Landmark report predicts “profound” shifts in fertility by 2100

At the present moment, it can be near impossible to imagine life after Covid-19 — to look beyond next week, month, or year. However, in a sweeping new report published Tuesday in The Lancet, researchers offer a glimpse of our future world 80 years down the line.

According to the findings, the world is primed to undergo a massive overhaul in the way we move, reproduce, and work due to widespread declining fertility rates.

The global total fertility rate (TFR) — a metric that captures the average number of children a woman has over her lifetime — is predicted to steadily decline. In 2017, the TFR was 2.37. In 2100, it's expected to be 1.66. The United States' TFR specifically is predicted to move from 1.8 to 1.5 within that same time frame.

But it's not all doom and gloom: While a global trend of declining population numbers may seem worrying, the projections may actually enable communities to adapt more quickly to climate change, lessen stress on food supplies, and mitigate planetary destruction, the report suggests. With dwindling human capital, organizations will need to think creatively to fuel future economic growth.

Stein Emil Vollset, study co-author and researcher at the Institute for Health Metrics and Evaluation. He tells Inverse that the "implications of this study on people's lives and livelihood are profound."

"This study examines the future of societal, economic, and geopolitical power and offers world leaders important information from which to plan their nations’ futures," Vollset says.

Countries or communities are expected to experience changes across a gradient — with China and the United States losing more working-age people and Africa and the Middle East experiencing population booms.

Richard Horton, a physician and the editor-in-chief of The Lancet, commented that the new report documents a new chapter of human history.

"By the end of the century, the world will be multipolar, with India, Nigeria, China, and the US the dominant powers," Horton says. "This will truly be a new world, one we should be preparing for today."

To model this future world, a team of researchers mapped out global, regional, and national population scenarios based on fertility, migration, and mortality rates for 195 countries and territories from 2017 to 2100. They harnessed data from the Global Burden of Disease Study to project future global, regional, and national populations.

Based on their analysis:

• The world's population will peak in 2064 at 9.73 billion then drop off, shrinking to 8.79 billion by 2100.
• The team estimates that by 2100, 183 of 195 countries around the world will have total fertility rates below 2.1 births per woman. This is the birth rate that researchers consider necessary to maintain existing population levels long-term without immigration.
• Twenty-three countries may see populations shrink by more than half, including Japan, Thailand, Italy, and Spain.
• Globally, the team predicts an estimated 2.37 billion individuals over age 65 in 2100, compared with 1.7 billion under 20 years old.
• In some places like India and China, the number of working-age people is predicted to plummet more than others, creating a pressing shortage of human capital.
• While China is set to replace the USA in 2035 with the largest total gross domestic product (GDP) globally, rapid population decline from 2050 onward will disrupt this economic growth. As a result, the USA is expected to reclaim the top spot by 2098, if immigration continues to sustain the US workforce.

Fewer people on the planet, Vollset explains, isn't necessarily a bad thing. A population decline means there is likely to be less over-crowding in large urban areas, less pressure on systems to provide sustainable sources of food, and less stress on the environment.

But he also forecasts economic challenges, "as societies struggle to grow with fewer workers and taxpayers, and countries' abilities to generate the wealth needed to fund social support and health care for the elderly are reduced."

Why is fertility declining?

The landmark report was written before the Covid-19 pandemic began, Vollset says. It's not the disease outbreak reshaping human civilization. Instead, it's the rate at which people are having children.

"Fertility is the key driver in changes to population size," he explains. "The excess deaths caused by the pandemic are unlikely to significantly alter longer-term forecasting trends of global population."

The global fertility decline does stem from expanding access to contraception and education for women —reproductive rights which the authors fear may be under threat if governments reactively institute restrictive policies due to population declines.

"The excess deaths caused by the pandemic are unlikely to significantly alter longer-term forecasting trends of global population."

Christopher Murray, the study's lead author and the director of Institute for Health Metrics and Evaluation, explains that for high-income countries with below-replacement fertility rates, the best solutions for sustaining current population levels, economic growth, and geopolitical security are open immigration policies and social policies supportive of families having their desired number of children.

"However, a very real danger exists that, in the face of declining population, some countries might consider policies that restrict access to reproductive health services, with potentially devastating consequences," Murray said. "It is imperative that women's freedom and rights are at the top of every government's development agenda."

Volset echoes Murray's argument for reproductive rights.

"Our findings suggest that the decline in the numbers of working-age adults alone will reduce GDP growth rates that could result in major shifts in global economic power by the century's end," Vollset says. "Responding to population decline is likely to become an overriding policy concern in many nations, but must not compromise efforts to enhance women's reproductive health or progress on women's rights."

Abstract:

Background: Understanding potential patterns in future population levels is crucial for anticipating and planning for changing age structures, resource and health-care needs, and environmental and economic landscapes. Future fertility patterns are a key input to estimation of future population size, but they are surrounded by substantial uncertainty and diverging methodologies of estimation and forecasting, leading to important di!erences in global population projections. Changing population size and age structure might have profound economic, social, and geopolitical impacts in many countries. In this study, we developed novel methods for forecasting mortality, fertility, migration, and population. We also assessed potential economic and geopolitical e!ects of future demographic shifts.

Methods: We modelled future population in reference and alternative scenarios as a function of fertility, migration, and mortality rates. We developed statistical models for completed cohort fertility at age 50 years (CCF50). Completed cohort fertility is much more stable over time than the period measure of the total fertility rate (TFR). We modelled CCF50 as a time-series random walk function of educational attainment and contraceptive met need. Age-specific fertility rates were modelled as a function of CCF50 and covariates. We modelled age-specific mortality to 2100 using underlying mortality, a risk factor scalar, and an autoregressive integrated moving average (ARIMA) model. Net migration was modelled as a function of the Socio-demographic Index, crude population growth rate, and deaths from war and natural disasters; and use of an ARIMA model. The model framework was used to develop a reference scenario and alternative scenarios based on the pace of change in educational attainment and contraceptive met need. We estimated the size of gross domestic product for each country and territory in the reference scenario. Forecast uncertainty intervals (UIs) incorporated uncertainty propagated from past data inputs, model estimation, and forecast data distributions.

Findings: The global TFR in the reference scenario was forecasted to be 1·66 (95% UI 1·33–2·08) in 2100. In the reference scenario, the global population was projected to peak in 2064 at 9·73 billion (8·84–10·9) people and decline to 8·79 billion (6·83–11·8) in 2100. The reference projections for the five largest countries in 2100 were India (1·09 billion [0·72–1·71], Nigeria (791 million [594–1056]), China (732 million [456–1499]), the USA (336 million [248–456]), and Pakistan (248 million [151–427]). Findings also suggest a shifting age structure in many parts of the world, with 2·37 billion (1·91–2·87) individuals older than 65 years and 1·70 billion (1·11–2·81) individuals younger than 20 years, forecasted globally in 2100. By 2050, 151 countries were forecasted to have a TFR lower than the replacement level (TFR <2·1), and 183 were forecasted to have a TFR lower than replacement by 2100. 23 countries in the reference scenario, including Japan, Thailand, and Spain, were forecasted to have population declines greater than 50% from 2017 to 2100; China’s population was forecasted to decline by 48·0% (–6·1 to 68·4). China was forecasted to become the largest economy by 2035 but in the reference scenario, the USA was forecasted to once again become the largest economy in 2098. Our alternative scenarios suggest that meeting the Sustainable Development Goals targets for education and contraceptive met need would result in a global population of 6·29 billion (4·82–8·73) in 2100 and a population of 6·88 billion (5·27–9·51) when assuming 99th percentile rates of change in these drivers.

Interpretation: Our findings suggest that continued trends in female educational attainment and access to contraception will hasten declines in fertility and slow population growth. A sustained TFR lower than the replacement level in many countries, including China and India, would have economic, social, environmental, and geopolitical consequences. Policy options to adapt to continued low fertility, while sustaining and enhancing female reproductive health, will be crucial in the years to come.