Because we believe it is unlikely that the UK will be able to support more than 30 million people in the 22nd century. (The reasons are given on this website and detailed calculations appear in the OPT Journal, which use ecological footprinting techniques to establish 'equitable shares' of national environmental demands and impacts on the Earth as a whole.) The most important reason is probably the need for all countries to reduce their share of global greenhouse gas emissions, already causing potentially disastrous climate change. However, even if greenhouse gas emissions stabilise at below life-threatening levels, there will still be a need to adjust to a near exhaustion of affordable fossil fuel supplies by the mid 21st century. The UK is failing to meet its internal emissions targets and on present trends is highly unlikely to have alternative clean energy sources in place in time. Technological change alone cannot solve this problem - populations need to be stabilised and reduced worldwide. Another reasons for these low targets (which can be raised at any time) is the need to be able to be self-sufficient in food (including ocean produce) and to guarantee security of supply, without causing further environmental degradation. Population growth is the multiplier of all environmental problems. On the positive side, imagine the huge improvement in the quality of life that would result. The UK could be twice the country with half its population. OPT's suggested population strategy of stabilisation and gradual reduction (by about 0.25% a year) would not involve coercion on family size, and would achieve an initial target of 52 million in 2050, with continuation if necessary to 30 million by 2121. See our Population Policy Projection A on the OPT Population Policy Projections section.

Not necessarily. If population size were crucial, both India and China would be more economically powerful than the USA. Finland produced one of the world's largest companies - Nokia - and in October 2003 was rated highest for growth prospects by the World Economic Forum Global Competitiveness report. (The USA ranked 50th.) Denmark has the largest wind-turbine manufacturing company in the world. The economies of the US (280 million people) and Japan (127 million people) performed less well than those of many smaller countries in 2002. Successful economic management, high productivity, good business strategy, innovation and specialisation are more important than underlying population size. Where market size demands a big organisation, an international company can be formed. For example, Royal Dutch Shell, which is Anglo-Dutch. Or companies can succeed by being small, clever and a bit lucky - like another oil company, Cairn Energy of the UK.

No. One of the arguments made for increasing population growth and the relative numbers of young people (whether by natural increase or immigration) is that a successful economy needs innovators and entrepreneurs to develop successfully. Even if successful innovation and entrepreneurship is the preserve only of those under 30 (not the case), a lack of business talent in the UK cannot be blamed on demographic factors. The UK already has millions of young people, from very diverse backgrounds. As shown in UK Population Figures, 600,000 - 700,000 babies have been born in the UK for each of the last 10 years, and greater numbers before that. The UK already has some 15 million people under 20 (most of whom are dependents until they finish their education). If there is insufficient business talent, the reason cannot be insufficient numbers of young people.

We don't know. A declining birth rate is not the same thing as a declining population. For example, the current total fertility rate in the UK is about 1.64 children per mother and it has been steadily declining. UK population, however, is continuing to increase (by more than 200,000 a year). One reason is the addition to population caused by an excess of immigration over emigration (net inward migration). Another is natural increase (the excess of births over deaths in a year). This natural increase results in part from changes in the size and/or age structure of the population, for example, a whole generation ago. The same applies to world population - the global birth rate is falling, but world population is still increasing by about 77 million a year and will continue to increase for a long time. A population can grow faster than it did a few years before even if its birthrate is falling - this is partly due to the 'compound interest' effect of births - just as 5 per cent interest added to 00 produces the same result (50) as 4.878% on 25, so a lower birth rate can result in the same, even larger numbers, if the base population is still increasing. (A reducing population with reducing birth rates will result in compounding falls.) Changes in birth rates also take a long time to have an effect on total population size, given that each birth can lead to a life spanning several generations. Changing the direction of population growth is like steering a large tanker - it can take several generations for a decline in birth rate to lead to a stable or reducing population, from a considerably higher level.

For several reasons. One is that they may have a specific environmental problem to tackle and want to stick to their brief (for example, protecting endangered species), while leaving others to campaign on root causes such as overpopulation and overconsumption. Another reason is political correctness - touching on the sensitive subjects of procreation and migration can unleash emotional reactions and threaten sources of funds. (OPT is a small independent organisation in which no-one is paid for their work, and therefore does not have to suppress facts or controversy.) Campaigning in this area is therefore seen as an unnecessary risk for even those organisations that admit privately that population growth is a huge and fundamental environmental problem. UK public opinion indicates that these issues should not be suppressed - and since 2003 rational discussion has not been stifled. Another reason is 'population problem denial' - the belief that population numbers have no connection with environmental degradation. This doctrine does not appear to have any logical basis. Due largely to population growth, each person's ecological space has shrunk to less than a quarter of what it was a century ago, and without devastating lifestyle changes it will continue to shrink as population continues to grow. Put another way, total environmental impact and resource depletion are multiplied by the numbers of people creating impacts and depleting resources. Population problem denial may require that each inhabitant of Earth has a right to an equitable share of the planet's renewable ecological resources. Population problem denial does not recognise that ecological impact needs to be measured in the context of human numbers, nor does it recognise that nations or individuals can choose to reduce their impact on the environment by having fewer children instead of, but preferably as well as, changing their lifestyles. People who deny the problems of population growth sometimes recognise that millions of people worldwide already choose to have smaller families if given the means to do so, but then oppose family planning for wider groups of people and education about the links between overpopulation, environmental degradation and poverty. Meanwhile, more than 300 million couples worldwide are still without full family planning and reproductive health services.

Because of 'Malthusian' projections that there would not be enough food to go round for a world population of 5 billion or more. Some of these fears proved over-pessimistic in the short term. But many would argue they are coming true now, with world population at 6.3 billion and still growing by nearly 80 million a year. Two of the main topics at the World Summit on Sustainable Development at Johannesburg in 2002 were a worsening shortage of fresh water supplies and rapidly declining fish stocks worldwide. (Cod stocks have failed in Newfoundland and were in 2002 on the verge of failure in the North Sea, for example.) And according to the World Food Programme, 800 million people on Earth already suffer chronic malnutrition. In some areas of the world the proportion of a population suffering has been reduced. In real numbers, however, more people worldwide are suffering from malnutrition than ever before. The reasons given (for example, poverty, bad distribution networks, or bad government) are true but exclusive, and are much the same reasons as those given two or three generations ago. They exclude population growth, perhaps out of a desire to avoid 'sensitive' issues. Would not Ethiopia's recurring famines be easier to overcome if its population were not doubling every 28 years?

The two terms have different meanings. Carrying capacity [of the Earth, of a country or an area of land] is often taken to mean maximum population that can be provided for at a given time. Optimum population means best population. There are two reasons why we prefer the term 'optimum population'. when considering target population levels for humans. First, it implies that the population concerned is smaller than the maximum. Second, it implies that the lifestyle concerned is more than one of bare subsistence. It is extremely unlikely that people would willingly reduce their standard of living by half, for example, but quite acceptable (and already suggested by falling birth rates) that people will voluntarily have smaller families to maintain their standard of living. However, there are situations where 'carrying capacity' is the more appropriate term - e.g. in a sentence such as: 'The Earth's carrying capacity is defined by the maximum amount of renewable resources that can be consistently and sustainably produced without depleting the stock...' In considering the number of visitors the Lake District can tolerate, for example, it makes more sense to speak of its carrying capacity than its optimum population. Neither term has much real meaning when applied to humans unless it is accompanied by a specification of the lifestyle on which it is based.

This is a crucial question, because the goal of (perpetual) total economic growth can only lead to the destruction of all that supports human populations. Economics has historically relied on measurements of output in money terms, without measuring consequent environmental disbenefits. However, there are encouraging signs that economists and environmentalists are working together, and that population growth and distribution are being recognised as key factors in current political, economic, environmental and social issues. In Europe, for example, the costs of overpopulation and overconsumption are becoming apparent with the introduction of measurable environmental costs such as recycling and landfill taxes, road-congestion charging and insurance premium re-pricing resulting from the effects of global warming. There are also areas of economic growth that are 'greener' than others, and these need to be taken into account - for example, the output of 'green energy' rather than fossil-fuel energy. One economic view which is based on a simple misunderstanding of demography is that the problems caused by ageing populations are greater than those caused by growing populations - see Ageing and unemployment - This may be true in the short-term, but not in any long-term scenario. A frequent conclusion drawn from this assumption is that populations must continue to grow in order to maintain a 'young' (working) population to support the 'old' (non-working) population. If this were so, all other things being equal, world population would have to grow in perpetuity - to 10 billion, 100 billion, 1 trillion, and so on. Given a finite planet, this is a logical impossibility. Ageing is simply a phase that populations, unless life expectancy is reduced by war, famine or disease (for example, AIDS), have to go through in order to reach stability or reduction to more sustainable levels.

Fundamentally, it is short-termism and the perception of a need for perpetual total economic growth (GDP) based on material consumption that have to be questioned. If a country's population is declining but its GDP remains the same or declines more slowly, per capita economic growth can in fact increase. If that is combined with proper (short-term and long-term) measurement of environmental costs and economic growth indicators that distinguish between high-consumption and low-consumption ('green') economic activities, economics would go a long way to supporting absolute environmental necessities. It may also be more (ecologically) relevant to use purchasing power parity as an indicator of economic wealth. This measures the real purchasing power of individuals in different countries using their own currency. PPP currency values (as defined by the World Resources Institute ) reflect the number of units of a country's currency required to buy the same quantity of comparable goods and services in the local market as one US dollar would buy in an average country. A country's growing GDP can mask declining standards of living, while a country with an small population can have a high PPP - for example, Luxembourg. Without a sustainable environment, human economic activity will simply cease to exist. See Economics and More info: ecological footprinting

By specialisation in some industries and areas of activity, and by collaboration in others. The UK, as one of 15 members of the European Union, shares its collective power in areas such as agriculture and trade.

We don't know, but it isn't. Russia's population has been declining since the end of Communism, but in 2002 its GDP growth rate, at about 4.4%, was one of the highest in the world. China, whose population is growing only slowly due to a one-child population policy, achieved an 9% growth in GDP in 2003. Countries with rapidly growing populations are among the poorest economies in the world.

It depends which country. OPT does not believe that financial disincentives, even if politically feasible, are likely to be more effective than financial incentives have been in increasing the birth rate in countries where governments have pursued a pro-natalist policy. In Italy, which has a very low birth rate, financial incentives to raise births were introduced in 2003, but the effects have yet to be seen. In thinking about financial incentives to raise birth rates, few policymakers quantify the effects on population growth and the environment or realise that young people are dependents (in relation to the workforce) just as old people are. No policy will work unless it is of practical use and coincides with people's wishes. The important thing is to try to change attitudes through education: many couples, if they knew the effect that large families have on population growth and therefore the environment, might decide to stop at one or two children. Where religious belief denies access to contraception, the pressure for change needs to come from within that religious community.

No. Falling birth rates are a solution, not a problem. If you have more children to support today's 70-year-olds, you'll have more 70-year-olds in 70 years time. Then what? Have yet more children? Then even more 70-year-olds? Constantly increasing the total population by adding greater numbers of younger people may alleviate short-term problems but simply creates faster long-term population growth. If you accept that world population cannot go on growing indefinitely, this argument has no logic. There will, however, be problems for a few already overpopulated countries with 'hyper-ageing' populations, such as Italy and Japan. Ageing and hidden unemployment

Firstly, in the case of the UK the workforce is not shrinking and is not expected to shrink for about 20 years (even under the OPT Population Policy Projection A scenario). The support ratio - the numbers of working age in relation to young and old dependants - is not expected to worsen before 2012. As the state pension age for women rises to 65 the workforce will continue to grow. After about 20 years, it may fall. To get this problem into perspective, we believe it is important to remember that there are three main types of dependants in modern society: the old, the young and the unemployed. The first way to resolve the problem is to enable more unemployed people to get back to work, which can be done by more efficient labour market management, particularly by improving labour mobility and making more part-time jobs available to older workers. (The separate problem of falling pension values can only be solved by longer-term saving, extension of working lives, specific pension legal and regulatory changes and, most importantly, successful management of the economy). More info: ageing

According to the United Nations the number of migrants worldwide doubled in the 25 years to 2002, reaching a total 175 million. 175 million people live outside their country of birth with 'the majority of the world's migrants living in the developed world'. About 2.3 million migrants moved from the less developed regions of the world to the more developed regions (nearly 12 million from 1995-2000). Only one in ten of all migrants are refugees. If European populations continue to grow in the 21st century it will almost certainly be due to immigration and not to natural increase. Immigration now accounts for some 60 per cent of population growth in the UK and is expected to add nearly two million to the UK population in a decade. However, it is becoming clear to many countries that unfettered immigration cannot continue, for reasons of national security, the protection of national cultural identity or other economic, social and environmental factors. In 2002 about 40 per cent of countries in the world had policies aimed at lowering immigration levels, and developing countries were moving in a similar direction. See United Nations Population Division

Sometimes, but this should not be necessary except in extreme cases. The difficult areas are those in which a long training is needed to produce highly skilled British workers. For example, doctors and engineers. (If a settling immigrant Indian doctor with a spouse and two children replaces a permanently emigrating British doctor with a spouse and two children, it makes no theoretical difference to UK population size.) Most skills gaps, however, are due to poor labour market management, lack of mobility due to regional house price differentials, and the reluctance of employers to finance training. Since business employers have to pursue low costs to survive against their competitors, they often prefer to import trained labour to 'growing their own'. This approach, however, does not usually benefit the 'receiving' economy or the 'sending' economy, though it may benefit the employing company by lowering wage levels. If an employer imports skilled IT workers from abroad rather than retrained workers made redundant in the UK, the taxpayer has to support the unemployed British worker for as long as he or she is unemployed as well as bearing the extra environmental costs associated with additions to the population. The 'sending' country suffers a brain drain of skilled workers which in some cases can cause considerable damage to its own development prospects. The recent development of outsourcing labour from the UK to other countries may also create downward pressure on UK employment, so that to accept large-scale immigration and offer easy citizenships would add to long-term social support liabilities which are not matched by long-term benefits. See Migration