why has been there a general decline throughout the world? How has this affected the world population?
Answer in about 40 to 50 words.
Answers
What we might talk about as population size is actually population density, the number of individuals per unit area (or unit volume). Population growth is based on four fundamental factors: birth rate, death rate, immigration, and emigration.
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Answer:
The conventional projection by the UN is that world population, currently 7.7 billion, will increase to 11.2 billion in 2100, then stabilise before slowly declining. However, current trends cast much doubt on this picture. Fertility rates are in dramatic decline worldwide and world population may peak below nine billion by 2050 and then decline.
In order for a human population to maintain its numbers, each woman must bear, on average, 2.1 children. If the birth rate exceeds 2.1, population numbers increase; if it is less than 2.1, population numbers decline. Birth rates below 2.1 have been common now since 1970. Ireland had a birth rate of 1.92 in 2016 but inward migration is contributing to population growth.
The UN World Fertility Patterns 2015 Report details birth rates (children per woman) for the major world regions – Africa 4.7, Asia 2.2, Europe 1.6, Latin America/Caribbean 2.2, North America 1.9, Oceania 2.4. The overall world fertility rate is 2.5. So world population numbers continue to grow.
World population trends were reviewed recently by Darrell Bricker and John Ibbitson in the Observer on January 27th. The authors seriously questioned the UN projection that world population numbers would continue to increase until 2100, quoting several well-respected demographers. Jorgen Randers, a Norwegian academic who decades ago warned of a potential global catastrophe caused by overpopulation, has changed his mind.