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According to current projections of population growth, the world population of humans will continue to grow until at least 2050, with the estimated population, based on current growth trends, to reach 9 billion in 2040,〔(【引用サイトリンク】title=World Population Clock )〕〔(International Data Base (IDB) — World Population )〕 and some predictions putting the population in 2050 as high as 11 billion.〔http://esa.un.org/unpp/〕 World population passed the 7 billion mark on October 31, 2011.〔 According to the United Nations' World Population Prospects report,〔(World Population Prospects )〕 the world population is currently growing by approximately 74 million people per year. Current United Nations predictions estimate that the world population will reach 9.0 billion around 2050, assuming a decrease in average fertility rate from 2.5 down to 2.0.〔(United Nations Population Division Home Page ), United Nations Department of Economic and Social Affairs〕〔(Microsoft Word – WorldPOP2300.doc )〕 Almost all growth will take place in the less developed regions, where today's 98.3 million population of underdeveloped countries is expected to increase to 7.8 billion in 2050. By contrast, the population of the more developed regions will remain mostly unchanged, at 1.2 billion. An exception is the United States population, which is expected to increase 31% from 305 million in 2008 to 400 million in 2050 due to projected net international migration.〔()〕 In 2000–2005, the average world fertility was 2.65 children per woman, about half the level in 1950–1955 (5 children per woman). In the medium variant, global fertility is projected to decline further to 2.05 children per woman. == Growth regions == During 2005–2050, twelve countries are expected to account for half of the world's projected population increase: India, China, United States, Indonesia, Nigeria, Pakistan, Brazil, Democratic Republic of the Congo, Ethiopia, Philippines, Mexico and Egypt, listed according to the size of their contribution to population growth. Global life expectancy at birth, which is estimated to have risen from 46 years in 1950–1955 to 65 years in 2000–2005, is expected to keep rising to reach 75 years in 2045–2050. In the more developed regions, the projected increase is from 75 years today to 82 years by mid-century. Among the least developed countries, where life expectancy today is just under 50 years, it is expected to be 66 years in 2045–2050. The population of 31 countries or areas, including Ukraine, Romania, Japan and most of the successor States of the former Soviet Union, is expected to be lower in 2050 than in 2005. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Projections of population growth」の詳細全文を読む スポンサード リンク
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