世界人口達到 80 億——這是研究人員預測的增長方式
聯合國模型預測人口增長率低於之前的估計。
資料來源：大衛·亞當/新聞/2022 年 11 月 15 日/自然/財團法人台灣紅絲帶基金會編譯
據聯合國估計，世界人口在 11 月 15 日達到 80 億。
圖片來源：Jean-Marc Zaorski/Gamma-Rapho/Getty
根據聯合國的模型，今天世界人口將達到 80 億——距離超過 70 億僅過去了 12 年，距離地球僅供養 20 億人口不到一個世紀。
今年 7 月發布的最新聯合國人口更新也將其長期預測從 110 億下調至 2100 年的 104 億。
資料來源：聯合國人口司資料來源：聯合國人口司
人口學家永遠無法確定 11 月 15 日是否真的是聯合國命名的「八十億日」，但他們確實同意一件事。 儘管人口增長迅速，但這種增長正在放緩——而且，在幾十年內，地球人口將開始減少。
「這是一個粗略的近似值，更像是一個像徵性的發現」，紐約市聯合國人口司人口工作負責人帕特里克·格蘭德說。「我們可能已經過了，也可能會晚一點，但大約在這個時候，人類將達到 80 億」。
全球人口將增長多遠？ 研究人員不能同意
雖然是近似值，但這可能是聯合國迄今為止做出的最可靠的估計。 該組織最近改變了它分析數據的方式，從每五年一次改為每年一次。 近幾十年來，許多國家收集統計數據的能力一直在穩步提高。
然而，仍然存在重大不確定性，特別是對於正在經歷人道主義危機和衝突的國家，例如索馬利亞、葉門和敘利亞。「世界各地的基礎經驗信息的準確性差異很大」，Gerland 說。
不同的估計
整個二十世紀人口的快速增長（見「世界人民」）是由公共衛生和醫學的進步推動的，這使得更多的兒童能夠活到成年。 與此同時，低收入國家的生育率（定義為每位婦女生育的平均子女數）居高不下。
人口學家對生育率及其預期變化方式特別感興趣，因為這些因素有助於推動未來全球人口的變化。 例如，假設生育率的差異是各種模型先前對 2100 年世界人口的預測出現明顯偏差的一個重要原因。 這些結果顯示，到本世紀末，擴散範圍從 88 億到近 110 億。
中國人口何時見頂？ 這取決於你問誰
「即使你對這些生育率軌跡進行相對較小的調整，它也會累積起來，突然之間，一個大國在 80 年後可能會增加 1 億人口」，維也納人口研究所人口研究員 Tomáš Sobotka 說。
2018 年，位於維也納的國際應用系統分析研究所 (IIASA) 預測，2100 年全球人口將達到 95 億左右。該研究所目前正在準備更新，將這一估計提高到 100 億至 101 億之間。 Sobotka 說，這種變化是由於低收入國家兒童的觀察到和預期存活率更高。 另一個因素是一些大國（包括巴基斯坦）的生育率估計值較高。
數據更可靠
聯合國更新預測背後最重要的因素是，自中國 2015 年結束一胎化政策以來，來自中國的數據更加可靠。
「在該政策實施期間，來自中國的不同數據來源總是不匹配」，Gerland 說。 他說，一些父母，特別是如果他們有一個女孩，不會登記最初的出生。 因此，許多兒童在開始上學後才出現在官方統計數據中。「我們基本上不得不依靠教育統計數據來獲得更準確的信息」，他說。
聯合國的預測表明，中國人口已經達到頂峰，現在至少到本世紀末將逐年減少。
「中國的統計數據顯示，中國的死亡人數已經超過出生人數，在這種情況下，人口將開始下降」，格蘭德說。
doi: https://doi.org/10.1038/d41586-022-03720-6
World population hits eight billion — here’s how researchers predict it will grow
United Nations model predicts a slower rate of population growth than was previously estimated.
David Adam/NEWS/15 November 2022/Nature
The world’s population hit eight billion on 15 November, according to United Nations estimates.Credit: Jean-Marc Zaorski/Gamma-Rapho/Getty
According to the models of the United Nations, the world’s population will reach 8 billion today — a mere 12 years since it passed 7 billion, and less than a century after the planet supported just 2 billion people.
The latest UN population update, released in July this year, also revises its long-term projection down from 11 billion people to 10.4 billion by 2100.
Source: UN Population DivisionSource: UN Population Division
Demographers will never be sure whether 15 November really was the Day of Eight Billion, as the UN has named it, but they do agree on one thing. Although the human population has grown rapidly, that growth is slowing — and, within a few decades, Earth’s population will begin to shrink.
“It is a crude approximation that is more of a symbolic finding,” says Patrick Gerland, who leads demographic work at the UN Population Division in New York City. “We may have passed it, or it may be a little later, but it’s around this time that humanity is reaching eight billion.”
How far will global population rise? Researchers can’t agree
Although approximate, this could be the most reliable estimate that the UN has produced so far. The organization recently changed how it analyses data, switching from five-yearly to annual intervals. And there has been a steady improvement in recent decades in the ability and capacity of many countries to collect statistics.
Significant uncertainties remain, however, particularly for countries that are experiencing humanitarian crises and conflicts, such as Somalia, Yemen and Syria. “The accuracy of the underlying, empirical information varies tremendously around the world,” Gerland says.
Differing estimates
The rapid rise in population throughout the twentieth century (see ‘People of the world’) was driven by advances in public health and medicine, which allowed more children to survive to adulthood. At the same time, fertility rates (defined as the average number of children per woman) stayed high in lower-income countries.
Demographers take a particular interest in fertility rates and how they are expected to change, because these factors help to drive what will happen to the global population in the future. Differences in assumed fertility rates have been an important reason behind a notable diversion in what various models had previously forecast for the world’s population in 2100, for example. Those results suggested a spread ranging from 8.8 billion to nearly 11 billion by the end of the century.
When will China’s population peak? It depends who you ask
“If you make even relatively small adjustments in these fertility-rate trajectories, it accumulates, and suddenly a big country can have 100 million people more 80 years from now,” says Tomáš Sobotka, a population researcher at the Vienna Institute of Demography.
In 2018, the International Institute for Applied Systems Analysis (IIASA) in Vienna forecast that the global population would be about 9.5 billion in 2100. The institute is now preparing an update, which will raise that estimate to between 10 billion and 10.1 billion. The change is due to higher observed and expected survival rates among children in lower-income countries, Sobotka says. Another factor is higher estimates of fertility rates in some large countries, including Pakistan.
More reliable data
The most significant factor behind the UN’s updated forecast is that data from China have been more reliable since the end of the country’s one-child policy in 2015.
“There was always a mismatch in the different sources of data coming from China during that policy,” Gerland says. Some parents, particularly if they had a girl, would not register an initial birth, he says. For that reason, many children did not appear in official statistics until they started to attend school. “We basically had to rely on education statistics for more accurate information,” he says.
The UN predictions suggest that China’s population has already peaked and will now shrink year-on-year until at least the end of the century.
“The Chinese statistics are suggesting there are already more deaths than births in China, and in that situation, the population will start to decline,” Gerland says.
doi: https://doi.org/10.1038/d41586-022-03720-6