POP: Lesson - Human Population Dynamics (Topic 3.8) 📖

⏳ Estimated Reading/Watching Time: 33 - 35 minutes

Explain how human populations experience growth and decline.

Demographics

Most environmental problems are caused by the rapidly growing human population. In January 2024, the population was 8.1 billion. The human population is expected to increase to around 10 billion by 2057.

Population growth is not the same in every country or every region, however. Currently, growth is slowing in developed nations, while many developing countries are still growing at an astounding rate.

Studying the statistical change in human populations and applying the concepts of population ecology to human populations is called demography. By studying the size, density, distribution, sex ratios, age structure, birth and death rates, and movement of people, a demographer can help to predict shifts in populations and potential environmental consequences throughout the world.

As of January 2024, the most populous nation, China, has approximately 1.426+ billion people; India is 2^nd with about 1.429+ billion people and the USA is third with approximately 339+ million people. China has been the world’s most populous country for a long time, but the UN estimates that India will be the world’s most populous country by 2024 because India's population has a +0.81% growth rate and China has a -0.02% growth rate.

China and India are considered developing nations but are continuing to move toward "developed" nation status due to increased job growth and opportunities. The environmental impact of both countries is quite large, but with more and more people having the means to consume and the desire to have materials that improve their own lifestyles, the effect on the environment will be even more dramatic and humans will continue to move closer to the carrying capacity of the Earth.

Demographics is an incredibly interesting field of study. For example, a demographer might look at the graph below and try to understand why certain countries have high birth rates, death rates, or both. Once we know the cause(s), we can start brainstorming solutions.

Our population hasn't always grown like this. In fact, for many, many years it was quite stable. Watch the video below to learn more about how our population has changed through the years:

Let's go back and look at the human population through the ages before we move forward.

Historical Human Population Growth

200,000 years ago

Hunter Gatherers

Around 200,000 years ago modern humans most likely arose in Africa. Around 40,000 years ago, fully modern humans appeared in Europe during a period known as the Paleolithic. These humans were small, hunter-gatherer tribes. They were constantly moving around looking for food and shelter. The human population was relatively stable.

Around 12,000 years ago humans in the Middle East began to develop animal husbandry and agriculture. This allowed humans to stop their nomadic ways and create towns. Because they weren’t constantly on the move, they were able to devote time to things like creating civilizations and population growth. This is when the human population began to grow.

12th Century

Middle Ages

During the 12th century, the human population experienced a dip in the population. This was due to the Black Plague. During this time there was little sanitation and people did not understand the cause of diseases. The Black Plague, carried by rats, infected the human population and spread like wildfire.

the world population size over 12,000 years based on HYDE and UN estimates. it features a red line representing population in billions from 10,000 BCE to 2019. The x-axis represents time in years, and the y-axis shows population in billions. The graph shows a gradual increase for millennia followed by a recent rapid ascent. Notable points include 4 million in 10,000 BCE, 190 million in year 0, 600 million in 1700, 2 billion in 1928, 3 billion in 1960, and 7.7 billion in 2019. Additionally, it notes an average growth rate from 10,000 BCE to 1700 of 0.04% per year. — **For many thousands of years, the human population remained quite steady. Then, in the late 1800s and early 1900s, the human population started increasing exponentially.**

17th-18th Centuries

Industrial Revolution

In the 17th and 18th centuries, modern science and technology began to appear. Humans started using fossil fuels to power cities. This allowed us to produce more food to support more people. During this time, high reproductive rates were balanced by high mortality. Many children died and not many people survived to old age. By 1804, there were 1 billion people on the planet.

In the late 1800s, Pasteur and others demonstrated that diseases were caused by infections. Scientists developed vaccines that reduced mortality and towns began treating their sewage and drinking water, reducing the spread of waterborne diseases. Humans also started eating more nutritiously.

1940s - 1960s

Modern Times

During World War II, we developed chemical pesticides and high-yield crops. We increased our irrigation and fertilizer use. There were significant environmental costs associated with industrialized agriculture and overuse of pesticides. We will discuss these environmental costs later in this course.

After World War II, we experienced a "baby boom" between the mid-1940s and the mid-1960s. As young men returned home from the war, they started families, increasing the birth rate during this time. However, due to previous low birth rates and pre-modern healthcare, the top of the global population pyramid remained narrow. For example, more than 1 in 5 children born in 1950 died before they reached the age of 5.

What is the Human Population's Carrying Capacity?

The human population has experienced exponential growth, especially since the Industrial Revolution. This has caused many to wonder if the human population has a carrying capacity and what the carrying capacity for the human population might be. The best estimates so far are around 7.7 billion people if we continue at our current rate of resource use. However, we are already over 8 billion. Some scientists suspect that we are already over our carrying capacity!

The population pyramid depicts men on the left and women on the right, spanning ages from 10 to 100 years in ten-year intervals. The pyramid widens significantly for younger age groups in earlier years, indicating a larger young population, and narrows for future projections, suggesting an aging population. — Previously, our population pyramid resembled that of a developing country, with a wide base and a narrow top. More recently, however, our global population pyramid has begun to look more like a developed country, or a country with slow growth.

Thankfully, world population growth has slowed in recent years, though it is still growing! The annual growth rate reached its peak in the late 1960s when it was at 2% and above. The rate of increase has therefore almost halved since its peak of 2.19 %, which was reached in 1963, to the current 1.15%. The annual growth rate is currently declining and is projected to continue to decline in the coming years, but the pace of the future change is uncertain. Currently, it is estimated that it will become less than 1% by 2020 and less than 0.5% by 2050.

This means that the world population will continue to grow in the 21st century but at a slower rate compared to the recent past. Several factors account for this continued growth:

Population momentum from the earlier high birth rate cohorts continues to affect the human population (we will discuss this below!).
Healthcare has improved. For example, less than 1 in 20 babies born today die before they reach age 5. So, while fewer babies are being born, more are surviving past childhood and into old age.

UN projections indicate that the world population has doubled (100% increase) in 40 years from 1959 (3 billion) to 1999 (6 billion). In 2011, the global population reached the 7 billion mark, and in January 2024, it was just over 8 billion. The world population is expected to grow to around 10 billion by 2057, and 10.4 billion by 2100.

Use the graphic below to explore global population growth rates since 1950.

We know from our studies of environmental science thus far that exponential populations experience a crash once they exceed their carrying capacity. If we truly are in overshoot, when will the crash come? This is a question no one knows the answer to, but we can estimate and predict based on our current resource use.

Populations cannot continue growing exponentially forever – they will exhaust their resources. Scientists are working now to figure out ways to extend our carrying capacity by high(er) yield crops, more efficient agriculture, having human residences grow upwards rather than outwards (less land per human), and even the possibility of living on other planets!

Essential Knowledge

Factors limiting global human population include the Earth's carrying capacity and the basic factors that limit human population growth as set forth by Malthusian theory.

Density-Dependent Impacts

The distribution of the human population is considered to be clumped, with more people living in regions with climates that are tropical, subtropical, or temperate. Such locations include China, India, Europe, and Mexico. Populations are also the densest near water, whether freshwater or saltwater. More people living in a particular area means there is more of an impact on the environment from use and pollution in that area. We call these density-dependent impacts because they are exacerbated as density increases.

Explore the different density-dependent impacts our growing human population has on the Earth. Which do you think is the most pressing? Why?

Resource Use

As the population increases, we require more and more resources. Already, agricultural areas occupy around 38% of the land on the planet. You will soon learn that not many environments are suitable to agriculture, so not every environment should be converted into agricultural areas. As we use more and more land for agricultural purposes for our growing population, we will also need more land for homes and shelter. Eventually, we will run out of land suitable for agriculture and living.

The video below describes some of the problems we are facing regarding the lack of agricultural land needed to feed our growing population and also some solutions for the future:

As our population grows, we also use more and more water. Agriculture and industry use the most water and as populations increase, agriculture and industry will as well. If we start cultivating dry lands for agriculture, we will need even more water. Most of the water on the planet is salt water, so we will have to find new ways to purify water and water will become increasingly more expensive.

Energy Use

As our population increases, our energy use will also increase. We use energy to power our vehicles, industries, homes, and anything else that needs power.

The graph depicts the relationship between CO2 emissions per capita and GDP per capita for different countries in 2020. Colored circles denote countries from various continents, sized according to population. A labeled area in the bottom right corner illustrates the goal of attaining energy access with net-zero CO2 emissions. — It is a fine line between not having access to energy to live a modern lifestyle and using so much energy that it is unsustainable. Energy use is directly tied to our global population because the more people we have, the more energy that is used.

Currently, the bulk of our energy comes from fossil fuels. However, we are quickly depleting our stores of fossil fuels, so we will need to diversify our energy use, whether that means nuclear, hydroelectric, solar, wind, or a combination of these.

Habitat Loss

Humans are increasingly destroying natural habitats to build shopping malls, homes, factories, power plants, and highways, to name a few. When we cut down a forest or drain a wetland to build something or plant crops or raise animals for food, we reduce the amount of space natural populations have to live. Those species that need large areas to survive or don’t do well with human intervention, tend to become endangered or extinct.

The countries most at risk of losing more than 20% of their habitat are also countries that have the fastest growing populations:

Human interference also reduces biodiversity because we tend to lose these species. Even though only a few species may be lost because of the reduction in habitat, the loss of these species can have wide-ranging effects throughout the environment (trophic cascade).

Pollution

With our increasing industry, agriculture, and activities like driving vehicles, we are polluting the planet at an ever-faster rate. When we drive our vehicles, we are emitting CO₂, NO_x, SO_x, and a host of other pollutants into the environment.

When we fertilize our lawns or agricultural fields, the fertilizers run off into our waterways and sink down into the aquifer. Almost everything we do pollutes the environment somehow.

More and more trash is ending up in our oceans and plastic is polluting the terrestrial and aquatic environments.

We have oil spills, nuclear disasters, air quality issues from burning fossil fuels, etc.

All of this is intensified by an increasing human population.

Waste

Each person on the planet produces waste. Some people and countries produce more than others, but everyone produces waste. The more people we have on the planet, the more waste we have.

The graph below compares how plastic waste is treated across different areas of the world. However, plastic waste is not the only waste we produce. We also produce food, electronics, paper, metal, and other types of waste in our homes and commercially:

As our waste increases, we have to find places to store all of this waste. If we burn it, we will release fumes and CO₂ into the atmosphere, which will intensify global warming. If we bury it in landfills, we only have so much space to put it before new landfills must be created. Some have suggested sending the waste into space, but that is a very expensive proposition, and do we have a right to pollute outer space? Some have also suggested sending waste to the bottom of the ocean in sealed containers, but can we trust that the containers will stay sealed? Is it a good idea to literally fill up the ocean with trash?

All of these problems are serious, but they also exemplify why the study of environmental science is so important. As we learn more about how the environment and humans are interconnected and some of the harmful effects we have had on the environment, we can make better choices and educate others to do the same.

Essential Knowledge

Population growth can be affected by density-dependent factors, such as access to clean water and air, food availability, disease transmission, or territory size.

Density-Independent Impacts

The graph displays global deaths from various natural disasters over a century. n the 20th century, millions died, primarily from floods, droughts, and famines. In the 21st century, death tolls decreased, except for large-scale events like the 2004 Indian Ocean tsunami, 2010 Haiti earthquake, and 2020 COVID-19 pandemic. — Natural disasters are generally considered density-independent because they aren't exacerbated when density increases, where resource use and pollution get worse with increasing density. However, the more people you have living in an area affected by a natural disaster, the larger the human and economic costs.

Density-independent factors are those that limit population growth regardless of the density of the population. For example, air pollution increases as human population density increases. However, a volcanic eruption will happen regardless of how many people are living in an area.

Open each tab below to see how natural disasters can affect the human population:

🧳 Displacement and Migration (click to reveal)

Extreme weather and natural disasters can force people to leave their homes before, during, and after the event. This creates challenges for host communities and the displaced people as the communities' struggle with overcrowding, poverty, unemployment, social conflicts. For example, more than 11 million people were displaced by floods in Pakistan in 2010.

Extreme weather and natural disasters can increase exposure to infectious diseases, heat stress, respiratory problems, injuries, and mental health issues, affecting the productivity and quality of life of the population. For example, after Hurricane Maria in 2017, there were widespread power outages and sewage leaks in Puerto Rico, which affected the availability of clean water. People who suffer from chronic diseases might have trouble accessing healthcare facilities or supplies.

🦠 Health Risks (click to reveal)

Extreme weather and natural disasters can damage crops and livestock, reduce water availability and quality, and disrupt food supply chains, leading to malnutrition, hunger, and famine. For example, after Hurricane Sandy in 2012 there were widespread power outages. During this time, many farmers faced losses due to spoilage or theft of their produce. These losses disrupted the food supply chain, increasing the cost of food until agricultural operations could recover.

🍽️ Food Insecurity (click to reveal)

When natural disasters occur near human populations (which is pretty much everywhere!), much infrastructure is destroyed or needs significant repairs. People can be displaced and be out of work, businesses must close until they can make necessary repairs (or completely rebuild), power is often out for many days or weeks, which requires additional workers to help restore power. All of this has a cost. Recent data suggest that extreme weather events account for 77% of total economic losses.

💸 Economic Losses (click to reveal)

When a natural disaster hits a human population, infrastructure is often destroyed. This infrastructure is often spread around the environment. For example, a tornado might pick up debris and place it in a natural area. A hurricane might wash chemicals or debris into the coastal ocean, affecting the health of the marine environment. After the earthquake that hit the Fukushima nuclear power facility in Japan, radioactive waste washed into the ocean and made it as far as California!

🌱 Environmental Degradation (click to reveal)

Humans can exacerbate these events. For example, earthquakes are natural phenomena, but we have seen increased numbers of earthquakes in areas where hydraulic fracking is occurring. And as climate change becomes more intense, hurricanes and other storm events become more frequent. So, while increasing human populations are not directly causing natural disasters, they can still become more frequent due to our actions.

Now that we have early warning systems in place and build our infrastructure to withstand many of these disasters, the human toll from each event is much less. However, the ecological and economic effects of natural disasters can be extreme. For example, it is estimated that Hurricane Katrina (2005) caused 170 billion dollars in damages, making it the costliest US Hurricane ever. Hurricane Ian hit in 2022 and estimates project it will cost as much as 87 billion dollars in damages, as repairs are ongoing (as of January 2024).

Essential Knowledge

Population growth can be affected by density-independent factors, such as major storms, fires, heat waves, or droughts.

Doubling Time and The Rule of 70

Doubling time is the time it takes something to double. If the population is growing quickly, the doubling time will be short. If the population is growing slowly, the doubling time will be long. This is known as an inverse relationship. For example, in 1830, the human population reached 1 billion. By 1930, the human population reached 2 billion. At this time, the doubling time of the human population was 100 years. By 1975, the human population reached 4 billion. So, the doubling time of the population had changed to 45 years!

For the human population (and most other populations), we do not want a shorter doubling time. This means that the population is growing quickly and will likely outstrip its resources soon.

The Rule of 70 allows us to estimate the number of years it takes a population to double.

Doubling time in years = 70 ➗ % growth rate

Watch the video below to learn how to calculate doubling time from the growth rate:

Essential Knowledge

The rule of 70 states that dividing the number 70 by the percentage population growth rate approximates the population's doubling time.

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AP Exam Tip

You will need to know how to calculate doubling time on the AP exam.

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