We cannot confront the massive challenges of poverty, hunger, disease and environmental destruction unless we address issues of population and reproductive health.
Thoraya Ahmed Obaid, Executive Director, UN Population Fund (UNFPA)

Globally, many experts are concerned that the earth's 'carrying capacity' is already overstrained, and worry that the huge impending increases in consumption in countries such as India and China will add enormously to the burden of greenhouse gases which threaten to heat the planet - not to mention all the other demands which increases in both population and consumption are putting on the earth's natural systems.

Nor is the problem confined to the so-called 'developing world'. The United States, for example, produces a quarter of the world's carbon dioxide emissions with only five per cent of the global population. And, unlike Europe, the US population is growing fast - from 200 million in 1970, to nearly 300 million today and a projected 420 million in 2050.

One of the complicating facts is that much of the world's population - especially in the South - is very young, with plenty of potential to reproduce. So that although the rate of population growth began to decline some 30 years ago, annual additions to the human population are still near to their highest level, with some 77 million being added every year, or over 200,000 people every day. This is equivalent of a San Francisco every week and almost a Germany every year.

These people all need food, housing, jobs and health care. And once basic needs are met, the appetite for other consumer goods and services seems to be limited only by the ability to pay for them. Human impacts on resources and on the environment vary, therefore, not only with changes in population growth and distribution but also with changes in levels of consumption and the technologies involved.

For example, since 1950 the richest fifth of humanity has doubled its consumption of energy, meat, timber, steel and copper per person and quadrupled its car ownership, while the poorest fifth of humanity has increased its general consumption hardly at all.

Making problems worse

For this reason, booming population is only one among many causes of social and environmental problems. But such growth can make these problems much more difficult to solve.

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• Rapid or persistent population growth can force farmers and fishermen to over-exploit fragile ecosystems with damaging results. It can also increase pressures on local infrastructures and services. It speeds the rate of urbanisation (itself not a bad thing), often leading to dangerous, overcrowded and unplanned settlements, with poor sanitation, a lack of clean water and disastrous air pollution.
  

• In some rural settings increased population growth appears to have stimulated new farming methods, but elsewhere it has resulted in the over-use of slash and burn techniques, and unsustainable land clearance on fragile, sloping and forested land and destructive coastal development.
  

• Since 1972, the main driving force leading to pressure on land and water resources has been increasing food production. In 2004, food is needed for some 2.4 billion more people than in 1972. The trend in recent years has shown population growth drawing ahead of food production in some regions of the world, particularly Africa. Some commentators believe that China may soon become a major food importer.
  

• One billion new jobs must be created over the next decade just to maintain current employment levels. The availability of a young, educated labour force can be a bonus in newly industrialising countries, but jobs are especially hard to create in countries with high levels of under-employment, poor educational standards and limited infrastructure - and these are often the ones with rapid increases in population.
  

• Progress in reducing hunger in the developing world has slowed to a crawl and in some regions the number of undernourished people is actually growing. There are still nearly 800 million hungry people in the developing countries - a decrease of just 20 million since 1990-92. To achieve the World Food Summit goal of halving the number undernourished in developing countries by 2015, the average annual decrease required is 24 million - almost 10 times the current level of performance.
  

• According to estimates by Harvard entomologist, Edward O. Wilson, some 27,000 plant, animal and insect species become extinct every year (the vast majority being insects). About 24 per cent (1,130) of mammals and 12 per cent (1,183) of bird species are currently regarded as globally threatened. Most species extinction can be traced to human encroachments on habitat, including forests and coral reefs, which results from population growth and economic development.
  

• Where resources are already limited, rapid population growth can make it more difficult to eradicate poverty, because the economy, infrastructure and the necessary pool of teachers, doctors and other professionals all need to grow faster than supply.
  

• Although the percentage of people in absolute poverty has fallen from 28 to 24.5 per cent in recent years, the increase in population means that the actual number of people in poverty has stayed the same.
  

• More than any other resource, water shortage is becoming critical issue both for agriculture (which makes up about 70 per cent of demand)and industry. A safe water supply is also one of the most important factors in improving the health of poor families. Up to 7 billion people, in 60 countries, will face water scarcity within the next half centrury, according to the UN World Water Development Report released in March 2003.
  

• Human activities have destroyed 11 per cent of the globe's arable land, the size of China and India combined, and over 40 per cent is now degraded in some way. As a result, every year, the world's farmers must feed 77 million more people with 27 billion fewer tons of topsoil.
  

• Population growth is fuelling very rapid urban growth in the developing world. By 2030, nearly 5 billion people (over 60 per cent of the world's population) are expected to live in towns and cities. And while urban settlements have great potential to enrich life, the speed of their growth has led to immense environmental problems. Some 600 million city dwellers are today without adequate shelter and over 400 million do not have access to the simplest latrines.
  

Adolescent girls, India. Credit:Kim Naylor/Christian Aid

Among the many prescriptions for dealing with such problems, perhaps none has such a catalytic effect as the education of girls. This helps lower child and maternal mortality rates; it increases the demand for family planning and reduces average family size (or what the demographers refer to as 'fertility'), it increases the educational attainment by daughters and of their children; it raises productivity; and it improves environmental management.

It is also one key element of the Action Plan agreed at the UN Conference on Population and Development agreed in Cairo in 1994, and further strengthened at follow-up conference in New York in 1999 (for further detail see International Action - Cairo and Beyond).

Additional tables and graphs:

• World Population and Annual Increase, 1950-2000
  

• World Population, 1950-2000, with Projections to 2050
  

• 20 Most Populous Countries Worldwide, 2000
  

• Countries at or Below Replacement Level Fertility, 2000

Sources:

• State of World Population 2003 and 2004 (UNFPA report)
  

• State of World Population 2001 (UN Population Fund report focusing on Population and Environmental Change).
  

• Human Development Report 2003 and 2004, UNDP
  

• UNFPA
  

• World Population Prospects: the 2002 Revision
  

• The State of Food Insecurity in the World 2002
  

• GEO: Global Environment Outlook 3
  

• NOVA: World in the balance
  

• NOVA interactive: Human numbers through time
  

• NOVA interactive: Earth in Peril

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