1.5 Human Population and Sustainability

Human Population

The study of population has never been more important than it is today. We are close to 8 billion people on the planet, but most of this growth has occurred in the last 100 years, in developing nations. With a projected population growth of between 9-11 billion by 2050 and the effects of climate change on the environment, we can reasonably expect the impact of geological disasters to be greater.

The overall purpose of this section is to introduce the population distribution and population growth issues that can exacerbate geological processes and turn them into disasters and catastrophes. This course emphasizes a geographic perspective on population growth as a relative concept. This section also identifies the main reasons why people migrate over time: economic, political, cultural, and environmental.

Population Growth

The study of the human population has never been more critical than it is today. There are close to 8 billion people on the planet, but most of this growth has occurred in the last 100 years, mostly in developing nations. Humans do not live uniformly around the world, but in clusters because of the earth’s physical geography. Environments that are too dry, wet, cold, or mountainous create a variety of limiting factors for humans. Two-thirds of the world’s population is within three significant clusters: East Asia (China), South Asia (India and Indonesia, and Europe, with the majority in East and South Asia.

Video 1.5.1 How did we get so big so fast? (2:38). Our population reached 7 billion in 2011. Several videos brought awareness of this fact. Watch this demonstration that uses water and dripping vessels to simulate our population to try to answer, how did we get here?  Note, in 2022 we are reaching the 8 billion count.


Neither people nor resources are distributed uniformly across Earth. Regarding population growth, geographers emphasize three elements: the population size, the rate of increase of world population, and the unequal distribution of population growth. Geographers seek to explain the patterns that exist and the changes between the patterns.

Human geography emphasizes a geographic perspective on population growth as a relative concept. Human-environment interaction and overpopulation can be discussed in the contexts of , the availability of Earth’s resources, and the relationship between people and resources.

Demographers, scientists that study population issues, and other scientists say there is more to the story than pure population growth. Ecologists believe that humans have outgrown the Earth’s . There are not enough of the world’s resources to give every human a standard of living expected by most Americans. If all the people on the planet lived the average American lifestyle, it would require over three Earths, some people calculate five Earths. But, if we were to live as a Bangladeshi villagers then our planet could sustain 15 to 20 billion people (Eisntein, 2019). This means that “How we live is at least as important as how many we are” (Einstein, 2019).  As of March 22, the United States Census Bureau estimates that the world population is nearly 7.9 billion, with a growth rate of roughly 1.07 percent, or roughly 82 million people per year. The world population reached 6 billion in 1999 and 7 billion in 2011. If the current growth rate continues, the human population will reach 8 billion by 2023 and hopefully level off at roughly 10 billion by 2055. Between 2010 and 2050, world population growth will be generated mostly in developing countries. But will we ever get to 11 billion?

Video 1.5.2 Why the world population won’t exceed 11 billion (16:36).  In this segment of one of his lectures, famous Professor Hans Rosling uses statistics to summarize population growth and explains why the total human population will never reach 11 billion, as others predict and fear. 

Distribution of the World’s Population

Geography is a significant factor in population distribution. Humans only occupy five percent of the Earth’s surface because oceans, deserts, rainforests, and glaciers cover much of the planet. Humans cannot live in many parts of the world due to moisture, temperature, or growing season issues. For example, 20 percent of the world is too dry to support humans. This mostly has to do with high-pressure systems around 30 degrees north and south of the equator where constant sunny conditions have created some of the world’s largest deserts. Some of these include the Sahara, Arabian Peninsula, Thar, Takla Makan, and Gobi deserts. Most deserts do not provide enough moisture to support agriculture for large populations.

Regions that receive too much moisture also cause problems for human settlement. These are tropical rainforest regions located between the Tropic of Cancer (23.5 degrees North) and the Tropic of Capricorn (23.5 degrees South). The problem with these regions of the world has to do with the soil erosion due to high precipitation. High levels of precipitation hinder agricultural production because nutrients in the soil are washed away. This is partly why slash-and-burn agriculture occurs in these regions. Locals will burn part of the forest to put nutrients back into the ground. This only works for a short period because the precipitation washes away nutrients within a few years, so farmers move on to other parts of the forest with their slash-and-burn practices.

Additionally, regions that are too cold pose problems for large population clusters and food production. The cold Polar Regions have a short growing season, and many of the Polar Regions have limited amounts of moisture because they are covered by high- pressure systems (much like the desert regions). Thus, cold polar regions experience low temperatures and lack of moisture, despite access to snow, ice, and glaciers. Mountainous and highland regions lack population clusters due to steep slopes, snow and ice cover, and short growing seasons.

The term for areas where humans permanently settle is ecumene. Population growth and technology explode the ecumene of humans, which affects the world’s ecosystems.

Future of Population Growth: Ethics and Politics

What is overpopulation? Most people equate overpopulation with crowding, but, in fact, density is irrelevant to questions of overpopulation. or example, we could pack all ~8 billion humans in California, but that is not desirable, sanitary, or sustainable. What is relevant is carrying capacity. We overpopulate an area when its long-term carrying capacity is being degraded by its current human occupants.

How many people can the earth support? That depends on people’s lifestyles, which affects the rates at which they consume resources. In more affluent countries, people consume resources at a greater pace, residents eat a diet with more animal products, use more energy in homes, and produce more goods. So, if everyone lived as they do in wealthier countries, Earth’s resources could support fewer people than the number currently living on the planet today. The average rates at which people consume resources like oil and metals, and produce wastes like plastics and greenhouse gases, are about 32 times higher in North America, Western Europe, Japan, and Australia than they are in the developing world. In the least developed countries, people use fewer resources but often suffer from malnutrition and fewer opportunities to lead healthy lives and contribute to their nation’s economy.

Global demand for natural resources has doubled in the past 50 years. Our ecological footprint is a measure of how fast we consume resources and generate waste compared to how fast nature can absorb our waste and generate new resources. Scientists calculated that since the 1970s, our demand for resources has exceeded what the earth can regenerate in a year. It now takes 1.6 years to regenerate what we use in one year. Rather than consider how many people could live on Earth, we should consider a sustainable balance of people and resources that raises the standard of living around the globe without degrading the environment.

Video 1.5.3 Learn about an infamous overpopulation bet between two demographers (4:48).

Global Population Trends

A region’s population will grow as long as its crude birth rates are higher than its crude death rates. A crude birth rate (CBR) is the total number of live births for every 1,000 people in a given year. So, a crude birth rate of 10 would mean ten babies are born every year for every 1,000 people in that region. Crude death rates (CDR) are the total number of deaths per 1,000 people in a year.

When comparing CBRs to CDRs, a region’s natural increase rate can be determined. A natural increase rate (NIR) is the percent a population will grow per year, excluding annual migration. Usually, an NIR of 2.1 is required to maintain or stabilize a region’s population. Any more than that and the population will grow, any less than a NIR of 2.1 causes population contraction. The reason the NIR percent is 2.1 and not 2.0 for stability is because not every human will pair up and have a child because of genetics, choice, or death before childbearing years. Once we know the NIR, we can determine the doubling time. Doubling time is how many years it would take for a defined population to double, assuming that NIR stays the same over time. Currently, about 82 million people are added to the world’s global population every year.

A useful tool used by scientists that focus on demographics is a population profile, also called a population pyramid. A population profile visually shows a particular region’s demographic structure concerning males and females and is often expressed in numbers or percentages.

Video 1.5.4 The population pyramid explained (5:00)

Environmental Impacts

There are many ways in which our large and growing human population impacts the global environment. Using resources faster than natural processes can replenish them is just part of the issue. Over the past 50 years, humans have altered ecosystems more rapidly and extensively than in any other comparable period in history, primarily to meet the rapidly growing demands for food, freshwater, timber, fiber, and fuel.

Climate Change: Our global temperature is on the rise due to the ever-increasing amount of greenhouse gases that are emitted through human activities, including fossil fuel use, deforestation, and livestock grazing. This warming is causing sea-level rise from Arctic ice melt, more extreme weather, and loss of habitat, including coral reefs. Population growth only exacerbates climate change, as more people demand more food and energy. With renewable energy supplying only a small fraction of total energy use, fossil fuel use is expected to expand for the foreseeable future.

Water Scarcity: About 35 percent of the world’s people already face chronic water shortages. As the population grows, we need more water for agriculture and industry, as well as for domestic uses. A child born in the developed world consumes 30-50 times as much water as one born in the developing world. The worldwide supply of clean, accessible water is further reduced by pollution. In 2017, over 785 million people lacked access to basic water and sanitation services and over 884 million people did not have safe water to drink (CDC).

Biodiversity Loss: Nearly all the world’s ecosystems are shrinking to make way for more humans and their homes, farms, factories, and shopping centers. Globally, 13 million hectares of forest (about the size of Costa Rica) were lost each year from 2000 to 2010, as much of it was cleared or degraded by human activities. Forests play an important part in climate change mitigation. Forests store a vast amount of carbon. When we cut down a forest to convert it for another use, we release carbon back into the atmosphere. The World Wildlife Fund’s Living Planet Index shows a 30 percent decline in Earth’s biodiversity since 1970; a 60 percent decline in the tropics. According to the World Conservation Union, 1 in 3 amphibians, 1 in 4 mammals, 1 in 8 seabirds, and 70 percent of plants are at risk of extinction due primarily to human alteration of their habitats.8 Humans depend on rich biodiversity for survival—food, medicines, climate regulation, and more.

Unnatural Disasters

Former UN Security General Kofi Annan has said, “The term natural disaster has become a misnomer increasingly. Human behavior transforms natural hazards into unnatural disasters.” Most deaths from natural disasters occur in less developed countries. According to the United Nations, a less developed country (LDC) is a country that exhibits the lowest indicators of socioeconomic development and is ranked among the lowest on the Human Development Index. Those who live in low-income environments tend to have the following characteristics:

  • Live in areas that are at a higher risk of geologic, weather, and climate-related disasters
  • live in areas that lack the economics and resources to provide a safe living infrastructure for its people
  • have few social and economic assets and a weak social safety net, and
  • lack the technological infrastructure to provide early warning systems

As human populations have grown and expanded, and technology has allowed us to manipulate the environment, natural disasters have become more complex and arguably more “unnatural.” There are a variety of ways humans have not only influenced but magnified the impacts of disasters on society. For simplification, this book will narrow it down to four: human population growth, poverty and inequality, environmental degradation, and climate change.

Video 1.5.5 What do we mean when we talk about development? (2:40).

What Will the Future Hold for People and the Planet?

We could achieve sustainability if the population stabilizes, if we use resources more efficiently and redistribute them uniformly and if we learn to live within the means of this planet. The good news is that the very conditions that will help the population stabilize are those that help people live longer, healthier lives, raise healthier children, and enjoy greater prosperity. These include universal education and gender equality, access to reproductive health care, and family planning services. Achieving ecologically sustainable lifestyles will take ingenuity and a sense of shared responsibility for the ecosystems that sustain us all. Richer nations will need to reduce their large footprints and emerging economies will need to find new models of growth to improve their citizens’ well-being in ecologically sustainable ways.


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Dynamic Planet: Exploring Geological Disasters and Environmental Change by Charlene Estrada, Carolina Michele Londono, Merry Wilson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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