Joel Cohen
Mathematical Biologist, Rockefeller University

More People, in More Cities, Living Longer

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In 2050 there will be about 9 billion people in the world. The vast majority of them will live in urban areas, and will have a significantly higher average age than people today.

Joel Cohen

Joel E. Cohen is a mathematical biologist and Professor of Populations at Rockefeller and Columbia Universities. His research deals with the demography, ecology, epidemiology and social organization of human and non-human populations and with mathematical concepts useful in these fields. The author of 14 books, he has been honored with numerous awards, including the Sheps Award from the Population Association of America, the Distinguished Statistical Ecologist Award, the Tyler Prize for Environmental Achievement in 1999 and the Mayor's Award for Excellence in Science and Technology from the Mayor of the City of New York, Michael R. Bloomberg in 2002. Professor Cohen has been elected to the National Academy of Sciences, the American Academy of Arts and Sciences and the American Philosophical Society. He lives in New York. 
Question: What will the world’s population look like in 2050?

Joel Cohen:
So demographers agree on four big trends.  First of all, a bigger population by somewhere between 1 and 3 or 4 billion.  The middle number that people guess is 9 billion around 2050.  Right now we're almost at 7 billion, okay?  We're at 6.8, 6.9.  So next year or the year after, we're going to be at 7 billion, 9 billion.  Where are those folks going to be?  All the 2 billion people that we're going to add are going to be in poor countries in cities.  So the rural population of the world is going to level off and begin to decline, but the urban population is going to double.  So bigger population in poor countries and cities.

Secondly, the rate of growth of new young people is going to continue to fall and in some scenarios, the world will actually level off and begin to decline by 2050.  But right now we're increasing by about 75 to 80 million people a year.  By 2050, the increase will be about 33 million a year.  The rich countries, United States and Europe, will be declining by 1 to 2 million people a year, and the poorer countries will be adding 33 or 34 million people a year.  So the net will be about 32, 33, something like that.  So the rate of increase will be half as fast as now.

The third thing is: more cities.  As I said, all of the increase will be in cities.  A couple of years ago, for the first time in human history, half of humanity lived in cities.  From here on out, we're going to be more urban than rural and all of the increase will be in cities, mostly middle-sized cities.

And the fourth and last change is we're going to get older.  If you pump in fewer young people, the fraction of the population in the older age categories will increase.  Globally, the number of people aged 80-plus will quadruple.  The number of people age 60-plus will triple, and much faster than the rate of growth of the whole population, because we're only going to go up by, you know, less than 50%.  But the number of elderly people is going to go up and they're going to be in cities.  So cities are going to have a lot of old people and we haven't thought through that in the design of cities.  For example, in front of Rockefeller University, where I work every day, there's a bus stop at 63rd Street and there's a bus stop at 66th Street.  The bus stop at 63rd Street has a bench.  If you are an old person and you're going shopping, you can put your bag down there.  That's elderly friendly.  The other one doesn't have a bench and it's not elderly friendly.  We have to redesign cities to be friendly to the elderly that will be there.

So the world will have more people, it will be more slowly growing, it will be more urban, and it will be older.  Now what about the things we don't know?  We don't know how big international migration will be.  We don't know whether there're going to be millions and millions of people moving around every year, or it will be reduced because people will put up walls.  That is a choice.  My suspicion is that there will be increasing flows of people, just as there is within the European union.  They open their borders and huge amounts of flow.  I expect more.

A second thing we don't know too much about is what will families be like.  It used to be people were born, got married, and then they were dead in 20 years.  And then whoever survived married somebody else.  Now we have a huge amount of divorce and family structures are incredibly complex—meanwhile average household size in the world is decreasing.  The number of people who live together is going down and our housing stock doesn't reflect that.  So there are all kinds of questions about the future of the family, the future of households.  Will people live in communes, will elderly people live in shared facilities?  How's it going to be? We don't know the answer to that.  But those are important questions even for climate change.  You might not think of the family and climate change, but if every family has a refrigerator, then the number of people per refrigerator affects our energy consumption.

Question: What are the economic consequences of having an older population?

Joel Cohen:  It's a qood question.  And my answer is, it depends.  We know that people who are educated in their youth have better health in their old age.  And if you look in the United States over the last 25 years, age-specific disability rates have declined.  What is an age-specific disability rate?  Let's say the age-specific disability rate for 60-year-olds is the fraction of people who cannot do the normal activities of daily living, which means get out of bed, wash yourself, get dressed, and feed yourself breakfast.  If you can do that, you're fine.  Okay?  And if not, you have a disability, okay?  So the 60-year-old disability rate is the fraction of 60-year-olds who cannot do those things.  That fraction has been falling at 1-1/2% per year for the last 25 years.  People are healthier at older ages than they used to be.  I saw a t-shirt a guy was wearing that says, "50 is the new 30."  It's true!  And 60 is the new 40, okay?  If we continue, and the people among whom this improvement is the most dramatic, are the people who are educated well in youth.  That gives us a choice.  If we educate people well in youth, we can cut down the old age health care costs and disability and we have a more productive labor force, okay?  So which future do we want?  We're going to get the elderly whether we want them or not.  So are we going to have educated elderly who can fend for themselves and are in good health?  If we make that choice, a guy who's in his 60's, you might not believe this at your age, but a guy who's in his 60's has a lot of experience.  He's made a lot of mistakes, he has learned something, okay?  And from that, he can actually do things, he's got skills in his fingers.  Or a woman, I mean, you know, she's put up with her children, she's put up with her husband; she knows a lot about managing people or has technical skills, whatever, a lawyer, okay?  So you could have a very productive time.

Let me tell you my secret hope for this time.  We're going to have so few young people that we're not going to squander them on wars.  Instead of spending our best young men to go kill each other, we're going to treat them like treasures and invest in their education.  And we're going to invest in our young women and we're going to let old people wait on tables while young people go out and study.  Okay?  So that's my, this is my secret dream.

Recorded on March 5, 2010
Interviewed by Andrew Seidler