retraining could come from a robot tax, although the idea is controversial. Compared to 1800s Only two nations today, globally have a population similar to the 19th century, or 1800s, Bulgaria and Ireland, both having seen emigration. Long-term future trends A long-term population decline is typically caused by sub-replacement fertility, coupled with a net immigration rate that fails to compensate for the excess of deaths over births. A long-term decline is accompanied by population aging and creates an increase in the ratio of retirees to workers and children. When a sub-replacement fertility rate remains constant, population decline accelerates over the long term. Because of the global decline in the fertility rate, projections of future global population show a marked slowing of population growth and the possibility of long-term decline. The table below summarizes the United Nations projections for future population growth. Any such long-term projections are necessarily highly speculative. The UN divides the world into six regions. Under their projections, during the period 2045–2050, Europe's population will be in decline and all other regions will experience significant reductions in growth; then, by the end of the 21st century (the period 2095–2100) three of these regions will be showing population decline and global population will have peaked and started to decline. Note: the UN's methods for generating these numbers are explained at this reference. The table shows that the UN predicts long-term decline of population growth rates in every region; however, short-term baby booms and healthcare improvements, among other factors, can cause reversals of trends. Population declines in the Russia Federation (1994–2008), Germany (1974–1984), and Ireland (1850–1961) have seen long-term reversals. The UK, having seen almost zero growth during the period 1975–1985, is now (2015–2020) growing at 0.6% per year. See also Biodiversity loss Birth dearth Societal collapse Negative Population Growth History of Easter Island#Destruction of society and population Human overpopulation Human population planning Political demography Population cycle Population growth Rural flight Sub-replacement fertility Zero population growth Church of Euthanasia Antinatalism Human extinction Case studies: Russian Cross Ageing of Europe Aging of the United States Aging of Japan List of sovereign states and dependencies by total fertility rate Empty diagonal References Further reading Aftermath of war Ageing Demographic economic problems