２１００年の世界人口、８８億人に　国連予測から２１億人減

【パリＡＦＰ＝時事】2100年の世界人口は88億人となり、現時点で国連が算出した予測よりも21億人少なくなるとする論文が、14日に英医学誌ランセットに掲載された。出生率の低下と人口の高齢化により、世界の勢力図が一新されると予測している。（写真は資料写真）
　論文を発表した国際的な研究チームによると、２１世紀の終わりまでに１９５か国中１８３か国で、移民の流入が無い場合に、人口維持に必要な数値を下回るという。
　日本、スペイン、イタリア、タイ、ポルトガル、韓国、ポーランドを含む２０か国以上では２１００年までに人口が半分以上減少し、中国の人口も今後８０年間で現在の１４億人から７億３０００万人に減ると予想された。
　一方でサハラ砂漠以南のアフリカの人口は、現在の３倍の約３０億人に増加する。２１００年にはナイジェリアの人口は約８億人に増え、インドの１１億人に次いで２位となる。

■新たな多極化世界
　出生率の低下と高齢化により労働年齢人口が激減することは、多くの国にとって大きな課題となる。例えば、中国の国内総生産（ＧＤＰ）は２０５０年までに米国を抜いて世界１位となるが、２１００年までには２位に戻ると予測される。
　インドのＧＤＰは３位に上昇し、経済規模では日本、ドイツ、フランス、英国が上位１０か国にとどまる。インドネシアが１２位につけ、ナイジェリアは現在の２８位から１０位以内に入るとされる。
　ランセット誌のリチャード・ホートン編集長は、「２１世紀の終わりまでには世界は多極的になり、インド、ナイジェリア、中国、米国が覇権を握る」とし、今回の論文は「地政学的な勢力の抜本的な変化」のあらましを述べているとコメントした。
　これまで世界人口の予測に関しては、国連が事実上独占的な地位を築いていた。国連は世界の人口について、２０３０年に８５億人、２０５０年に９７億人、２１００年に１０９億人になると予測している。
　ランセット誌に掲載された論文との違いは、出生率に関する見通しにある。国連は、現在出生率が低い国で、時間とともに合計特殊出生率は約１．８に増加すると予測している。
　一方で論文執筆者は、「女性がもっと教育を受け、出産関連の公共医療サービスを受けるようになると、女性１人当たりが産む子どもの数は１．５人未満になると分析している」と説明した。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/07/16-11:51）

Earth will be home to 8.8 billion souls in 2100, two billion fewer than current UN projections, according to a major study published Wednesday that foresees new global power alignments shaped by declining fertility rates and greying populations.
By century's end, 183 of 195 countries -- barring an influx of immigrants -- will have fallen below the replacement threshold needed to maintain population levels, an international team of researchers reported in The Lancet.
More than 20 countries -- including Japan, Spain, Italy, Thailand, Portugal, South Korea and Poland -- will see their numbers diminish by at least half.
China's will fall nearly that much, from 1.4 billion people today to 730 million in 80 years.
Sub-Saharan Africa, meanwhile, will triple in size to some three billion people, with Nigeria alone expanding to almost 800 million in 2100, second only to India's 1.1 billion.
These forecasts suggest good news for the environment, with less stress on food production systems and lower carbon emissions, as well as significant economic opportunity for parts of sub-Saharan Africa, lead author Christopher Murray, director of the Institute for Health Metrics and Evaluation (IHME) at the University of Washington, told AFP.
However, most countries outside of Africa will see shrinking workforces and inverting population pyramids, which will have profound negative consequences for the economy.
For high-income countries in this category, the best solutions for sustaining population levels and economic growth will be flexible immigration policies and social support for families who want children, the study concluded.
However, in the face of declining population there is a very real danger that some countries might consider policies that restrict access to reproductive health services, with potentially devastating consequences, Murray cautioned.
- 866 million people over 80 -
It is imperative that women's freedom and rights are at the top of every government's development agenda.
Social services and healthcare systems will need to be overhauled to accommodate much older populations.
As fertility falls and life expectancy increases worldwide, the number of children under five is forecast to decline by more than 40 percent, from 681 million in 2017 to 401 million in 2100, the study found.
At the other end of the spectrum, 2.37 billion people -- more than a quarter of the global population -- will be over 65 years old by then.
Those over 80 will balloon from about 140 million today to 866 million.
Sharp declines in the number and proportion of the working-age population will also pose huge challenges in many countries.
Societies will struggle to grow with fewer workers and taxpayers, noted Stein Emil Vollset, a professor at the IHME.
The number of people of working age in China, for example, will plummet from about 950 million today to just over 350 million by the end of the century -- a 62 percent drop.
The decline in India is projected to be less steep, from 762 to 578 million.
In Nigeria, by contrast, the active labour force will expand from 86 million today to more than 450 million in 2100.
These tectonic shifts will also reshuffle the pecking order in terms of economic clout, the researchers forecast.
- A new multipolar world -
By 2050, China's gross domestic product will overtake that of the United States, but fall back into second place by 2100, they predict.
India's GDP will rise to take the number three spot, while Japan, Germany, France and the UK will stay among the world's 10 largest economies.
Brazil is projected to fall in ranking from eighth today to 13th, and Russia from the number 10 spot to 14th. Historical powers Italy and Spain, meanwhile, decline from the top 15 to 25th and 28th, respectively.
Indonesia could become the 12th largest economy globally, while Nigeria -- currently 28th -- is projected to crack the top 10.
By the end of the century, the world will be multipolar, with India, Nigeria, China and the United States the dominant powers, said Richard Horton, describing the study as outlining radical shifts in geopolitical power.
Until now, the United Nations -- which forecasts 8.5, 9.7 and 10.9 billion people in 2030, 2050 and 2100, respectively -- has virtually had a monopoly in projecting global population.
The difference between the UN and IHME figures hinges crucially on fertility rates. The so-called replacement rate for a stable population is 2.1 births per woman.
UN calculations assume that countries with low fertility today will see those rates increase, on average, to about 1.8 children per woman over time, said Murray.
Our analysis suggests that as women become more educated and have access to reproductive health services, they choose to have less than 1.5 children on average, he explained by email.
Continued global population growth through the century is no longer the most likely trajectory for the world's population.
Founded in 2007 and supported by the Bill and & Melinda Gates Foundation, the IHME had become a global reference for health statistics, especially its annual Global Burden of Disease reports.