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.
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.
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, caregiving and health services to the old and their families.
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. 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).