Human Overpopulation: Causes, Effects, Problems & Solutions

Human overpopulation is an issue in it’s own right.

But, it’s also an issue that contributes to other key environmental and social issues.

The logic behind this is that more people generally means more consumption of resources (of food, water, natural resources etc.), and more consumption can lead to more waste generated, more pollution, and other issues stemming from increased demand, production and consumption.

In this guide, we discuss the causes, effects, problems and potential solutions relating to human overpopulation.


(Note – this guide includes general information on human overpopulation, and is more of a ‘starter’s guide’ on the issue rather than definitive guide for the issue of overpopulation)


Summary – Human Overpopulation

Human Overpopulation vs Population Growth

There is a difference between these two things

We outline the different in the guide below


What Is Human Overpopulation?

Human overpopulation is generally reached when the population in a specific area exceeds the carrying capacity of that area

Some of the signs of overpopulation might be the depletion or lack of non renewable resources, and degradation of the environment

Loss of quality of life might be one example of a side effect of human overpopulation in an area

There is a difference between supporting a population’s basic needs, and supporting all consumer choices – which might be excessive, and/or unsustainable. This is an important delineation to make when talking about overpopulation or carrying capacities


Is Human Overpopulation Different To Overcrowding?

These two phrases might refer to different things.

We’ve outlined what the different between human overpopulation and overcrowding might be in the guide below.


Current Size Of The World Population

The current world population size is close to 8 billion people

China and India by far have the largest populations of all countries

Less developed and least developed countries currently have far higher birth rates than more developed countries 


World Population Size Forecasts For The Future

By the year 2050, the world population size could reach between 9 billion to 9.74 billion people, according to different forecasts

By the year 2100, the world population size could reach between 10.9 to 11.2 billion people, according to different forecasts

Population size in the future is influenced by average fertility rates

Several sources indicate that almost all global population growth in the future will occur in African countries (and to a lesser extent Southern Asian countries), and the least developed or poorest countries int he world. Some of the least developed countries are facing a doubling or tripling of population size

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.

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.

Developed countries are expected to remain mostly stable with their population sizes at 1.2 billion, with one exception being the US, who could see a 44% increase in population from 2008 to 2050 according to

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.


What Caused Large Increases In Human Population Sizes Throughout History?

We list some of these causes in the guide below, but, factors like advances in technology, health and medicine, production, economic growth, standard of living, and improved systems and practices contributed to large increases in human population sizes throughout history.


Causes Of Human Overpopulation

Causes of human overpopulation might be split up into population side factors, environment and resource side factors, and economic and social side factors.

We’ve listed these factors in the guide below


Factors That Might Impact Fertility Rates & Birth Rates

In the guide below, we list the factors that might impact fertility rates and birth rates

They include but aren’t limited to high death rates in a region, poverty, access to education, social and cultural factors and norms, and access to birth control and contraception


Effects Of Human Overpopulation

Effects of human overpopulation can span across the environmental and depletion of natural (and non renewable) resources, human health and safety, the economy, and other miscellaneous areas of society

We list different individual effects in the guide below

It’s worth noting that the effects of overpopulation can be compounded by overconsumption, ineffective or inefficient social and governmental systems, ineffective technology, environmental pollution and degradation, and other factors


How Human Overpopulation Might Be Managed – Potential Solutions & Strategies

We outline some potential solutions and strategies in the guide below


Birth Rates vs Total Fertility Rates & Replacement Rates – The Difference

We outline the difference between what each of these terms means below in this guide.


Population Size vs Systemic Problems

Whilst population growth can impact issues that arise from overpopulation, some issues are cause by problems with the systems that are set up in society, and not necessarily the size of the population in any one area.

We give an example of this in the guide below.


Other Notes

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 

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

Even in developed countries and cities, there can be supply issues related to population. Perth in Western Australia for example 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.

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 

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?’


Human Overpopulation vs Population Growth

Human overpopulation is different to population growth.

Population growth is simply an increase in the number of people within a population without taking into account the effects of that increase on specific factors like the environment and resources.

Human overpopulation on the other hand does take into account those effects.

Population growth is usually part of the broader issue of human overpopulation.


What Is Human Overpopulation?

Human overpopulation specifically involves:

– … the ecological footprint of a human population (which takes into account resource production, resource consumption and the ability to deal with waste generated from production and consumption) in a specific geographical location exceeding the carrying capacity of that location

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

One example of degradation might be when planetary boundaries are crossed or exceeded


So, it relates specifically to how a geographical area can provide adequate resources (including natural resources from the environment) 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.

Resources might be depleted in a specific area, but access to resources might be gained via importing resources from other States, Provinces or countries.

It’s also possible new technology and new processes/practices might open up avenues to increase the availability of resources.

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

Loss of quality of life may be one example of a side effect of human overpopulation.


Is Human Overpopulation Different To Overcrowding?

These terms can mean similar things, or different things, depending on who is using them.

If there is a difference …

– Human overpopulation might refer to the population not being able to be sustained by the available resources and environment

– Whereas, overcrowding may refer to the population size reaching a point in a specific location/space where health and safety are at risk, or living becomes uncomfortable.


What Is The Current World Population Size?

World Population Size

In 2020, the world population was close to 7.8 billion people (


Countries With The Biggest Populations

Obviously though, the population in each country around the world differs significantly.

China and India by far have the largest population sizes of all countries right now.


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.]



Cities With Largest Populations

In addition to countries, it’s also possible to look at the cities with the largest populations.

Matching up the most populated cities with things like consumption rates can give an idea of the cities that are the largest consumer cities in the world


Countries With The Highest Birth Rates

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


World Population Size Forecasts For The Future – By 2050 and 2100

According the the forecasts below, most of future population growth worldwide will occur in Africa, or the least developed and poorest countries in the world.

The US is expected to increase it’s population size close to 45% by the year 2050, but appears to be the exception in population size growth amongst developed countries.


By Year 2050

[The population by 2050 is expected to reach around 9.74 billion people] (


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 (


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


By Year 2100

By 2100, the world’s population is projected to reach approximately 10.9 billion



The UN projects that the global population increases from a population of 7.7 billion in 2019 to 11.2 billion by the end of the century.

By that time, the UN projects, fast global population growth will come to an end



Which Geographic Regions Future Population Growth Is Forecast To Take Place In

About two thirds of the predicted growth in population between 2020 and 2050 will take place in Africa (


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 (


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 (


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

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


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


Developed Regions Expected To 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 [to developed countries staying unchanged/stable] is the United States population, which is expected to increase by 44% from 2008 to 2050 (


What Caused Major Increases In Human Population Sizes Throughout History?

Essentially, factors like advances in technology, health and medicine, production (and economic growth), standard of living, and more advanced or improved systems and practices contributed to large jumps in population size throughout human history.


[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]



Causes of Human Overpopulation

There can be a range of factors that lead to human overpopulation.

These factors might be split up into population side factors, and resource and environment side factors. 


Some of the causes of human overpopulation in a particular region might include but aren’t limited to:


Population Side Factors

– A higher birth rate or fertility rate

– A decline in the mortality rate

– An increase in immigration


Environment & Resource Side Factors

– Degradation of the natural environment by humans, and, the inability to reverse some forms of environmental degradation once they’ve happened

– Depletion of natural and non renewable resources by humans by overconsumption, misuse or mismanagement 

– Not being able to generate or get access to new resources to meet demand of the population (whether that involves local production of resources, or importing resources)

– A local environment that is naturally unsuitable for human population of certain sizes because of factors such as a very dry climate, poor soil or land, a lack of natural resources, or poor access to natural resources. In this instance, the natural conditions are a bigger problem than the management of resources and the environment by humans


Social & Economic

There can also be a range of social and economic factors that contribute to human overpopulation

We list some of these in the fertility rates and birth rates section below


What Factors Might Impact Fertility Rates & Birth Rates?

Some factors that might have a strong impact on fertility rates and birth rates might be:

– High death rates in a region

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

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 (


– Access to education (and lack of access)

Several sources cite education as a factor that impacts birth rates in different regions


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

[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] (


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


– Access to birth control and contraception

… 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 (


Effects Of Human Overpopulation

The effects of human overpopulation may span across the environment and natural resources, human health, the economy, and other miscellaneous areas.

Those effects may include but aren’t limited to …


Effects On Environment & Natural Resources

A greater population size can mean more demand, which can mean:

– More resources are needed in general by the population (food, water, natural resources)

– More production and consumption of resources, which can mean more waste, pollution (air, water, and land pollution) and other environmental issues and side effects. 


Some environmental and resource depletion issues that a growing population can contribute to can include but aren’t limited to:

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

How Much Resources We Have Left On Earth, & Whether We Will Run Out Of Resources In The Future

Food Waste & Loss

People Currently Experiencing Chronic Hunger & Malnourishment Issues, & Total Number Of People Experiencing These Issues Potentially Growing In The Future As The Population Grows Worldwide

Increased Pressure On, & Resources Invested In Food Production & Agriculture In The Future As A Result Of More Food Demand

Issues related to environmental planetary boundaries, ecological footprints, and the carrying capacity of Earth

… 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 Human 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 (


It’s also possible that environmental problems made worse by overpopulation, such as air pollution as one example, can lead to some human health risks or issues

It’s also possible that overpopulated or overcrowded areas can turn into slums or areas where crime and other unsafe behaviour (like violence, illegal activity, drugs, and so on) can take place, leading to more risk and lack of safety for people in those areas


Effects On Economy

On one hand, more people coming into a population introduces more skills and labor to an economy for businesses to choose from, but, there can also be downsides.


Too many people trying to fill a limited number of jobs within an area [leads to a level of job competition where 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


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


Effects On Geological Epochs

… 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 (How Overpopulation Might Be Managed)

There might be a number of potential ways to manage human overpopulation, or to try to address the issues that human overpopulation causes.

Some of the potential ways to manage human overpopulation might include:

– Understanding that human overpopulation might be an issue best focussed on at the city level, town level, and the areas where majority of people inhabit 


– A better understanding by city governments and city decision makers on the maximum number of people a city can support, according to access to resources, rates of environmental degradation, and other factors relevant to human overpopulation

There may need to be more data collection and studies on the total population a specific geographic area (like a city) can sustainably support as part of this

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.

This data might be used to influence future decisions made by governments


Going further into indicators that might be kept track of:

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 according to 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)


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 though, heavily populated cities might deal with intense smog and pollution problems that exacerbate health and poverty issues.


– Implementation of solutions by cities and countries that are considered to be experiencing human overpopulation

In practice, this could involve a complex and multi faceted strategy

With international trade, consumer cities can import resources, and outsource environmental degradation to producer cities

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

Countries and cities that over consume may need to change their habits to be more sustainable, and this may be a start for addressing things such as resource depletion and environmental degradation that are core to human overpopulation suggests something similar to this: ‘Changes in lifestyle could reverse overpopulated status without a large population reduction’

There may be other solutions that may need to be implemented too though

Two examples might be advances in technology, and better city and urban planning:


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.’


An example of advances in technology to increase resource capacity might include the construction and operation of desalination plants. Although, they do come with drawbacks and tradeoffs.


– Managing and capping fertility rates and birth rates in regions with unsustainable fertility and birth rates

This might also involve a complex and multi faceted strategy

Factors like poverty, access to effective and safe contraception and birth control (some also suggest access to safe abortions), access to education in general, access to more education on family planning, awareness of how social, cultural, behavioral and political norms and expectations may be impacting overpopulation, and other factors would all have to be addressed in countries experiencing the highest population growth


On poverty:

To use one example, poverty can be difficult to address in countries with a weak overall economy, and without the political foundation to grow and stabilise an economy 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.’


On poverty again:

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


On contraception and birth control: 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.


On more awareness of family planning (from

‘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.’


Other birth control methods:

One example of implementation of solutions via government policy 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]’


– 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’


– 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]’


– 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’


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


Birth Rates vs Total Fertility Rates & Replacement Rates – What’s The Difference?

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

It’s worth noting that the total fertility rate and replacement rate is the same thing.


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 (


Population Size 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









19. Max Roser (2020) – “Future Population Growth”. Published online at Retrieved from: ‘’ [Online Resource]



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