Human Overpopulation: Causes, Effects, Problems & Solutions

Human overpopulation is an issue by itself, but can also be at the core of other key environmental and social issues.

It makes sense – more people generally means more consumption (of food, water, natural resources etc.), more waste generated, and more environmental pollution issues. 

In this guide, we discuss the causes, effects, problems and potential solutions behind overpopulation.


(Note – this guide includes general information on human overpopulation, and is a ‘starter’ type resource only. It is not a definitive guide for the issue of overpopulation)


Summary – Human Overpopulation

One way to describe human overpopulation is the point at which the number of humans in an area, region, city, country, or the world at large, cannot be maintained

This might occur because there is not enough resources to support that number of humans, or because the man made systems or natural environment begin to degrade or deplete in terms of ability/capacity to support those humans

[Although – there is a difference between supporting a population’s basic needs, and supporting all consumer choices – which might be excessive, and/or unsustainable]

So, there can really be two parts to overpopulation that can work in conjunction with each other:

1. The size (and growth or shrinking) of the population

And, 2. How effectively and sustainably that population can be supported (by existing resources and environment, and the ability to through new resource creation to meet future demand)


A smaller or stagnating population could face issues if they consume at an unsustainable rate, degrade their environment at an unsustainable rate, or run out of or don’t have access to resources

The number of humans in one area at one time can increase because of a number of reasons, but some of the main reasons might include increased birth rates, decrease in the mortality/death rates, and increase in immigration

Historically, technological revolutions or advances in technologies have also increased populations e.g. the tool-making revolution, the agricultural revolution, and the industrial revolution – all of which allowed humans more access to food, resulting in subsequent population explosions

The fertility rate is said to be strongly influenced by cultural and social norms that are rather stable, and therefore slow to adapt to changes in the social, technological, or environmental conditions

Population increase rates tend to be highest in areas where children die young, where there is poverty (especially extreme poverty), and where there is lack of access to education

Religious and ideological opposition to birth control has been cited as a factor contributing to overpopulation and poverty

Guatemala is an example of a country whose average family size halved with the decrease in extreme poverty.

Cambodia and Namibia are two countries who have experienced similar trends

Globally, populations in some of the poorest countries in the world are expected to double and even triple by 2040-50

Overpopulation in lower income countries might be seen as undesirable as economic development falls far behind a point where there is proper capital available to invest in the people and the country to support them.

If you add mismanagement on the government level, corruption and a lack of effective social and governmental systems – problems can become worse

A quickly growing population, or a population size that is already too big, can place a strain on already depleting or stressed resources. One example of this is a city’s water supply

Over population can mean more resources are needed by a population as a whole, but also more waste is produced, and there is more pollution and environmental degradation as a flow on result.

As a few examples … an increasing population might mean more water is required for food/agriculture and energy production in the future, more waste such as plastic is generated, and there is more water pollution, air pollution, soil/land pollution and general waste and environmental pollution

Economically, with overpopulation, there might be more consumers and employees/skills introduced to the economy, and the economy could grow in some ways overall, but there may also be more labor and more competition for jobs

Increasing populations aren’t always the sole cause of other social or environmental issues. One example of this is greenhouse gas emissions – they can be increased by other related or unrelated factors such as rate of economic growth and industrialisation, total consumption and consumption rate per capita, a city’s energy mix and energy carbon intensity, and how key industries such as electricity production, transport and agriculture operate 

The effects of overpopulation can be compounded by overconsumption, broken or inefficient social and governmental systems, ineffective technology, environmental pollution and degradation, and other factors

A growing population or a large population isn’t always a negative – there can be positives as well

Technology and stage of economic development can play a large role in providing enough resources for a population e.g. look at the difference between agricultural sectors in developing vs developed countries, as well as the capacity to produce electricity, provide cold food storage, and so on

But, even in developed countries and cities, there can be supply issues related to population.

Perth in Western Australia is a dry city, but faces many of the same challenges as Cape Town (dry city, increasing population, prone to droughts).

Perth was able to provide enough freshwater and Cape Town experienced a water shortage because of various factors like good governmental planning, investment in water treatment and recycling, investment in desalination plants and so on.

The US across many measures (along with other developed countries) consume far more resources per capita than many poorer countries, and produce more waste per capita as well

The most overpopulated cities tend to be in developing countries where poverty is rampant due to this overcrowding (leading to potential problems like sickness, disease, death and so on).

Identifying overcrowded cities in underdeveloped regions, in terms of number of people per square area and income per capita, can help

Even in developed countries, heavily populated cities might deal with intense smog and pollution problems that exacerbate health and poverty issues.

Labor prices can also start to diminish with an increase in labor

Solutions to overpopulation might include reducing poverty, lifting education rates, increasing the quality of health care and safety (especially for children), and investing in basic living resources for the poorest countries, or countries with the highest fertility and population increase rates

Other general solutions might include investing in technology to provide the most crucial resources for a basic standard of living for a population, becoming clear on exactly how many people each city in the world can sustainably support with the technology, resources and systems they currently have available, more education and access to healthcare for women in regards to pregnancy, more effective education for men on contraception, enforcing birth laws/regulations for the most heavily populated and quickest growing cities and countries where there’s an unsustainable increasing population or large population, and to examine our consumption and waste habits city by city.

Cities might focus on quality of life as a measurement, in addition to how many people an individual city or geographic area can support (carrying capacity of a region)

Each city has it’s own capabilities and carrying capacity to support different populations to different extents – it’s too general to examine overpopulation at the country or state/province level

Some people have suggested space colonization and making use of resources in space as an additional option in the future for further human population expansion

Some experts say that science and technology alone can’t help us fix some overpopulation problems, and a cultural-social-political shift will be needed instead 

The world’s population currently sits at around 7 billion in 2019, and is forecasted to reach somewhere between 9 to 13 billion between 2050 to 2100 

Most of the world’s expected population increase [in the future] will be in Africa and Southern Asia.

Africa’s population is expected to rise from the current one billion to four billion by 2100, and Asia could add another billion in the same period. [So, we might focus on these regions specifically]

Almost all growth [in future population] will take place in the less developed regions, where today’s 5.3 billion population of underdeveloped countries is expected to increase to 7.8 billion in 2050.

By contrast, the population of the more developed regions will remain mostly unchanged, at 1.2 billion. An exception is the United States population, which is expected to increase by 44% from 2008 to 2050 (

When you look at current birth rates – these forecasts make sense.

The least developed regions in the world have far higher birth rates than developed regions.

As the least developed countries grow their economies in the future, birth rates are expected to fall, but to still outpace the most developed countries.

A theoretical question to ask might be ‘With current technology, science, natural resources and environmental conditions – what population number can the world, and individual countries and cities sustain? What would the standard and quality of living be at that number? What factors and considerations are this number based on?’

Another theoretical question to ask might be ‘What is going to be the result of population growth at the current rate to 2050, 2100, and beyond?’

There is more information in this guide about whether humans and Earth might run out of resources in the future, and what might happen if we do


What Is Human Overpopulation?

Human overpopulation is different to population growth.

Population growth can happen to any size of population, and the environment and resources are not taken into account.

But, overpopulation specifically involves:

– … the ecological footprint of a human population in a specific geographical location exceeding the carrying capacity of that location

– [it usually involves the] rapid depletion of non-renewable resources or … degradation of the capacity of the environment [in the long term]


So, it relates specifically to how a geographical area can provide adequate resources in the short and long term for the population that inhabits it.

In the modern globalized world with importing and exporting resources into and out of cities and countries, overpopulation might be assessed on an increasingly wider scale.


Causes of Human Overpopulation

Some of the causes of overpopulation might include:

– an increased or high birth/fertility rate

– a decline in the mortality rate

– an increase in immigration

– degradation of the natural environment by humans

– use of, or management of natural and non renewable resources by humans that depletes these resources

– the inability to generate or create new resources to meet demand

– the inability to prevent or reverse degradation of the environment in different ways, in accordance with what is sustainable

– an environment that is naturally unsuitable for human livelihood (such as a very dry climate, or a region with poor soil or land), or an area with a lack of natural resources, or poor access to natural resources. In this instance, the natural conditions are more the problem rather than human behavior


So, there’s really the population component, the management of the existing environment and resources component, and the component relating to what can be done in the future to meet carrying capacity requirements (such as generate new resources – desalination may be one example of technology that addresses fresh water resource needs)


What Impacts Fertility Rates/Birth Rates, & Population Growth?

Some factors that might have a strong impact on fertility rates (and population growth or overpopulation) might include:

– High death rates generally mean higher birth rates in a region (parents who know their children will survive have few children)] ( Deaths rates can be impacted by factors such as sanitation, child immunizations, and accessibility and advances in medicine (

– Poverty

– Access to education (and lack of access)

– Social and cultural factors and norms (which can change over time with changes in social, technological and environmental conditions), and religion and ideologies

– Access to birth control and contraception


When poverty rates drop, birthrates soon follow … [and there is evidence of this link in the past few decades in places like Guatemala, Cambodia and Namibia]

– USAID, via


The most overpopulated cities tend to be in developing countries where poverty is rampant due to overcrowding



There is a strong correlation between overpopulation and poverty

… the invention of the birth control pill and other modern methods of contraception resulted in a dramatic decline in the number of children per household in all but the very poorest countries.



[In Afghanistan] Religious and ideological opposition to birth control has been cited as a factor contributing to overpopulation and poverty [and it’s also impacted women’s rights and freedoms]



What Caused Major Jumps In Human Population Throughout History?

Essentially, factors like advances in technology, health, production (and economic growth), standard of living, and more advanced systems.


[Historically] technological revolutions [like the tool making, agricultural and industrial revolutions] have coincided with population expansion.

[These revolutions did things like allow humans to produce more, or get more access to more resources like food]

[As health treatment and medicine advanced, more children were able to reach adulthood now too – which has lead to greater population sizes]



Effects Of Human Overpopulation

Effects On Environment & Resources

Overpopulation can mean more resources are needed by a population as a whole (more consumption of food, water, natural resources, etc.), but also more waste is produced, and there is more pollution and environmental degradation as a flow on result (air, water, and land pollution)

Some issues created (in part by), or exacerbated by an increase in population are:

Waste Pollution (including Plastic Pollution)

Water Pollution

Water Quantity & Quality Related Issues

Climate Change & Increased GHG Gas Emissions

Outdoor Air Pollution

Indoor Air Pollution

Increased Deforestation (with one of the main causes being to clear land for agriculture)

Increased Land & Soil Degradation

Decreased Biodiversity (as a result of habitat loss) – it is thought growth of human population has had more impact on biodiversity than any other single factor in the 20th century – further outlines the impact of an increasing population on wildlife and biodiversity

Food Waste & Loss

… and other issues


The effects of overpopulation can be compounded by overconsumption [where essentially wealthier countries can use more resources and degrade the environment and ecosystems at a faster rate] (


Effects On Humans Health

[Overpopulation can lead to the] … spread of antibiotic resistant bacteria diseases … new viruses that infect humans [from activities like industrial agriculture] … Increased chance of the emergence of new epidemics and pandemics … [and] overcrowded living conditions [are one of the reasons] the poor are more likely to be exposed to infectious diseases (

Environmental problems made worse by overpopulation can lead to human health problems – air pollution is one example of this

In overpopulated areas, slums and crime areas can grow, leading to more risk and lack of safety for people in those areas (due to violence, illegal activity, drugs, and so on)


Effects On Economy

There are too many people trying to fill a limited number of jobs within an area

[When there is too much competition for jobs, labor price is diminished, and unemployment may rise]



Where rapid population growth far outpaces economic development, countries will have a difficult time investing in the human capital needed to secure the well-being of its people and to stimulate further economic growth.

This issue is especially acute for the least developed countries, many of which are facing a doubling, or even a tripling of their populations by 2050.

– UN Population Fund, via


Effects On Geological Epoch

… overpopulation [as well as increased consumption rates and wider use of advanced technology] has pushed the planet into a new geological epoch known as the Anthropocene (


Human Overpopulation Solutions & Strategies

Some of the major ways to address human overpopulation might be:

– Apply solutions on different levels – individual, city, State, country, global


– Collect more data on, and have studies on the total population a specific geographic area (like a city) can sustainably support.

Use this data and these studies to form solutions, and track progress


– Focussing on improving overall quality of life, or standard of life, to a particular benchmark e.g. access to healthcare, or cleanliness of cities


– Reduce poverty (in part – this involves investment, growing and diversifying the economy, creating new jobs, and helping economies and businesses become self sufficient without the need for aid or ongoing support)


– Increase the level and availability of education. outlines this :’In order to combat poverty [and help ensure children are surviving into adulthood] in the most overpopulated cities, education and economic growth are critical [and this will also help overcome] environmental pollution

From ‘Educating girls reduces birthrates, as well as women enter the workforce, starting businesses, inheriting assets and otherwise interacting with men on an equal footing, their desire for more than a couple of children fades even more dramatically.’


– Increase access to quality healthcare and overall health – especially for young children in regions where child and teen death rates are higher. outlines the importance of this too: ‘Addressing global poverty and keeping children alive is crucial for reducing overpopulation’.

Bill Gates (via mentioned something similar: ‘The key thing you can do to reduce population growth is actually improve health’


– Have safe, and effective contraception and birth control widely available. Some also suggest having safe abortion available as a backup. indicates: ‘Worldwide, nearly 40% of pregnancies are unintended (some 80 million unintended pregnancies each year … In poorer countries, women have unplanned pregnancies, and might like to be able to space out their pregnancies more.’

From ‘In every nation … in which a choice of contraceptives is available and is backed up by reasonably accessible safe abortion for when contraception fails, women have two or fewer children.


– More awareness on family planning


‘Most of the drop in Chinese fertility occurred … as the government brought women by the millions into farm and industry collectives and provided them with the family planning they needed to stay on the job.’

‘Many developing countries—from Thailand and Colombia to Iran—have experienced comparable declines in family size by getting better family-planning services and educational opportunities to more women and girls in more places.’


– Consider the role of women in population growth.

From ‘Where women [are put in control of their reproductive rights] birth rates fall. [Female education and women in the work force can also help]’


– Track important statistics that are strongly linked to population growth – like fertility rates, adult and child mortality/death rates, immigration rates, etc


– Keep track of environmental boundaries, and how close we are to crossing them to the point that it’s difficult, or impossible to restore the environment to a sustainable condition (or reverse environmental damage)


– Separate to population totals, look at other factors such as how much and how efficiently we consume, increasing the availability of renewable natural resources (like water from desalination), etc.


– Consider the impact of better city and urban planning on society and the ability to meet the needs of the society.

From ‘… urbanization may be the best compromise in the face of global population growth … [and it might happen if] urban planning is significantly improved and city services are properly maintained.’


– It’s possible that changes in lifestyle (such as choice of diet as one example), changes in resource generation technology, and other factors, could support further sustainable population growth. suggests something similar to this: ‘Changes in lifestyle could reverse overpopulated status without a large population reduction’


– Consider the impact of social, cultural, behavioral and political norms on fertility rates, population growth, and overpopulation.

As just one example, cultural and religious beliefs of community members in a country can influence birth rates


– Consider the impact of government policies and laws on number of children people are having.

One example is the China one child policy.

Another example is the forced sterilization that has been tried in countries such as India before.

One idea, per, that has been floated is: ‘[Choice-based, marketable birth license plans are also an option] where the market would determine what the license fee for each additional child would cost [beyond a certain pre determined population growth goal]’


– Consider the viability of space expansion to cater for society’s needs.

From ‘Space Expansion … Extraterrestrial settlement & space colonisation is also a potential solution to explore. [Some sources indicate the] resources of the solar system could support 10 quadrillion (1016) people. But, other sources argue it is not viable to address Earth overpopulation by expanding to Space’


– What is worth pointing out from a solutions point of view is that at some point, technology and science can only do so much to address overpopulation.

At some point, the behavior and thoughts of humans and society has to be the thing that changes. outlines this:

Scientists and technologists … caution that science and technology, as currently practiced, cannot solve the serious problems global human society faces, and that a cultural-social-political shift is needed to reorient science and technology in a more socially responsible and environmentally sustainable direction


Top 20 Countries With Largest Populations In Total People

As of September 2018, the top 20 largest population countries were:

1. China – 1,416,221,148

2. India –  1,357,226,853

The USA was in third at 327,258,161

In order from 4th to 20th – Indonesia, Brazil, Pakistan, Nigeria, Bangladesh, Russia, Mexico, Japan, Ethiopia, Philippines, Egypt, Vietnam, Democratic Republic Of The Congo, Germany, Iran, Turkey, and Thailand.



In addition to countries, we might also look at the cities with the largest populations, and match them up with cities with the lowest average incomes, and lowest quality of life.


Stats Relevant to Population Size Now, & Population Sizes Forecast For The Future (by 2050 and 2100)

You might like to look up stats relevant to:

– Total population size

– The growth rate of a population (how quickly it’s growing per year)

– Future projections of population growth and size, by 2050 and 2100


Some relevant stats are …


Future Forecasts

The world’s population will rise from just over 7 billion in 2012 to nearly 9.6 billion by 2050 (

The world population is currently growing by approximately 74 million people per year … [and] the world population will reach 9.0 billion around 2050, assuming a decrease in average fertility rate from 2.5 down to 2.0 (


Where Population Growth Will Take Place

Almost all growth will take place in the less developed regions, where today’s 5.3 billion population of underdeveloped countries is expected to increase to 7.8 billion in 2050 (


[some of] the least developed countries … are facing a doubling, or even a tripling of their populations by 2050 (UN Population Fund, via


Developed Regions Will Stay Stable/Unchanged

… the population of the more developed regions will remain mostly unchanged, at 1.2 billion (


United States Future Population Forecast

An exception is the United States population, which is expected to increase by 44% from 2008 to 2050 (


Birth Rates vs Total Fertility Rates & Replacement Rates

There’s a difference between birth rates, total fertility rates, and replacement rates.


A general description of each might be:

– Birth Rates

… the number of live births per 1,000 women in the total population (


– Total Fertility Rates

“Replacement level fertility” is the total fertility rate—the average number of children born per woman—at which a population exactly replaces itself from one generation to the next, without migration. (


– Replacement Rates

If, on average, women give birth to 2.1 children and these children survive to the age of 15, any given woman will have replaced herself and her partner upon death. A TFR of 2.1 is known as the replacement rate (


What Are The Birth Rates & Fertility Rates In Different Countries & Regions Right Now?

The birth rates by country development level are:

World – 2.5

More Developed – 1.7

Less Developed – 2.6

Least Developed – 4.3

– UNFPA, via


Where Will Population Growth Take Place In The Future?

Sub-Saharan Africa … [had a] total fertility rate [of] 5.4 during the 2005–10 period― double that of any other region―and is projected to decline only to 3.2 by 2050 … These expected reductions in fertility rates reflect expectations of increasing urbanization, expected declines in child mortality, and increases in income, among other factors (


An interesting stat on the future of population growth in low income countries is:

The UN projects the population of the 48 poorest countries in the world will double from 850 million in 2010 to 1.7 billion in 2050 (Population Institute, via the


There is also a list of the fastest growing cities in the world at


Carrying Capacity Of Earth, & Different Regions On Earth

We’ve written different guides on carrying capacity:

What Is The Carrying Capacity Of Earth Now, & In The Future?

Which Type Of Food Diet Can Support/Feed The Most People In Society? (Food Carrying Capacity)


An estimate of the carrying capacity of Earth according to one source:

A world population of around a billion would have an overall pro-life effect.

This could be supported for many millennia and sustain many more human lives in the long term compared with our current uncontrolled growth and prospect of sudden collapse 



Factors Other Than Population Size & Growth To Look At When Analysing Overpopulation As An Issue

Beyond looking at overall population numbers, there’s other indicators that can be assessed in order to determine when a region might be suffering from overpopulation. 

These factors might include, but aren’t limited to:

– Resource scarcity levels (such as how much available fresh water for drinking and other uses it has)

– Quality of life indicators (such as homelessness and access to certain basic services like health care, or how overcrowded a city is)

– Human health indicators

– Wildlife, biodiversity, environmental and ecosystem indicators

– Economic factors might include things like unemployment levels, and income levels.

These things can be indicators and benchmarks of how sustainable or unsustainable a population size is.


Also, we might look at factors such as human density – which is the number of people per square mile in that city.

The more people per square mile, the more overcrowded a region might be.


10 of the most overcrowded cities in the world in 2017 based on number of people per square mile are:

1. Dhaka, Bangladesh – 16,235,000 total people, and 114,300 per square mile

2. Hyderabad, Pakistan – 2,990,000 total people, and 106,800 per square mile

3. Vijayawada, India – 1,775,000 total people, and 80,700 per square mile

4. Chittagong, Bangladesh –  3,250,000 total people, and 75,600 per square mile

5. Mumbai, India – 22,885,000 total people, and 67,300 per square mile

The other 5 in order from 6 to 10, are Hong Kong, Aligarh in India, Macau, Hama in Syria, and Mogadishu, Somalia (Mogadishu is at 64,700 per square mile)



Overpopulation vs Systemic Problems

It’s possible to look at a population and diagnose the cause of one of their problems as being from overpopulation.

However, sometimes it’s less from overpopulation, and more from systemic problems.


One example of this is starvation:

Today, starvation is caused by economic and political forces rather than a lack of the means to produce food (












10. – most populous cities by 2100








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