Population and environment – what's the connection?

This topic is sponsored by the Australian Academy of Science's Population and Environment Fund.

Key text

A complex problem

While the global and local list of environmental problems is long and growing, it's difficult to be certain of the extent to which population growth is a contributing factor. For example, land degradation in Australia is a major concern. Rabbits are a major cause of land degradation in some regions of the country, yet they were introduced to the country by just one person. This is a problem of too many rabbits, not too many people.

Clearly, the relationship between the environment and population is complex. To explore it further, we need first to look at population growth.

Population growth in Australia

Nobody knows how many indigenous people lived here before European settlement: estimates range between 300,000 and 1.5 million. It is known, however, that their numbers declined significantly after the arrival of the First Fleet in 1788.

Related site: AusStats: Population clock Up to the minute projection of Australia's resident population. (Australian Bureau of Statistics)

By 1887 there were probably about 3 million people, of mostly European origin, living in the colonies. Australian Bureau of Statistics figures show that the 1901 census counted 3,773,801 people. One hundred years later, in 2001, the national census tallied 18,972,350 people. The estimated Australian population mid-2004 was 20,111,300.

The human population keeps growing

The human population at the global level has been growing exponentially over time (Box 2: Exponential growth). The absolute number of humans has continued to increase, and the distribution of the population has changed, due to differing birth and death rates and the movement of people from one region to another.

Australia's population also continues to increase. The three factors which have the greatest impact on the population of any nation are birth rate (fertility), international migration and death rate (mortality rate).

The total fertility rate (TFR) is the average number of children a woman gives birth to in her lifetime. A TFR of 2.1 is considered to be the replacement rate, which is the fertility rate needed to keep the population stable if there is no net migration. Australia's TFR in 2000 was 1.7. Most developed countries have TFRs below the replacement rate. The 2004 estimate of the world average TFR is 2.8, ranging from 1.2 to 8.

Immigration adds to the Australian population in two ways: firstly, the immigrants themselves; and secondly, their Australian-born children (Box 3: Immigration and population growth). The contribution of net overseas migration to Australia's population growth has averaged about 39 per cent for the past 25 years. This is projected to increase as the Australian fertility rate decreases.

The age structure of a population can also contribute to its growth. A population with a large percentage of people in the child-bearing years (15-45) will continue to increase even if parents do not produce enough children to replace themselves. This is because there are a lot of young people yet to have children and a low number of old people who will die in the next few decades.

Related site: Australian social trends – population Fertility, death rate and migration influence the size and structure of Australia's future population. (Australian Bureau of Statistics)

The combination of birth rate, migration and death rate affects both population size and the age profile. Australia's population is steadily ageing. Over the next few decades in Australia, the number of people over 65 years of age is predicted to increase, and children will make up a smaller proportion of the population. Population ageing is mostly due to falling fertility rates and increasing life expectancy. An ageing Australian population has economic and social consequences.

Our consuming passion

Although some aspects of the Australian environment are in relatively good condition, Australia has many environmental problems: land degradation, endangered species, an increasing incidence of toxic algal blooms in our rivers, declining fish stocks, land clearing, air pollution, and vulnerable water supplies. There are more, but that will do for a start.

Many environmental problems can be attributed to poor management techniques, policy failure or even feral animals. Such factors are largely independent of population, but the sheer number of people can also contribute to the problems.

Consider, for example, the issue of consumption of material resources. On average, Australians have become steadily richer over the last few decades. As monetary wealth has increased, so has consumption. As a nation we now own more goods, use more energy, eat more processed food and have larger houses than ever before. All this consumption can create environmental problems. In effect, the populated areas of Australia are a sink for natural resources, draining the continent of nutrients, minerals and water. What we don’t consume we export, generating revenue which we use to buy consumer items from abroad. High levels of consumption help to deplete our store of resources, generate waste and increase the stress on the natural and agricultural environments.

The environmental impact of copious consumption may not be confined to the local area. For example, the use of fossil fuels for energy in Australia can have an impact on global carbon dioxide levels and resulting environmental effects.

When Australian consumption is viewed from a global perspective, we leave a large 'ecological footprint'. The ecological footprint is a measure of how much productive land and water is needed to produce the resources that are consumed and absorb the wastes produced by a person or group of people. In 2001, there were 1.8 hectares of globally productive land per person. In 2004 Australia's ecological footprint was calculated at 7.7 hectares per person (among the world's top four resource-consuming nations) compared to the average global footprint of 2.2 hectares. Clearly, the consumption of resources at current levels is not sustainable.

The limits to growth

Some economists have described humans as the 'ultimate resource', because they can turn previously useless things into resources by being intelligent, adaptable and creative. Much of what we value and what makes life enjoyable is the product of human endeavour. However, something good can become a problem when in excess – when there is 'too much of a good thing'.

Factors such as population growth, population distribution and migration combine with high-consumption patterns to put stresses on the environment. There is a limit to the environment in terms of supply of resources and the ability to absorb waste products. Examples include the rate of tree growth for timber harvesting, the available fresh water for irrigation and human consumption, and the time required for the recycling of organic waste. Land degradation, loss of forest cover, pollution of water and air, soil erosion and loss of biodiversity are all occurring at a fast pace, and are evidence of the impact of an increasing population on the environment.

Population and the environment

The maximum number of a particular organism that an environment can maintain indefinitely is often referred to as its carrying capacity. How do we calculate the human carrying capacity of the Earth? We can't do it by numbers alone because the relationship between population and environment is neither simple nor straightforward.

To come up with the best solution, insights and ideas need to be drawn from many disciplines. These include, but are not limited to, environmental science, geology, economics, demography, human biology and health, geography and political science. The future of both the global human population and the global environment relies on bridging disciplinary divides.

Related Nova topics:

Australia's threatened species

Cleaner production – a solution to pollution?

Feeding the future – sustainable agriculture

Box 1: Trends in world population

From 1994-2004, the world population grew at a rate of about 1.3 per cent per year. This is down from 1.7 per cent in the 1970s and 1980s but the lower rate is applied to a much larger population. Population growth varies geographically across the globe with rates of 0.3 per cent in more developed countries compared with 1.6 per cent in countries that are less developed. Australia's current growth rate, including immigration, is 1.2 per cent.

Population size is influenced by the birth rate and the death rate

The two main factors that influence the size of the world's population are the birth rate (or fertility) and the death rate (or mortality). The main reason the world's population has increased so dramatically in recent centuries is because the mortality rate has declined. People live longer due to improvements in hygiene, nutrition and medicine. Importantly, a much higher proportion of infants survive the rigours of early childhood.

Because mortality has declined more rapidly than fertility, the world's population is increasing. Developed countries, including Australia, the United States, Japan and some European nations, have recently seen dramatic declines in fertility to a point where the natural increase in population (ie, excluding immigration) is virtually zero. They are said to have completed the demographic transition from a high fertility, high mortality population to a low fertility, low mortality one.

However, populations in many developing countries continue to increase. Many of these are about halfway through the demographic transition: mortality has declined significantly, but fertility remains high. Ninety-five per cent of the yearly population increase from 1994-2004 occurred in less developed countries.

The demographic transition gives us hope that the human population will be able to reach stability without disasters in the form of mass starvation or killer diseases. Education, particularly of women, improved living standards and access to contraception are important factors in achieving the transition.

Related sites

• Population growth coming to an end (transcript from PM, 2 Aug 2001, Australian Broadcasting Corporation)

• Human population growth (Biology by J.W. Kimball, USA)

• 2004 World Population data sheet (Population Reference Bureau)

• United Nations Population Information Network (United Nations)

• US and world population clocks (US Census Bureau)

Box 2: Exponential growth

After 40 minutes you would see only four bacteria. Twenty minutes later, there would be just eight. Not much chance of any rapid overcrowding – so you decide to go out and come back the next day. Twenty-four hours later, how many bacteria might you find?

About 1,000,000,000,000,000,000,000,000 (10²⁴), or one million billion billion! Their initial rate of growth (doubling every 20 minutes), although it seems slow at first, is actually frighteningly fast, as you can see on the graph. This growth rate produces a curve with a characteristic shape, sometimes known as a J-curve.

Once the population reaches about 1000 bacteria, which takes ten doublings, or 3 hours and 20 minutes, we start to deal with large numbers and doubling has dramatic results. For example, in just the final 20 minutes of a 24-hour period, the same number of bacteria were created as were made in the previous 23 hours and 40 minutes.

Geometric and arithmetic increase

This sort of growth rate – where the number added depends on how much is already there – is called exponential growth or geometric increase. The same principle applies in the calculation of compound interest, when a sum is deposited in a bank and the interest is reinvested. It is different from arithmetic (or additive) increase, where the same absolute amount is added in each time interval. In exponential growth the same percentage is added each time but, because the percentage is calculated from a growing base, it represents a greater absolute number per unit of time.

Limits to bacterial growth

Of course, in reality, after 24 hours you would only find a test tube of bacteria, their food run out and many of them dead. Fortunately for us, and for everything else in the world, bacteria can’t keep up their maximum growth rate for long. It can only happen under the best of circumstances (what scientists call the optimal environment). Think of the factors that act to limit the growth of bacteria. Obviously, food starts running out, waste accumulates, and so the reproductive rate of the bacteria falls. For example, suppose poor conditions mean that a quarter of the bacteria die during the course of each 20 minutes (the doubling time). Is the population still growing exponentially? The answer is yes – even though it is not at the fastest rate of growth that the bacteria are capable of. The population will take longer to double, but the shape of the J-curve remains much the same.

Human population growth

The story of the human population is similar in some respects to the bacteria in the test tube. We are, for the foreseeable future, confined to a large test tube – the Earth – where we find the conditions necessary for our survival. The human population is currently doubling every 53 years. That is much more slowly than the bacteria, but unless something changes, it is still only a matter of time before we could find ourselves in the same situation – resources running out, waste products accumulating, and a high death rate.

Related sites

• Eliminating the zeroes (Box 1 of Nova topic, Harnessing direct solar energy)

• Modelling exponential growth – using logarithms (Department of Mathematics and Statistics, University of Saskatchewan, Canada)

Box 3: Immigration and population growth

However, some people have used economic factors to argue against big population increases for Australia. We still largely make our way in the world by exporting minerals, along with fibre and food. They argue that, unless our level of domestic consumption falls drastically, a much larger population would mean less meat, cereals or other foodstuffs to export. (The domestic consumption of fibre and minerals would still remain very low compared with the proportion exported.) Economists reject such a view because it assumes that there is a fixed level of production, when experience shows instead that output is quite responsive to growth in demand.

Environmental scientists point out that Australia is already suffering considerable damage to its soils, waterways, coastal zones and natural habitats through intensive agriculture, urban expansion, industrial development and the ever-increasing demand for goods and services. Groups who oppose population increase on environmental grounds suggest that even the present Australian population cannot be indefinitely sustained at its present rate of consumption by the renewable resources of the continent.

Those who hold this view are sometimes criticised for being against migrants. Whatever the validity of the idea of no further population growth, being against continued immigration does not necessarily mean being against migrants already here. Each migrant who comes to Australia is of value and contributes to our society. This is also true of each new baby born, but in itself it is not a reason for increasing the birth rate. Of course, immigration to Australia does not increase the global population problem in the way that births do; and it certainly eases the plight of those individuals who may settle here from countries where the standard of living and opportunities for a full life are less than our own. It also eases environmental pressure in the home countries of migrants.

More recently, there is a growing trend for Australians to leave the country, either long-term or indefinitely. Those people leaving tend to be younger and more educated than the general population, leading to the expression 'brain drain'.

International immigration

Some argue on humanitarian grounds that Australia should help by taking people from overcrowded countries. However, the number of migrants that Australia takes does virtually nothing to ease the overpopulation elsewhere in the world. Our net immigration intake of 154,225 in 2002-03 was 0.1 per cent of the 73 million extra people in the world that year.

The scale of international migration has increased in recent years. The annual flow of migrants on a global scale is estimated to be between 5 and 10 million people. The pattern of international migration differs between world regions. The largest immigrations in the mid-1990s were from Latin America and Asia into North America and from Eastern Europe, the countries of the former Soviet Union and North Africa into Northern and Western Europe. There is also a significant movement of people within Asia, Africa and Latin America.

Using immigration in population projections

Demographers can estimate Australia's future population size by using different levels of net immigration (ie, the total number of people settling permanently in Australia minus the total number of people leaving Australia permanently).

For example, if the net immigration figure each year is 100,000 then Australia's population will be 26.4 million by 2051. If immigration had ceased in 2002, then Australia's population would decline to 19.8 million by 2051. (These predictions are based on the assumption of below replacement fertility among the resident population. This is when the number of babies being born is less than that required to replace the parents.)

Other population pressures on our environment

Population pressures on our environment come not only from a resident population, they also come from

• a global population, where there is demand for Australian-based production;

• overseas visitors to Australia, especially tourists but also business visitors, students and guest-workers. These numbers are many times that of immigrants.

Related sites

• Fact sheet index (Department of Immigration and Multicultural and Indigenous Affairs, Australia)

• Leaving Australia: A new paradigm of international migration (Parliament of Australia, Parliamentary Library)

• Human population – fundamentals of growth: Effect of migration on population growth (Population Reference Bureau, USA)

• World migration 2003: Managing migration – challenges and responses for people on the move (International Organization for Migration)

Activities

• Australian Bureau of Statistics
  • Census profile activities – population trends – five lessons in which students retrieve and analyse population data from the 2001 Australian Census and look for trends in population in states and territories. Lessons are available as PDF files.
  • Population estimates and projections – students learn about the mathematical processes involved in estimating the size of the Australian population based on census results.

• Environmental Protection Agency, Victoria (Australia)
  • Ecological footprint – students survey different environments and use the eco-footprint calculators for households, offices and schools. The on-line calculators use Microsoft Excel spreadsheets.

• Science upd8 (UK)
  You will need to register to access activities but they are free.
  • Carbon control – students get to calculate their carbon footprints and discuss ways to make their footprints smaller.

• Columbia University (USA)
  • The tragedy of the commons – introduces students to the concept of the tragedy of the commons and helps them understand how we as a society can put a stop to this tragedy.

• University of Arizona (USA)
  • Great gravidity – students use their knowledge of population ecology to think about the impact of the human population on the Earth's ecosystem.

• Actionbioscience.org (USA)
  • Our population and its impact on the planet – contains numerous ideas for class discussion and extension projects based on an article covering the consequences of a rising population on quality of life. The lesson is based on the article Population and the environment: The global challenge.

• Population Reference Bureau (USA)
  • Adventures on Earth – classroom guide of interactive lessons designed to educate students about how people use the environment, the consequences of meeting human needs and the environmental impact of human actions and choices.
  • Human population – fundamentals of growth: Environmental relationships – students look at the relationship between human population and the environment. Teacher's guide is available.

• Educator's Reference Desk (USA)
  • Landscape modifications: Designing man's vision of a global environment – students study local, state, national, and global examples of landscape modification to understand the effects of the changes.

• Population Connection (USA)
  • Food for thought – explores population demographics, land use patterns, energy consumption and distribution of wealth at the global level.
  • Earth: The apple of our eye – demonstrates the limited sources of food available from land and water. Includes discussion questions and suggestions for action.

• Nova (USA)
  • World in the balance – students calculate how long it takes a country's population to double in size and investigate factors affecting population growth rate.

• Science NetLinks (American Association for the Advancement of Science)
  • Population dynamics – students investigate the causes and consequences of population growth and the environmental factors that contribute to it.

Activity 1. Demographic data calculations

1. Calculate the rate of increase of the population (as a percentage per year).

2. Using this figure, find out the predicted doubling time for the population. A mathematical formula exists for this but, put simply, you just divide the rate of increase into 70 for an approximate answer in years.

3. Draw a graph showing the increase in population from 1991 to the year by which it should have doubled. Read off from this your projection for the islands’ population for the year 2000.

4. If you were a demographer advising the country’s government to help it prepare for the future, what would you say in your report? (Refer to the information in the table.)

Solomon Islands population data (1991)
Population (in millions)	0.3
Birth rate (per 1000)	40.0
Death rate (per 1000)	5.0
Total fertility rate (average number of births per woman)	6.2
Population under 15 (%)	47.0
Population over 65 (%)	3.0
Urban population (%)	9.0

Teachers notes

1. Rate of increase: 3.5%
2. Approximate doubling time: 20 years
3. According to these figures, the islands’ population in 2000 should be approximately 0.4 million (The population will have doubled by 2011.)

Activity 2. How many babies are born?

• Calculate how many babies have been born in the last 3 minutes.
• Note that your figure does not represent the increase in the world’s population in that time. Why not?
• What would you need to know to calculate the net increase that occurred in the last three minutes?

Teachers notes

• Just over 890 babies would have been born in the last 3 minutes.
• This doesn't include deaths in the world.
• You would need to know the death rate or deaths per thousand and substract the total number of deaths from the total number of births to calculate the net increase in the world's population.

Activity 3. Aspects of population growth

Early populations

• In what ways were hunter-gatherer populations prevented from increasing too much?
• What effects might the earliest agriculture have had on the immediate environment?
• How might environmental degradation have affected civilisations in the past?

Industrial Revolution

• How do you think the Industrial Revolution has changed our impact on the natural environment and our attitudes to it?
• On balance, do you think that the Industrial Revolution was a good thing for the human race? What about for other species? Explain your answers.

Population increase

• What prevents most organisms from increasing their numbers at their maximum possible rate?
• Why has infant mortality declined so much in the last 100 years?
• What are the consequences of reducing only the death rate in a population?
• If each couple in the reproductive section of a population produces fewer than two children on average, how can such a population still be increasing in size?
• Is putting a compulsory limit on family size the best way to control population growth?

Australia’s population

• What contribution does immigration make to Australia’s population growth?
• Why have ideas about Australia’s optimal population varied so much?
• Explain why Australia has such an uneven population distribution.
• Summarise the arguments for and against continued population growth for Australia.

Environmental impact of population growth

• Summarise the environmental consequences of rapid human population growth.
• Why do some countries use far more resources than others?

Further reading

Useful sites

Report into the condition of the world's population in regard to resource use, poverty and ecological stress. This is part of a larger publication that addresses a wide range of issues to do with global population.
http://www.unfpa.org/swp/2004/english/ch3/index.htm

World resources 2002-2004: Decisions for the Earth: Balance, voice, and power (World Resources Institute, USA)

Emphasizes the importance of good environmental governance and how individuals, government managers, and business owners can make better environmental decisions.
http://governance.wri.org/pubs_pdf.cfm?PubID=3764

AAAS atlas of population and environment (American Society for the Advancement of Science, USA)

• Introduction
  Looks at the consumption of key natural resources around the world.
  http://atlas.aaas.org/index.php?part=2

• Energy
  Looks at the world's growing need for energy.
  http://atlas.aaas.org/index.php?part=2&sec=natres&sub=energy

• Freshwater
  Describes the chronic or acute water shortage in many countries with fast-growing populations.
  http://atlas.aaas.org/index.php?part=2&sec=natres&sub=water

• Foodcrops
  Asks whether the world can feed growing populations.
  http://atlas.aaas.org/index.php?part=2&sec=natres&sub=crops

• Meat and fish
  Describes the implications for land use with the trend towards consumption of meat and fish as countries and families grow richer.
  http://atlas.aaas.org/index.php?part=2&sec=natres&sub=meatfish

• Forest products
  Looks at the challenges the world faces as it tries to find ways of using forests sustainably.
  http://atlas.aaas.org/index.php?part=2&sec=natres&sub=forest

• International trade
  Asks if global markets will take ecological concerns into account in the future.
  http://atlas.aaas.org/index.php?part=2&sec=natres&sub=trade

The population story – so far (World Watch Institute, posted by Sustainable Population Australia) (PDF file)

Article that discusses the impact of a still-rising world population combining with fast-rising resource consumption.
http://www.population.org.au/media/pub/WorldWatch2004.pdf

2004 Fenner Conference on the Environment Understanding the population – environment debate: Bridging disciplinary divides (Australian Academy of Science)

Provides transcripts of talks presented at the two day symposium.
http://www.science.org.au/events/fenner/index.htm

Future dilemmas (CSIRO Sustainable Ecosystems, Australia) (PDF file)

Explores the impact of the size of Australia's future population on our environment, physical economy, national infrastructure and on our quality of life. A summary and guide to the technical report is available as a PDF file at Dilemmas distilled.
http://www.cse.csiro.au/publications/2002/fulldilemmasreport02-01.pdf

How to talk to Americans (Our Planet E-magazine, Earth Action Network, Inc., USA)

Comments on how the public has become insensitive to large scale environmental problems and human catastrophies.
http://www.emagazine.com/view/?2424

Australian Broadcasting Corporation transcripts

• The biology of civilisation (Ockham's Razor, 12 December 2004)
  A discussion of the complex interrelationships between human culture and nature and the idea of ecological sustainability.
  http://www.abc.net.au/rn/science/ockham/stories/s1261472.htm

• Discarding the Bovver boots: Ecological footprints (Earthbeat, 13 April 2002)
  An interview with Professor Bill Rees, the man behind the concept of the ecological footprint.
  http://www.abc.net.au/rn/science/earth/stories/s530081.htm

Ecological footprint (Powerhouse Museum, Australia)

Defines the term ‘ecological footprint’, how it is used and its importance.
http://www.powerhousemuseum.com/pdf/education/teachersnotes/ecologic.pdf

Sydney’s ecological footprint – a size 11 problem? (Online Opinion, Australia)

Uses the concept of an ecological footprint to put a number on a sustainable population size for Australia.
http://www.onlineopinion.com.au/view.asp?article=1189

Ecological footprint quiz (Earthday Network)

Online quiz calculates your ecological footprint.
http://www.earthday.net/footprint/index_reset.asp

World in the Balance population interactives (Nova, USA)

• Human numbers through time
  Looks at population growth over the past two millennia, and what might happen in the next 50 years.
  http://www.pbs.org/wgbh/nova/worldbalance/numbers.html

• Global trends quiz
  Test your understanding of the population trends and environmental challenges facing nations around the world.
  http://www.pbs.org/wgbh/nova/worldbalance/trends.html

• Earth in peril
  Explore how consumption and rapid population growth affect our planet's natural resources.
  http://www.pbs.org/wgbh/nova/worldbalance/earth.html

Glossary

carrying capacity. The maximum number of individuals of a species that can be supported in an area. Carrying capacity is usually limited by components of the environment (eg, food, nesting sites, resources)

demographic transition. The change in a population of an industrialised country that occurs when declines in death rates are followed by declines in birth rates. (A characteristic of non-industrial societies is high birth and death rates.)