In 2011, the population of the earth will reach 7 billion. It takes 200 years to count to 7 billion. 7 billion steps would take you around the globe 133X.

Population through the ages.

1800 – 1 billion – It took 250,000 years to reach the first billion.

1927 – 2 billion – 127 years

1959 – 3 billion – 32 years

1974 – 4 billion – 14 years

1987 – 5 billion – 13 years

1999 – 6 billion – 12 years

2011 – 7 billion – The first time it took to add 1 billion increased.

2025 – projected to be 8 billion.

2050 – projected to be 9.3 billion

2100 – Science Magazine, in October 2014, predicted there would be 10.9 billion people

Every second, 5 people are born and 2 people die.

Everywhere we are living longer, the average life span: 1960 – 53 years, 2010 – 69 years.

Standing shoulder to shoulder, all 7 billion would fill the city of Los Angeles.

It is not space we need, but balance: 5% consume 20% of the worlds energy; 13% don’t have clean drinking water. 38% don’t have adequate sanitation; 2.6 billion live on less than $2/day. The richest 86 people on earth have as much wealth as the poorest 3.5 billion people.

11% of the earth’s land is used to grow food.

Odd though it seems, the growth of the world’s population is actually slowing. The peak of population growth was in the late 1960’s, when the total was rising by almost 2% per year. Now the rate is one-half that. The last time it was that low was in 1950, when the death rate was much higher. The result is that the next billion people will take 14 years to arrive, the first time that a billion milestone has taken longer to reach than the one before. The billion after that will take 18 years.

There are probably already too many people on the planet. But the notion of “too many” is more flexible than it seems. The earth could certainly not support 10 billion hunter-gatherers, who used much more land per head than modern farm-fed people do. But it does not have to. The earth might not be able to support 10 billion people if they had exactly the same impact as 7 billion do today. But that does not necessarily spell doom because the impact humans have on the earth and on each other can change.

The big questions about population are: can the world feed a 9 billion mouths by 2050? Are so many people ruining the environment? And will those billions, living cheek by jowl, go to war more often? On all three counts, surprising as it seems, reducing population growth any more quickly than it is falling anyway may not make much difference.

Start with the link between population and violence. It seems plausible that the more young men there are, the more likely they will be to fight. This is especially true when groups are competing for scarce resources. In 2014 there were 1.8 billion 18-24 year-olds, a historic high. Governments are warned that they need to invest in youth education, health and job prospects or face political instability. Some argue that the genocidal conflict in Darfur, western Sudan, was caused partly by high population growth, which led to unsustainable farming and conflicts over land and water. Land pressure also influenced the Rwandan genocide of 1994, as migrants in search of a living labour force to productive use. In the 1980’s, Latin America and East Asia had similar demographic patterns. But while East Asia experienced a long boom, Latin America endured its “lost decade”. One of the biggest questions for Arab countries, which are beginning to reap theri own demographic dividends, is whether they will follow East Asia or Latin America. But even if demography guarantees nothing, it can make growth harder or easier. National demographic inheritances therefore matter. And they differ a lot.

The world can be divided into three categories according to levels of fertility. About a fifth of the world lives in countries with high fertility – 3 or more. Most are Africans. Sub-Saharan Africa is one of the fastest growing parts of the world. In 1975, it had half the population of Europe. It overtook europe in 2004, and by 2050 there will be just under 2 billion people there compared with 720 million Europeans. About half of the 2.3 billion increase in the world’s population over the next 40 years will be in Africa. The rest of the world is more or less equally divided between countries with below replacement fertility (less than 2.1) – Europe, China and the rest of East Asia, and those with intermediate fertility (between 2.1 and 3) – South and SE Asia, the Middle East and the Americas (including the US but not Canada).

The low fertility countries face the biggest demographic problems, The elderly share of Japan’s population is already the highest in the world. By 2050 the country will have almost as many dependents as working-age adults, and half the population will be over 52. This will make Japan the oldest society the world has ever known. Europe faces similar trends, less acutely. It has roughly half as many dependent children and retired people as working-age adults now. By 2050 it will have three dependents for every four adults, so will shoulder a large burden of ageing, which even sustained increases in fertility would fail to reverse for decades. This will cause disturbing policy implications in the provision of pensions and health care, which rely on continuing healthy tax revenues from the working population.

At least these countries are rich enough to make such provision. Not so China. With its fertility artificially suppressed by the one-child policy, it is ageing at an unprecedented rate. In 1980 China’s median age (the point where half the population is older and half younger) was 22 years, a developing country figure. China will be older than America as early as 2020 and older than Europe by 2030. This will bring an abrupt end to its cheap labour manufacturing. its dependency ratio will rise from 38 to 64 by 2050, the sharpest rise in the world. Add in the country’s sexual imbalances – after a decade of sex-selective abortions, China will have 96.5 million men in their 20s in 2025 but only 80.3 million young women – and demography may become the gravest problem the Communist Patty has to face.

Many countries with intermediate fertility – SE Asia, latin America, the US – are better off. There dependency ratios are not deteriorating so fast and their societies are ageing more slowly. Americas demographic profile is slowly tugging it away from Europe. Though its fertility rate may have fallen recently, it is still slightly higher than Europe’s. In 2010 the two sides of the Atlantic had similar dependency rates. By 2050 America’s could be nearly ten points lower.

The biggest potential beneficiaries are the two other areas with intermediate fertility, India and the Middle East, and the high fertility continent of Africa. These have long been regarded as demographic time bombs, with youth bulges, poverty and low levels of education and health. But that is because they are moving only slowly out of the early stage of high fertility into the one in which lower fertility begins to make an impact. At the moment, Africa has larger families and more dependent children than India or Arab countries, and a median age of 20 compared with their 25. All three areas will see their dependency ratios fall in the next 40 years, and they will keep their median ages low – below 38 in 2050. If they can make their public institutions less corrupt, keep their economic policies outward-looking and invest more in education, then these 3 areas could become the fastest growing parts of the world economy within a decade or two.

If you look at the overall size of the world’s population, the picture is one of falling fertility, decelerating growth and a gradual return to the flat population level of the 18th century. But below the surface societies are being churned up in ways not seen in the much more static pre-industrial world.

CITIES – One Solution to Dealing with 7 Billion People

2008 was the first year that more of us lived in cities than rural areas. Rome was the first city to reach 1 million people in 13 BC. In 1800 only London, Beijing and Tokyo had more than 1 million people. By 1900, there were 16 , 1950 – 74, and in 2010 – 442 (China-89, India-48, US-42, Brazil-21, Mexico-12). In the 19th century, London was the only city of more than 5 million, now there are 54, most of them in Asia. A megacity has a population of >10 million people: 1975 there were 3, 2011 there were 21.

In 2050, 70% will be living in urban areas. Most urbanites live in cities of less than half a million, but big cities have gotten bigger and more common. Urbanization is now good news. With Earth’s population population headed for 9 or 10 billion, dense cities are looking like a cure – the best hope for lifting people out of poverty without wrecking the planet. There is no such thing as a poor urbanized country; there is no such thing as a rich rural country.

Poor people flock to cities because that’s where the money is. Cities produce more because the absence of space between people reduces the cost of transporting goods, people, and ideas. Historically, cities were built on rivers or natural harbours to ease the flow of goods. But these days, since shipping costs have declined and service industries have risen, what counts most is the flow of ideas. Wall Street is the quintessence of a vibrant city with the trading floor forsaking large offices to work in an open plan bath of information – they value knowledge over space, enabling people to learn from one another. In cities with higher average education, even the uneducated earn higher wages – that’s evidence of “human capital spillover”. Spillover works best face-to-face. No technology yet invented – the telephone, internet, or videoconferencing – delivers the fertile chance encounters that cities deliver. Nor do they deliver the nonverbal, contextual cues that help convey complex ideas.

Economists embrace cities as engines of prosperity. Environmentalists have taken a bit longer. By increasing income, cities increase consumption and pollution. Nature is lost, but the alternative is spreading the damage. From an ecological standpoint, a back-to-the-land ethic would be disastrous. Cities allow half of humanity to live on around 4% of the arable land, leaving more space for open country. Per capita, city dwellers tread more lightly in other ways. Their roads, sewers and power lines are shorter and so use fewer resources. Apartments take less energy to heat, cool, and light than do houses. Most important, people in dense cities drive less. Destinations are close enough to walk to, and public transport is practical. In cities, like New York, per capita energy use and carbon emissions are much lower than the national average. Cities in developing countries are even denser and use far fewer resources. But that’s mostly because poor people don’t consume much. Slums may be a model for low emissions, but its residents lack safe water, toilets, and garbage collection. A billion other city dwellers in developing countries tolerate the same. By 2050, cities will have absorbed most of the worlds population increase to 2 billion.

Developing countries are responding by trying to make migration to cities stop. It’s a mistake to see urbanization as an evil rather than an inevitable part of development. The problem is not the number of people but the inability to govern them.

Seoul is a good example on how to manage rapid urbanization. After WWII and the Korean War which ended in 1953, more than a million refugees migrated to the bombed out city. Between 1960 and 2000, Seoul’s population zoomed from fewer than 3 million to ten million, and South Korea went from being one of the world’s poorest countries, with a per capita GDP of less than $100, to being richer than some of Europe. The speed of transformation shows in the homogenous row of concrete apartment blocks. Rapid improvements in public health and nutrition, and an economic boom fueled by the growing city paid for the infrastructure that helped absorb the growing population. The cities growing middle and upper classes left the old Seoul for high-rises and a grid of boulevards. Initially the poor were unable to afford the high-rises, but over the years, the rising population has been able to cash in on the housing boom. Today half of the population of Seoul live in apartments. Today Seoul is one of the densest cities in the world. It has millions of cars but also an excellent subway system. The streets are vibrant with commerce and crowded with pedestrians, each of whom has a carbon footprint less than half the size of New Yorker’s. The country has gone from 28% urban in 1961 to 83% today. Life expectancy has risen from 51 to 79 years. Korean boys are 6″ taller than they used to be.

Greenbelts were built in many cities to halt further development. They preserved open space, but rarely stopped the growth of cities. They have had the effect of pushing people farther out, sometimes absurdly far. People now commute from suburbs leapfrogging the restraints. When you try to stop urban growth, you amplify sprawl. Greenbelts aren’t the cause of sprawl as most cities don’t have them. Other government policies, such as subsidies for highways and home ownership, have coaxed the suburbs outward. So has that other great shaper of density of cities – the choices made by individual residents as a lot of people want nice houses with gardens. Even in developing countries, most cities are spreading out faster than people pour into them – on average they are getting 2% less dense each year. By 2030. their built up area could more than triple. The expansion is being driven by rising incomes to buy more space and cheap transportation.

In the 20th century, American cities were designed around cars that have made city air unbreathable and carry suburbs beyond the horizon. Car-centered sprawl gobbles farmland, energy, and other resources. Now city planners want to repopulate downtowns and densify suburbs. Urban flight, which seemed like such a good idea a century ago, now seems like a wrong turn. Meanwhile in China and India, car sales are booming along with suburban sprawl. But it would be much better for the planet if dense cities were built around the elevator, rather than the car. Urban planning requires looking decades ahead – looking at growing cities in a positive way – as concentrations of human energy to be organized and tapped. Sustainability means not designing around cars, being able to walk to the center of town to shop, or catch transportation to jobs. Preserving large, semiwild parks where citizens can commune with nature and expand along railway and subway lines. Get the transportation right and then let things happen.