Introduction 

Changes in the human population have fluctuated throughout history. Since 1987, the population has risen by one billion every twelve years, leaving our current global population close to 8 billion! Population change has profound effects on the climate, spread of disease, economics, and military power. Extreme changes in population that drastically change society are an often overlooked existential threat.

History of Population

Until around 1800, the world population remained stable due to a high birth and death rate. With the Industrial Revolution came advancements in technology. While the birth rate remained unchanged, advances in public health reduced the mortality rate, specifically in infants and children, bringing a drastic spike in population from one billion in 1804 to two billion by 1927. By 1960, the population grew another billion due to the post-World War II birth spike. This generation, known as baby boomers, contributed significantly to the economy (Barnier). Approximately 60 years later, lifespans have doubled, and the human population has increased by five billion. 

Economists and philosophers have long debated the effects of population on our global society and how population increases can adversely affect communities. English economist and demographer Thomas Malthus (1766-1834) theorized that high rates of population growth would eventually surpass food supply and that human improvement is only possible with limits on reproduction (MacRae). He believed high fertility leads to poor economic performance. On the other hand, Karl Marx (1818-1883), a German philosopher and economist, believed that poverty causes high fertility. With poverty, educational opportunities are not easily accessible, especially for women, leading to limited skilled experts and lower production, lower government revenue, and economy, leading to higher fertility (McLellan).

Historically, deadly pandemics and their significant economic downturns periodically coupled with world population growth. In the 1340s, one to two-thirds of Europe's population died from bubonic plague, making it the deadliest pandemic to strike the world (Howard). In the 19th and 20th centuries, during the height of the Industrial Revolution, cholera contaminated water, spreading disease and killing hundreds of thousands of people in multiple outbreaks ("Cholera"). The Spanish Flu took 500 million lives. Even today, the world is still combating the current global pandemic, COVID-19. After more than two years of COVID-19, a significant disruption in the global supply chains, labor shortages, and increased wages across different industries make it harder for countries to revive their economies. 

Underpopulation 

With the many fatalities of each pandemic, birth rates dip in many countries, threatening their national sovereignty and the very existence of these nations. Underpopulation is "a situation in which there are too few people to realize the economic potential of an area or support its population's standard of living." ("Underpopulation"). Two underlying causes of a shrinking population include high rates of emigration and declining birth rates (VanDyke). One of the most prominent examples of population decrease was in Latvia, which lost 17% of its population since joining the EU and recorded twice as many deaths as births in the first half of 2021. Latvia is experiencing high emigration rates from economic and sociopolitical changes (VanDyke). Many regions of the country experience low average salaries and high unemployment rates, leaving Latvia with a "..shrinking labor force, an aging population, and stagnant economic growth." Moreover, the country's resistance to immigration from outside the EU further reduces the ratio of the economically active population and the dependent population, driving the country farther from achieving a "demographic bonus" that would lead to an increased economic output (Lovett).

Among well-developed countries, a population decline of 16.3% will occur in Japan in the next 30 years due to higher education levels for women, which have led to changes in cultural norms, including changes in marriage patterns. (VanDyke). Modernization and cultural shifts empower women, wherein having children becomes a question of economics and opportunity cost (Dhanesha). Similarly, the U.S. population showed a downward trend of 0.62 percent in 2017-2018, marking the nation's lowest growth in 80 years. This current dip in the national population growth resulted from young adult millennials postponing births after the Great Recession of 2007-2009. "..as it [the population] dropped from 1.6 million in 2000-2001, to just above 1 million in 2017-2018. There were fewer births than in recent decades and more deaths than in earlier years." (Frey). As the number of women of childbearing age declines and the baby boomers age, immigration has become an essential factor in population growth. While the U.S.'s growth rate is still much higher than Japan's and Latvia's, loosening restrictions on immigration policies can aid the economy's future growth and provide care for the increasing aging population.

Low birth rates in China result from strict population restrictions created in 1980. The one-child policy was established in China to curb the population and promote economic growth. With the policy came the ramification of a smaller, young economically-active population relative to a much larger dependent and aging population. The country is facing falling birth rates, even after the policy changed to two children per family in 2016 and three children in 2021. ("one-child policy - Consequences of China's one-child policy | Britannica")

Underpopulation puts a strain not only on economic performance but also on military power. Three crucial factors are needed to build and maintain a country's military strength: manpower, money, and technical experts. Traditionally, higher-populated countries have more substantial national power credited to their more extensive pool of young citizens eligible for military service. Depending on certain military operations, such as defending against raids, a higher amount of manpower allows the capability to mobilize countervailing forces fast enough to repel raiders. However, manpower is no longer the main factor determining a country's military power because money and technical experts have increasingly played essential roles in conventional warfare from the beginning of the Industrial Revolution to today's Information Age. Military operations such as controlling the commons (e.g., seas, air, space, cyberspace) require money for modern equipment and skilled experts rather than manpower. As suggested by Dr. Azar Gat's work, "the best measure of a great power's military power is provided by the product of a nation's GDP with the square or third root of its GDP per capita." ("CHAPTER SIX The Impact of Demographic Trends on Military Power Projection" 89-110). To avoid war and maintain quality of life, addressing underpopulation is necessary for national sovereignty.

Overpopulation 

Overpopulation is defined as the situation when resources used each year by the world population are unable to regenerate every year. While underpopulation poses an economic and national threat, if not addressed quickly, overpopulation can also result in economic decline and irreversible environmental damage, making the Earth uninhabitable. Since the Industrial Revolution (and after World War II), to accommodate consumerism, developed nations have industrialized the natural world. Significantly altering Earth's biosphere into urban or industrial areas for jobs, living spaces, and consumer products lead to "..deforestation, decreased biodiversity, and spikes in pollution and emissions, which will exacerbate climate change." (Bish). 

As countries welcomed the post-World War II economic expansion, they did not see the consequences of human activities devastating Earth's climate. Climate change refers to "long-term shifts in temperature and weather patterns." ("What Is Climate Change? | United Nations"). Since 650,000 years ago, Earth has gone through seven different ice ages, corresponding to seven cycles of carbon dioxide levels. Until 1950, carbon dioxide levels had never surpassed 300 parts per million. Today, it has reached 400 parts per million and shows no sign of declining. Natural resources such as fossil fuels are exploited for human activity, emitting carbon dioxide, a greenhouse gas, resulting in the warming of Earth's temperatures. 

Greenhouse gas emissions are the result of human activities from deforestation, land use changes, and burning fossil fuels, trapping infrared energy inside the Earth's atmosphere. Since the beginning of the Industrial Revolution, human activities have contributed to the increased carbon dioxide concentration by 48%. Earth's surface temperatures have increased by 2 degrees Fahrenheit (1 degree Celsius) since the late 19th century ("What Is Climate Change? | United Nations") and oceans by 0.6 degrees Fahrenheit (0.33 degrees Celsius), with future forecasts of an increase between 2.5-10 degrees Fahrenheit in the next century. Other consequences include but are not limited to reduced crops, stronger hurricanes, and heat waves, making Earth uninhabitable.

Another effect of overpopulation is the increased spread of infectious diseases. Increased population aided the spread of lethal diseases such as bubonic plague, cholera, influenza, Ebola, and COVID-19. A pandemic is an outbreak of an infectious disease that kills many people on a global scale. With today's interconnected global economy, diseases spread quickly, affecting public health and causing short-term and long-term economic impacts. As in the case of Ebola, the economically active population was mainly affected, bringing about an increase in public health expenditures and an economic slowdown from a decline in consumer spending and tax revenue. In 2014-2015, Liberia experienced a rise in public health expenditures and national deficits of 8.5% of GDP. ("2014-2015 West Africa Ebola Crisis: Impact Update"). Workforce-market implosion, less trade and transportation, closed workplaces and land borders, and reduced tourism played a part in the epidemic's economic decline.

Why are extreme changes in the population an existential threat, and what can we do to prevent it?

Regardless of the direction of population changes, it imposes an existential threat to humanity. Underpopulation threatens economic decline, leading to a lower standard of living and irreversible effects on a country if policies are not flexible to reverse change quickly. Not being able to replace the population will inevitably result in humankind's loss. One of the ways to encourage childbearing is to loosen policies that punish having children and incentivize having children and larger families. By promoting gender equality, women do not have to give up their careers. An improved childcare system can help reduce the cost of raising children and allows women to stay in the workforce. As cultural norms change and women desire to have fewer children, increasing immigration to combat dropping birth rates can ensure population stability.

On the other hand, overpopulation can bring death to our planet by spreading a disease or causing irreversible ecological degradation. Increasing female education will delay childbearing age while increasing the workforce. Preventing another baby boom, as in the case of post-World War II, will prevent a disproportionate age distribution of a smaller 15-65 age group and a larger dependent under-15 and over-65 group. If this is to happen, countries should adopt "sensible pro-growth economic policies, [and] 'the demographic bonus' ought to translate into a jump in income per capita." The Asian Tigers (Korea, Singapore, Taiwan, and Thailand) successfully demonstrated these policies (Sinding).

Closing

It is essential to acknowledge the effects of population changes by understanding the existential threat they bring to our global society. To address underpopulation, we need to acknowledge changes in cultural norms by incentivizing childbearing and improving childcare systems. To address overpopulation, we need to form effective economic policies to promote economic growth based on increasing the workforce, empowering women, and providing education for all. As we look to the future, we need to spread awareness that these effects are becoming a plausible threat to all life on Earth so that society can function and thrive in the future.

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