century is expected to continue during the 21st century. Worldwide women now outnumber men in both university attendance and graduation. Growing numbers of women are seeking higher education, employment, political office and social identity.
Although women's educational attainment exceeds that of men in most countries, women remain behind men in such realms as income, business ownership, research and politics. Different fields of study and vocational training chosen by women and men may explain some disparities. However, the persistence of the female disadvantage suggests that societal expectations and cultural norms on the appropriate roles for women and men are limiting the achievement of gender equality.
Changing family composition and household structure: The concept of the family household has been generally equated with the nuclear family, i.e., father, mother and children. Recently, definitions of the family have proliferated to reflect differing lifestyles and circumstances. The family consisting of "a working father, stay-at-home mom, some children and marriage "until death do us part" increasingly appears no longer to be the societal norm in many countries. In many countries, being married has become less of a necessity for financial survival, social interaction and personal wellbeing.
Single-parent households have also increased markedly during the past several decades. In some regions such as Latin America, the proportions of births outside marriage are estimated at more than 60 percent. Also, in many European countries, the majority of births occur outside marriage, with government assistance typically provided to single parents. Today, about 14 percent of the world's 2.3 billion children reside in a single-parent household, most often with a mother.
A related global transformation in living arrangements with wide-ranging consequences is the rise of one-person households. Of the world's 2 billion households, about 15 percent -- or 300 million -- are one-person households.
The proportion of people who live alone has grown steadily over the recent past. Since the 1960s, for example, one-person households in many countries have increased substantially. In many European countries, as well as in Australia, Canada, China, Japan, South Korea and the United States, the proportion of one-person households has more than doubled.
One-person households offer opportunities for men and women wishing to have privacy, solitude, introspection and personal lifestyle choices. However, growing numbers of one-person households also pose challenges to the social and economic development of urban centers and rural areas and the capacities of governments to provide assistance, services and care to those living alone, particularly the elderly.
Increased international migration: Approximately 250 million people, or slightly more than 3 percent of world population, are international migrants. While the total number of emigrants has more than tripled during the past half century, the proportion of emigrants has remained between 2 to 3 percent of world population.
The country hosting the largest numbers of immigrants is the United States, with nearly 47 million or about one-fifth of the world total. In second and third places are Germany and Russia, each hosting about 12 million immigrants. In contrast, most immigrants are from developing countries, with India accounting for the largest number of emigrants, approximately 16 million, followed by Mexico (12 million) and China (10 million).
Internationally, migrants are estimated to be sending about US $600 billion to their families in their home countries, with developing countries receiving close to 75 percent of all remittances. The US was the largest remittance source country, with an estimated $56 billion in outward flows in 2014, followed by Saudi Arabia ($37 billion) and Russia ($33 billion). India was the largest remittance receiving country, with an estimated $72 billion in 2015, followed by China ($64 billion) and the Philippines ($30 billion).
Over the next 50 years, developed regions are expected to continue being net receivers of international migrants, with an average gain of at least several million per year. In addition to playing an increasingly important demographic role, the increased presence and flows of migrants is expected to have significant social, economic, cultural and political consequences throughout the 21st century.
Future international migration flows will also continue to include the exodus of humanity's desperate, which is taking place despite walls, fences, barriers, guards, patrol ships, warnings and nativist political rhetoric. Governments of origin, transit and destination countries are continuing to struggle on how best to cope unauthorized migration flows. Although governments have a wide range of possible responses to illegal migration, they are likely to continue avoiding needed actions due to limited resources, human rights concerns, divided public opinion and political concerns.
The revolutionary demographic changes that the world continues to experience are impacting virtually every aspect of human life, including the environment. However, as is often the case when confronting slow-moving, yet momentous demographic trends, policy makers tend to defer addressing the consequences to others in the distant future. However, postponing decisions -- especially regarding budgetary allocations, taxation, pensions and health services -- increase the difficulties and costs of implementing needed policies and programs as well as adversely impacting human welfare.
Understanding the profound demographic changes now underway and anticipating their juggernaut consequences provide valuable insight for governmental policymaking, economic decisions and development efforts. Such insight can contribute substantially to the setting of meaningful goals, designing effective social, economic and environmental strategies, evaluating program outcomes and achieving genuine progress. On the other hand, ignoring or dismissing those major demographic trends will likely result in imprudent policies, wasted resources, inadequate programs and declines in the overall wellbeing of the world's population.