Examination of the World's Population with Joel Cohen

[Music] my name is Joel Cohen I'm professor of populations at the Rockefeller University and at Columbia University in New York City why should you consider taking a course in demography in college you will be growing up in the generation where the Baby Boomers are are going into retirement and dying you will face problems in the Aging of the population that have never been faced before you will hear more and more about migration into the United States and in some cases out into Europe and out between rural areas and cities you need to understand as a citizen and as a taxpayer and as a voter what's really behind the arguments I want want to tell you about the past present and future of the human population so let's start with a few problems right now a billion people are chronically hungry that means they wake up hungry they're hungry all day and they go to sleep hungry a billion people are living in slums not the same billion people but there's some overlap living in slums means they don't have tenure in their homes they don't have infrastructure to take the garbage away they don't have secure Water Supplies to drink nearly a billion people are illiterate try to imagine your life being illiterate you can't read the labels on the bottles in the supermarket if you could get to a supermarket 2third of those people who are illiterate are women and about 200 to 215 million women don't have access to the contraceptives they want so that they can control their own fertility this is not only a problem in developing countries about half of all pregnancies are unintended those are examples of population problems demography gives you the tools to address and to understand these problems it's the study of populations of humans and non-human species that includes viruses like influenza the bacteria in your gut plants that you eat animals that you enjoy or that Prov your domestic animals and it includes non-living objects like light bulbs and taxi cabs and buildings because these are also populations and it includes the study of these populations in the past present and future away from the using quantitative data and mathematical models as tools of analysis I see demography as a central subject related to economics to human well-being as in material terms related to the environment to the well-being of the other species with which we share the planet and culture which affects our values and how we interact with one another the key fact you need to remember is that since the inventions of Agriculture between 6,000 and 14,000 years ago the population of the Earth the human population has grown 1,000 fold from approximately 7 million maybe 14,000 years ago to nearly 7 billion this year put three zeros on the end of 7 million you get 7 billion over the same interval the Earth has not gotten any bigger the continents haven't expanded a thousandfold or at all the oceans are the same size as they were before the atmosphere is the same size as it was before so the question that concerns a lot of people and me is whether the impact that 7 billion people or more in the future will have on the earth will endanger our own well-being and the well-being of other species on the earth we know that humans have already caused the extinction of many species question is is that going to come back and bite us and if so in what ways demography provides us with a reliable way to imagine and to reimagine the Future so let's get down to some nitty-gritty details here about 2,000 years ago there were roughly a quarter of a billion people on the planet today there are almost 7 billion more than 67th of that growth in fact more than 67th of the growth since the beginning of humans 50,000 years ago has occurred in the last 200 years to go from a quarter of a billion to half a billion took 16 centuries so we reached about half a billion humans about 1,600 more or less the human population of the Earth if it were growing exponentially would go from a quarter of a billion to half in 16th centuries and from half to one in another 16th centuries what actually happened was that the human population of the Earth reached a billion around 1800 because of food stuffs that came from the new world to the old notably potato and corn or Maze and because many of the people who were overcrowded in Europe went to America where there were fertile and unoccupied lands to use so the East West Exchange the Colombian Exchange across the Atlantic liberated population growth in the European sector there was a similar development in Japan an acceleration of population growth around the same time in 1800 the Industrial Revolution began and the population doubled from 1 billion to 2 billion by 1930 1927 we don't know exactly why don't we know exactly because we didn't have censuses that covered the whole world at that time so it's a retrospective guess so our in times went from 1600 years to 200 years 1600 to 1800 to 130 years 1800 to 1930 the next doubling from 2 billion to 4 billion took only 44 years 1974 so until the last half century human population growth has been faster than exponential but this slide that you've been looking at is like a shower curtain what it reveals is a little less interesting than what it conceals and so I'd like to zoom in on the part of history from 1950 to now we've zoomed in to the last 50 years the red vertical line on the slide is now and it begins on the left side in 1950 and runs up to 2000 and what you see is that the annual population growth rate reached a peak of about 2. 1% per year in the Years 1965 to 1970 and since then has fallen by half to about 1. 1% per year so for the last 2000 years at least except for the black death in The 14th Century the population growth rate was going up up up up up and around 1965 it began to decline if you look there's a sharp dip before 1965 a very sharp Valley that is the Great Leap Forward in China which killed about 30 million people unnecessarily but the global peak of 2.

1% per year has since led to a declined by a half so in absolute terms and in percentage terms the number of people we're adding to the planet has begun to slow since 1950 humans have made the swiftest voluntary change in reproduction in human history around 1950 the average number of children per woman per LIF time was very close to five today the average number of children per woman is about 2. 5 or 2. 6 in other words billions of people have changed their reproductive Behavior to lower the number of children born in a lifetime from 5 to two and a half but not everywhere in subsaharan and Africa the decline has been much less from perhaps 6.

6 children to 5. 1 over the second half of the 20th century to understand the consequences of this fall to two and a half children per woman you need to know what is meant by replacement level fertility so I am going to introduce that by telling you about the theory of bathtubs a regular bathtub with no stopper water comes in and water goes out now water coming in corresponds to births to the earth and water going out corresponds to death and the level of the bathtub corresponds to the total population size so if the number of births just matches the number of deaths the population stays steady and that's the replacement level fertility now you're asking yourself what is the replacement level of fertility the answer is about 2. 1 children per woman there has been an amazing transformation in the distribution of fertility across the world in the last half century I want you to look carefully at this Slide the vertical line is replacement level fertility the horizontal axis is total fertility children per woman per Lifetime and the vertical axis is the percent of world population so it's zero at the bottom a quarter half 75% and 100% at the top in 1950 the black line that's at the bottom practically everywhere women were having more than replacement level fertility they are on the right of the red line by 19 75 roughly a quarter of women had moved to the left of replacement and three quarters were still over to the right in 2003 this was not in any newspaper anywhere but it was a very important event in 2003 half of all the women in the world were having replacement level or less they moved to the left of the red line and now more than half of humanity lives in a country at or below replacement level fertility it's the first time in human history that this has happened and it's important but you remember that the total fertility rate the average number of children per woman is at 2.

5 not 2. 1 and that's because on this curve the green curve the folks with high fertility are further to the right of the red line than most of the folks with low fertility are to the left so the average is skewed to the right so we still have a growing population but this change is continuing and how fast it continues is something that you as voters as potential scientists as Citizens will influence by what you choose to do about the 215 million women who have an unmet need for contraception so much for the past let's go on to the present this is a population pyramid it's one of the basic descriptive tools of demography and you should understand what it is let's start with the left side of the picture the horizontal axis the width of the bar tells you how many people there are and the vertical axis corresponds to age group so the lowest bar is for people aged 0 to 4 with males on the left and females on the right the next bar is people aged 5 to 9 the top bar is 85 or 90 and what you see is that in the rich countries there are about as many people aged let's say 0 to four as there are aged 85 or 90 but it's basically a slender column now compare it with the age pyramid for the poor countries the base of the pyramid is enormous compared to the number of elderly so there are many more workers to support the elderly per elderly person the width of the bar again is number of people so in the ranges from 5 to 14 or 5 to 19 that's the school age population it means that the challenge of educating those children is much greater in the developing countries than it is in the rich countries because those bars keep getting wider as the developing countries pump in more children at the bottom of the pyramid the age groups move up with time as they get older and so the larger school age population is followed 10 years later by a much larger military age population so if you look at the age groups 15 to 30 you can see that the potential military force in the developing countries vastly exceeds that in the rich countries it doesn't mean it's military power for them it means they can afford a military engagement in a way that the human resources of the rich countries make very difficult increasingly difficult so where's the growth going the demographic growth is happening in the countries that can least afford to deal with the additional population what's the average income the reason we call a rich countries rich is that their average income is about $32,000 a year per person and in the poor countries it's about $5,000 a year what fraction of people are living on less than $2 a day nobody lives on less than $2 a day in the rich countries and 51% just about half in the poor countries in other words about three and a half billion people on our planet are living on $2 a day or less you might ask yourself if things are so bad there how is it that their population is growing so rapidly and the fact is that the difference in death rates is much smaller than the difference in fertility rates so even though a higher fraction of children die before they reproduce the average number of children that people have when they do reproduce in the poor countries more than compensates for the increase in the death rate so that's why we have rapid population growth at the same time that we have high mortality because we have even higher fertility it's an important job general question how does the rich World benefit from the prosperity and development of the poor World there are lots of different answers you can give one is purely economic richer people in China and Africa will buy more American music CDs and more movies and more software and more Hightech engines from General Electric and more products because they have more means to buy so that's one kind of an answer a second is public health there are millions of flights in both directions from the poor countries to the rich countries every year and the microbes don't know about passports and they cross from Mumbai to New York just as fast as they go from New York to Mumbai and when there are outbreaks of drug resistant tuberculosis those can travel around the world and they pose a danger to me and to you guys so we have an interest in the health and well-being a direct personal interest in the health and well-being of people in poor countries so now we've talked about the demographic past and the demographic present and next we're going to talk about the demographic future Woody Allen said eternity is very long especially near the end so we're not going to talk about eternity we are only going to talk about the near-term future how much of the future is relevant to you well according to the United States life taes published by the national Center for Health statistic an 18-year-old in the United States in the year 2011 has a 91% chance of surviving to 2050 91% based on survival rates in 2006 if you behave wisely and if economic and medical progress continue you have at least that good a chance of making it to 2050 so we're going to talk about the world from now to 2050 I can say with confidence that four things will happen over the next 40 years or so the world's population will get bigger it will grow more slowly it will be older in the sense that the fraction of older people will increase dramatically and it will be more urban and I'm going to go through each of those four to explain some of the details what we don't know too much about is what will be the future of migration the future of household structures and the future of families we have some ideas about that but that's relatively less certain this graph shows curves of the history and future population out to 2050 at the top the curve shows the anticipated population if fertility remains at the level it is today and there's no further decline in fertility that's called the constant fertility assumption and it shows that the world would go to about 11 billion people by 2050 however if fertility drops as it has dropped in the past the medium projection of the UN population division is that population would rise to about 9. 1 billion by 2050 so that's a difference of 2 billion in other words we're counting on a continuing decline in fertility to lower the population size by about 2 billion by 2050 what we do between now and 2050 will have a huge impact on how difficult it is to feed House Shelter educate and provide health for for the billions of people on the planet in 2050 it will affect an enormous range of human problems it's possible that population growth would end before 2100 depending on the choices we make now what choices am I talking about choices like educating women providing credit to women in countries where women are not now allowed to have credit providing reproductive health care so that women are not forced as they are in some countries to have children when they don't want to raising the age at marriage so that 12 year olds 13y olds and 14 year olds aren't put into marriage there's a lot of things we can do to raise people including even women raise people's control over their own lives and we should be doing those things the second fact about the future is that the population is going to grow more slow the slowing will depend on what we do now by 2050 in the medium projection from the United Nations population division the world will be growing by 31 million people a year what's it doing now it's growing by 76 million people a year in the poor countries population will be growing by 32 million a year while in the rich countries population will actually be declining by a million people a year all already today in 2011 population is declining in more than 50 countries not well known What's Happening Here is a shift in childbearing desires and action from quantity to Quality as people urbanize as people get educated as wealth improves people are making greater investments in a smaller number of children so we've talked about population size growth rate the next is aging so by 2050 there will be about three times as many elderly as children this is the first time in human history that the elderly population has outnumbered the young population so what who cares well aging affects energy demand so even if you're interested in the environment you need to know about the age structure of populations older householders at least in the United States India and China the three countries where it's been studied in detail spend more than younger households measured by the age of the head on utilities services and Health Care utilities are the most energy intensive part of the household budget that's not the only reason to care the rise in the fraction of elderly poses an increasing challenge to a relatively reduced number of workers and it's possible that the well-being of elderly people could improve if they're educated or could get worse if they are warehoused in old people's homes we know for example that people who are educated in their youth have much lower disability when they get older and in fact disability rates at any given age in the United States have been dropping by about 1 a half% per year for the last 25 years so there are far fewer disabled elderly now than they used to be that's the meaning of 60 is the new 40 50 is the new 30 people are healthier at older ages that's a result of investment in education in youth so there are policy implications for a rising aged population we better invest in educating people when young and the last of the four topics is cities and I'm going to give you a very simplified and boiled down demographic history of the first half of the 21st century in 2000 you could divide the world into two equal parts half Rural and half Urban so that was about 3 billion Rural and 3 billion Urban in 2050 the rural population will still be at 3 billion and the urban population will have doubled from 3 billion to 6 billion all of those additional 3 billion Urban people will be in poor countries the equivalent of a city of 1 million people will have to be built every 5 days from now to 2050 and all of them in poor countri countries so what's the consequence what does this massive shift towards urbanization mean if we underinvested cities we can go from a billion people living in slums today to four billion people living in slums and if we invest in the cities if the real estate companies realize the opportunities the incredible demand that people have to live in decent housing we could reduce the size of the slot so I cannot give you a deterministic picture I can tell you what's what would be awful we could have infectious diseases rampant we could have Warfare in the cities we could have disorder but that's not necessary we could have clean water supplies we could have security for people in their houses that doesn't get as much news attention but the point I I want to make is we have choices about the future of cities and many things about urbanization are positive and I want to tell you a few of the things that are positive not because they're automatic but because they are positive in fact and because we can enhance the positive compared to rural areas urban areas have lower fertility rates why I'm a woman on the farm you might not think so but I am okay I'm a woman on the farm the more children I have the more help I can have in collecting the water collecting the firewood and attending to the goats and sheep as soon as I move into a city those children convert from an asset to a liability I have to buy them clothing I have to send them to school there are school fees the apartment is too small the incentives completely shift Direction Urban ation makes people want to have fewer children cities also have higher usage of modern contraception and lower unmet needs for contraception why I am a woman you might not know it I don't have to walk 15 miles to the nearest health center and be exposed to the inspection of my husband's friends when I go in for contraception no when I'm in the city I just go around a corner and it's Anonymous so urbanization brings many features of Liberation as well as changing the incentives cities concentrate economic productivity 80% of the world's gross domestic product is produced in cities although there are only 50% of the world's people in cities cities generate cultural assets educational resources Public Health Resources Medical Care and they can promote Energy Efficiency Let me Give an example this graph shows the passenger transport carbon dioxide per person the denser the city the lower the amount of carbon dioxide per person New York City is reported according to the mayor's office to have less than onethird the carbon dioxide emissions per person of the US average people take the subway people ride the bus cities also have hazards many cities are built along coastlines coastlines are where the continental plates of the oceans collide with the continents that means they are prone to earthquakes we just had the big example in Japan but it's true all around the world the ring of fire around the Pacific Ocean coincides with where the cities are because cities are coastal a lot of the world's Urban people live near the coastline and that's where the subduction zones are in California I'm going to show you three slides of New York City where I live this is New York City as it is now the Red Zone will be underwater if the water level rises by 1 meter on the average one meter is probably more than we'll have in the next 50 years but could easily happen by the end of the century at current rates now a 6 meter rise would happen if the Greenland and Antarctic Ice masses melted 6 m is about 20 ft that would be a catastrophe in many respects including for me there's a little place over here in New Jersey which is my favorite nudus colony and it would be completely underwater so that would be a terrible thing to happen so cities are vulnerable to rising sea level to Coastal storms cities concentrate people so they're vulnerable to infectious diseases water supply attacks and cities are excellent targets for military and terrorist attacks as we know in New York City and many other cities used to be battles were fought on Battlegrounds no more they're fought in cities and that will increasingly be the case As Cities concentrate assets Urban growth could affect the food supply right now cities occupy 3% of the land surface of the Earth the arable land the land where we can grow food well is about 10 or 11% of the land surface of the Earth it's not surprising that many cities are smack in the middle of the best arable land because that was where a food surplus could be easily produced without having to ship the food now if cities are going to double we have another Choice do we double the air area from 3% to 6% and eat up our arable land literally or do we double the density and keep the areas of the Cities constant at 3% this is a choice for the future and it depends on zoning and culture and real estate developers and economics and choices that we make as Citizens how do we address the problems we have there are three kinds of solutions that people have put forward bigger Pi fewer Forks better manners the bigger Pi people say we should use technology to increase production the fewer Forks people say we should use contraception to reduce population growth and we should consume less material products and the better manners people say we should eliminate violence inequities between men and women inequities between rich and poor inequities between young and old we should eliminate irrational subsidies and just make things work more efficiently get rid of corruption I took a few years to try to figure out what's my best way to support those three strategies all of them and I came to the conclusion that the best response would be to educate all children boys and girls well for 10 to 12 years high quality primary and secondary education I realized there's no chance of educating people if their brains haven't been fed adequately in Udo and after birth especially for the first three years so I am now moving around to working on the problem of getting food adequate good food to pregnant women lactating Women and Infants up to the age of three because there are many countries where by the time a child gets to school it's too late the brain has lost its capacity to learn so now we're talking about food I started this conversation saying that there are a billion hungry people people chronically hungry I want to come back to this we depend on other species here is a list of what other species provide to humans and I'm going to read the list because it's important Food for People feed for our domestic animals fuel biofuel for example and W to burn biomass and in many countries people burn d the waste products of animals that's an important source of fuel fiber so we depend on trees for many paper and other products Fascination we love to go to the zoo and see animals we love to see wildlife when people go out in nature they're thrilled if they see a deer or some other kind of wildlife in fact in Central Park the German tourists are thrilled to see squirrels we find animals fascinating Pharmaceuticals most of our drugs are natural products tuned up to serve human needs animals provide transport they carry people places they provide traction they pull plows they pull carts other species provide symbioses I've talked about the animals not the animals the bacteria that live in our guts and they provide infection they can cause disease so the question I want to address now is can we grow enough food to bring us to 2050 without catastrophe these are data from the food and agriculture organization in Rome there are estimates of the number of people in the world who are chronically undernourished day after day the current estimate is about 925 million people that's nearly a billion and it is higher than the number has been in the last 40 years 98% of these people live in poor countries not only poor countries here is something that shocked me and I hope it will shock you at some point during 2009 17.