De bevolkingsexplosie: probleem
of kans ?
Gerard Govers KU LeuvenHet probleem
• HUMO Een verdubbeling van de bevolking om de veertig jaar: kan je die cijfers extrapoleren naar de hele wereld? ‘Vermeersch «Nee, want op wereldvlak is het nog erger gesteld. We zitten nu aan bijna zeven miljard mensen. Maar als iedereen blijft denken dat hij of zij recht heeft op vier kinderen, verdubbelt de bevolking met elke generatie. Als we gewoon blijven voortgaan zoals nu, zitten we over zes, zeven generaties met 1000 miljard mensen op aarde. Dat is te veel, dat snapt elke kleuter. (schudt het hoofd) Natuurlijk zullen we nooit aan 1000 miljard raken. Want vooraleer het zover komt zal de aarde getroffen worden door verschrikkelijke hongersnoden, epidemieën en oorlogen. De plunderingen in Haïti: dat wordt de realiteit van alledag. De genocide in Rwanda ‐ toch een van de gruwelijkste oorlogen die we de laatste jaren hebben gekend ‐ was het gevolg van overbevolking. Waarom hebben die mensen mekaar uitgemoord? Uit plaatsgebrek, natuurlijk. ‘Others are worried too
June 2017
But some of those have bad timing…
We moeten de bevolkingsgroei
stoppen….
• Er zijn steeds meer kinderen (vooral in arme landen) • Die gaan ook weer meer kinderen hebben ! • Etc….Dit leidt tot een ongecontroleerde
bevolkingsexplosie !
But not everyone agrees:
• https://www.youtube.com/watch?v=KbwNgI_gFMI • https://youtu.be/vZVOU5bfHrMSo, we need to consider in more detail
what is going on ?
• Is the world population spinning out of control ? • What controls population growth ? • What can be done to limit it ?Planning should be knowledge based
• So, how good is our knowledge ? • What do we know ?Let us take a simple quiz
• Questions will appear at: www.pollev.com/gerardgovers076 The quiz is a modified version of the on developed by Hans Rösling: http://edition.cnn.com/2013/12/10/world/gap minder‐us‐ignorance‐survey/So, it appears we can use an update
• This lecture will cover the basics of global
population dynamics
• The material is essentially non‐mathematical
But let us start with some math:
exponential growith
Exponential growth
rN
dt
dN
N= size of population t= timer=per capita growth rate per capita, also difference between birth rate, b, en death rate, d, so r=b‐d
Integration results in:
rt c c rt N e e N e e c rt N c rt c N rdt N dN
ln ln 2 1 lnWe can solve for e
0by setting the time
to 0:
c r ce
N
e
e
N
0 0 0 rte
N
N
0 So that we can write :rt
N
N
t
ln
0
ln
Or:This may look very unfamiliar to you
but your bank is using it all the time
This is what your bank does when it calculates how your capital ‘grows’ due to interest:
N
t+1=N
t(1+r)
r=fractional growth rate
Or: each year we add an amount of interest to the capital which we calculate as a fraction of that capital (e.g. 2%)
Graphically: evolution of cell phone
users in USA (thousands)
Most important properties
• Exponential growth accelerates over time because a fraction of what is already there is being added every year • Exponential growth does not have any limit: the capital/population can exceed any fixed threshold if there is a sufficient amount of time
This is the model that Etienne
Vermeersch implicitly uses
• Each family has more than two children • These children will also have more than two children… • Etc., etc., ../…Does he (and others, like Ehrlich) have
a point ?
Exponential growth results on a linear
relationship between N and time on a
semilog paper
0 500000 1000000 1500000 2000000 2500000 3000000 3500000 4000000 4500000 5000000 0 2 4 6 8 10 12 14 16 Growth of mobile phone usage 1 10 100 1000 10000 100000 1000000 10000000 0 2 4 6 8 10 12 14 16 Growth of mobile phone usageBevolkingsgroei op Aarde
0,00E+00 1,00E+09 2,00E+09 3,00E+09 4,00E+09 5,00E+09 6,00E+09 7,00E+09 0 500 1000 1500 2000 2500 Po pul at io n Year (AD) Evolution of population World population Asia Western Europe Western offshoots AfricaIs dit exponentiële groei ?
Groei is dus sneller dan exponentieel
1,00E+05 1,00E+06 1,00E+07 1,00E+08 1,00E+09 1,00E+10 0 500 1000 1500 2000 2500 Po pul at io n (l og ax is) Year (AD) Evolution of Population World population Asia Western Europe Western offshoots AfricaGroei is super‐exponentieel
• Is een proces dat niet kan blijven duren omdat hulpbronnen uitgeput geraken • Bevolkingsgroei is nu 1% per jaar: reken even uit wat de bevolking van de Aarde zal zijn in 2117 ?Answer:
• Ca. 20 billion !Vraag: zal het blijven duren tot het
systeem Aarde in elkaar stort ?
• Om die vraag te kunnen beantwoorden: – Analyse van bevolkingsgroei in het verleden –Deze analyse gebruiken om een zo goed mogelijke voorspelling te doenPopulation evolution varies widely
0 20000 40000 60000 80000 100000 120000 140000 1650 1700 1750 1800 1850 1900 1950 2000 2050 japan ethiopia germany
A relative graph is clearer (1910=100)
0 100 200 300 400 500 600 700 800 900 1800 1850 1900 1950 2000 2050 japan ethiopia germany world
So what is going on here ?
1,00E+05 1,00E+06 1,00E+07 1,00E+08 1,00E+09 1,00E+10 0 500 1000 1500 2000 2500 Po pul at io n (l og ax is ) Year (AD) Evolution of Population World population Asia Western Europe Western offshoots Africa Industrial Revolution
The curves show a rapid increase from
ca. 1750‐1800
• What happened in that period ?
Industrial revolution
Industrial Revolution
• Official start: invention of steam engine by James Watt (1762) • Was a further development of existing engines (Newcomen engine, 1712) • Dramatic change of working conditions –Emergence of factories&mines where people worked in dreadful conditionsSo, not really a happy time
Question: did the Industrial Revolution
lead to an increase or a decrease in
mortality ?
John Constable, The Haywain, 1821
The answer is somewhat surprising: mortality declined right from the beginning of the IR Oded, 2012 From the start of the 18thcentury in England/Wales, somewhat later in other European countries, but serious decline starts after 1780 in all Western European countries
Why is this ?
• Basic change : use of fossil fuels to produce
mechanical energy
–Total annual useful energy production of a grown man: 0.075*10*300= ca. 225 kWh per year or 225*1000*3600=810Mj (1 kWh=1000*3600 Ws=3.6Mj), or ca. 2 MJ per day –1 kg of wood: 15 MJ –1 kg of glucose : 20 MJ –1 kg of coal: 30 MJ –1 kg of diesel: 50 MJ –1 kg of hydrogen: ca. 143 MJ –1 Kg of Li‐ion battery: 0.72 MJ –1 kg of Uranium: 79.5E6 MJ
To put this in perspective
• The physical labour that a healthy human male can perform in one year is energetically equivalent to ca. 16 liters of diesel=
1 full year of this: The energy needed to heat a house in Belgium is equivalent to the physical work of 100 people =A very nice illustration:
https://www.youtube.com/watch?v=C93cL_zDVIM
Industrial revolution=development on
speed due to increased energy availability
Industrialisation causes a chain
reaction of changes leading to a
FUNDAMENTALLY different society
Energy Workers Socialis m Trainin g Health care Reduced religious influenc e Capital Migrati on Urbanisation State organis ation Agricul ture Scie nce nu trit ionWould you train these workers: yes or
no ?
If people get training
• They will work better, so you will make more profit • You will have to replace less people • They will be better able to adjust to changesBut also…
• They will be better able to follow a medical treatment • They will better understand what makes them ill (and avoid it) • They will become better at expressing their needs and requesting change…Changes led to a dramatic reduction in
mortality
• Better information
• Better medication
• Better food
• Better government institutions
One example….
What explains the mortality decline ?
• Health
–Improved health care –Improved medicins
•Vaccinations: from ca. 1785 Antibiotics: from 1928 (Fleming)
–Sanitation
•John Snow 1854: link between cholera and trinking water
• Improved food provision
•Food sterilisation (1810) •Improved yields (Fertilisation,
von Liebig (1840))
What explains the mortality decline ?
• Level of development and education
–Hygiene
–Therapy adherence
• Governmental action
–Sanitation: sewage disposal, garbage removal,
planning
–Establishment of medical‐social care systems
First vaccinations
• Smallpox killed 8 to 20% of all people in the 18th century
• Inoculation (scarring) with scabs (korstjes) of people having smallpox (pokken) reached Europe around ca. 1724 (Lady Montagu (writer and Turkish Ambassador of the UK) authorised the inoculation of her son by the Embassy surgeon in 1716. Scientific description in 1724. Jenner developed a (safe) vaccine from cowpox after noting that milkmaids did not get smallpox in 1796.
John Snow
• Discovered that there was a geographical connection between cholera outbreaks and location of water pumps/wells
Mortality could be greatly reduced by simply shutting off infected pumps
Level of development and education
Galor, 2012
Government action: water quality
• Generally important improvement over the last decade• is in fact in many cases 2nd
wave of improvement • first wave due to better treatment of mainly household water • second wave related to better treatment of household+industrial waste with modern techniques (taking care of chemical pollution as well)
Important
• This progress is not directly coupled to economic growth (wealth), but rather to improved societal conditions/better science/better technology • Changes driven by same processes that lead to economic growth but there is no direct, causal link between income level and mortality level: it has more to do with how society works (think Cuba) • Clearly, increase in available income made progress possible (think of sewer systems)The transition started (much) later in
other countries
• Decline of mortality starts when countries get
integrated in global, industrial, capitalist system
• In Europe of the 19th century this happened
when the industrial revolution reached a country
It took about 50 years to reach E
Europe
Oded, 2012 From the start of the 18thcentury in England/Wales, somewhat later in other European countries, but serious decline starts after 1780 in all Western European countriesBut also in these other countries
mortality declined right from the start
Timing
• Engeland: 2dehelft 18deeeuw
• West‐Europa en N‐Amerika: 1stehelft 19de
eeuw • Rusland and Zuid‐Europa: eind 19de‐begin 20steeeuw • Azië: na WO I • Afrika: na WO II
What do you expect ?
• Will decline of mortality go slower or faster in Africa/India in comparison to England ? • Why ?Timing is crucial: mortality declined
faster when decline started later
Na daling sterfte volgt de daling
vruchtbaarheid
• Volgt altijd na daling sterfte
Fertility declined in Europe, similarly to
mortality, but later
Decline of fertility started in most countries after 1860 Oded, 2012
Daling van de vruchtbaarheid
• Begint het eerste in Frankrijk, voor begin 19de eeuw: effect van Franse revolutie • Andere landen van West‐Europa en Noord‐ Amerika: vanaf einde 19deeeuw (Engeland eerst) • Zuid‐Europa, Rusland, Argentinië: begin 20ste eeuw • Azië: na WO II • Sub‐Saharisch Afrika: na 1990Waarom daalt vruchtbaarheid ?
• Subvraag 1: waarom was de vruchtbaarheid zo
hoog ?
• Subvraag 2: waarom daalt ze ?
Hoeveel kinderen zou je later willen ?
• https://pollev.com/gerardgovers076
Veronderstel nu even dat je in het
16de eeuwse Engeland leeft
• De kindersterfte is er erg hoog (tot 40%)
• Kinderen in een
landbouwmaatschappij=levensverzekering
–Zorgen voor kernfamilie (ouders, ook andere
verwanten)
–Onderhouden van familiekapitaal (landbouwland,
huis)
–Verklaart ook belang dat aan familie, erfrecht en
voortplanting wordt gehecht in dit soort samenlevingen
Welke kans zou je willen accepteren om in dit soort samenleving minder dan twee kinderen
over te houden ?
We can use these statistics to gain
some insight
• Binomial distribution: –Finite number of trials (n) –Outcome of each trial determined by a priori probability (p) –You can then calculate the number of successes (k)Properties of binomial distribution
)! ( ! ! ) 1 ( ) ; ; ( ) 1 ( ] [ ] [ k n k n k n p p k n p to equal is success of prob when trials n with successes k of y probabilit p n k p p np X Var np X E k n k k • You can now plot cumulative probabilities: –Calculate each invidual –Sum them for all values up to the value of k you want to consider, for a given value of n
max 1 k k k p ) ; ; (k n p pkHow does that look ?
0 0,2 0,4 0,6 0,8 1 1,2 0 1 2 3 4 5 6 7 8 9 cu mu lat iv e p rob ailit y of su rv iv al Number of children (or less) that survive 1 2 3 4 5 6 7 8 children born There is ca. 20% chance that 2 children or less will survive if you have 6 childrenEven if you have 5 children, there is a 9% change that you will end up with max. one survivor
Conclusion
• In order to be 90% sure that two children will
survive when the child mortality=40%, you will need to have no less than 7 children
Total fertility rate in Niger
However:
• The average number of children surviving will be much larger than two: consequence of the insurance principle • 7 children born will lead to (on average) 4,2 children that surviveSo, what do we need to do to get
fertility in Niger down ?
We need to reduce child mortality
“ If we want to reduce population growth we need to make sure that more children survive”Child mortality
https://goo.gl/oaylGGYes, but don’t you need
anticonception to decrease fertility ?
Not really : look at the Belgians
www.gapminder.orgOther factors are also important
Marriage age
• Age at 1st marriage
General development
• Human Development Index
Income
• Income (PPP and inflation‐corrected)
Education (women 25‐34 y)
• Education
Urbanisation (and schooling)
What about government policies ?
• Family planning counseling • Abortion • SterilisationPolitics: China vs. India
1966‐1976 Cultural Revolution 1958‐1962 Big Leap ahead 1979 One child policy 1952 Family planning program 1976 National Population plan Later‐longer‐ fewer policyGovernment policies
• Coercion rarely helps: in most societies, people consider family planning a private matter and experience government coercion as totally unacceptable • Supportive actions are another matter: policies may help to reduce birth rates faster as the desire to have less children often precedes the facts!
Samenvatting beïnvloedende factoren
Indicator Groepen landen Daling van het totale vruchtbaarheidscijfer 68-75 (promille) I II III I II III BNP/inwoner >500$ 250-500$ <250$ 630 354 302 % verstedelijking > 50 25-50 < 25 743 521 329 Kindersterfte >13,0 5,0-13,0 5,0% 238 456 783 Levensverwachting > 65j 50-65j < 50j 871 608 255 % vrouwen in de landbouw > 50 25-50 < 25 332 505 635 % geletterden > 50 25-50 < 25 716 404 232 % schoollopende mannen (°) > 50 25-50 < 25 583 424 141 %schoollopende vrouwen > 50 25-50 < 25 717 848 249 Inspanningen op gebied van
geboortebeperking sterk matig geenzwak 1157 962 214
England‐Wales vs. France
16 °/°° in 50 yr Or 0.32 °/°° yr‐1England‐Wales vs. France
18 °/°° in 160 yrs Or 0.11 °/°° yr‐1 20 °/°° in 45 yr Or 0.44 °/°° yr‐1 25 °/°° in 60 yrs Or 0.42 °/°° yr‐1 The rest of the world mainly followed the Anglo‐Saxon modelGeboortecijfers dalen gemiddeld niet
(veel) sneller in landen waar transitie
later begint: waarom niet ?
Geboortedaling is een cultureel proces
• There are now ca. 800 traffic deaths per year
in Belgium
• How many traffic deaths were there in 1970 ?
Pollev.com/gerardgovers076
Evolutie verkeersdoden in België
http://www.steunpuntverkeersveiligheid.be/sites/default/files/RA‐MOW‐2009‐013.pdf Aantal voertuigen 1977: 3.3 miljoen Aantal voertuigen 2011: 6.8 miljoen (http://statbel.fgov.be/nl/binaries/2012_Brochure%20mobilit%C3%A9%20A4%20NL%20web_tcm325‐157822.pdf) Snelheidsbeperkingen: vanaf 1973 (oliecrisis, niet verkeersveiligheid, gordelplicht vanaf 1975)Die daling kan je niet alleen
toeschrijven aan betere medische zorg
We zijn er nog niet
Dus
• Geboortedaling is voor een groot gedeelte een socio‐cultureel proces. • De transitie vereist dus dat er belangrijke socio‐culturele veranderingen plaatsvinden. • De sterftedaling is, in tegenstelling hiermee, vooral bepaald door wetenschappelijk‐ technische ontwikkelingenWhat would you expect to happen to
fertility if
• Child mortality decreases slowly due to the gradual introduction of new technology, better health care better food ? • Child mortality decreases rapidly due to the rapid introduction of all these things ?Let us see:
https://goo.gl/SCBaInWe hebben dus een basismodel: de
demografische transitie
Basic model
http://www.globalchange.umich.edu/globalchange2/current/lectures/human_pop/human_pop.html Reher, 1994: four types of transition
But with regional variations
What does this imply for population
growth
• Developed countries: –birth and death rates already somewhat reduced before the start of IR –Slow decline of mortality –Slow decline of fertility • Developing countries –Birth and death rates very high at start of IR –Sudden decline of mortality –Slow decline of fertility time Crude mor tality and f ertility ra te s The developed world time Crude mor tality and f ertility ra te sThe developing world Thus, the increase in population is not everywhere the same due
to demographic transition: much higher in the South
50 500 ‐150 ‐100 ‐50 0 50 100 150 200 250 300 japan ethiopia germany ecuador
Question
• Could there be another phase following on
phase 4 ?
Let us have a look at Japan: the past…
The near future
And the not so near future
Laten we eens even nadenken wat dit betekent voor de groei van de wereldbevolking • Gaat die blijven groeien ? • Gaat de groeisnelheid contant blijven ?
Dus….
• Bevolkingsexplosie is gevolg van demografische transitie • Is een tijdelijk fenomeen • We zitten nu in de eindfaseGross fertility 2005‐2010
http://upload.wikimedia.org/wikipedia/commons/7/78/Fertility_rate_world_map_2.png
Is the next statement true ?
We need birth control to stop
overpopulation because…
• There are ever more children (especially in
poor countries)
• They will again have more children !
• Etc….
Neen
http://www.census.gov/ipc/www/idb/worldgrgraph.html
In somewhat more detail:
Globally, remaining growth is about
filling up the pyramid
Well…the number of children on the
planet is already over the top
UNDP World population prospects 2010 595 000 600 000 605 000 610 000 615 000 620 000 625 000 630 000 635 000 640 000 645 000 650 000 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 2110 UNDP prediction of number of children < 5yr kind < 5
UNDP, World Population prospects data 2010
Verdere groei van de wereldbevolking
• Niet meer te wijten aan stijgend kinderaantal • Volledig te wijten aan verhoging van de levensverwachtingHow far will aging go ?
Life expectation continues to rise…
And there are optimists…
But there is a catch
Age of oldest person in the world at
death vs time
108 110 112 114 116 118 120 122 12424/jan/41 3/okt/54 11/jun/68 18/feb/82 28/okt/95 6/jul/09 15/mrt/23
Series1 Data from wikipedia Maximum age of survivors moves hardly, but much more people live up to a ‘decent’ age https://www.env.go.jp/en/wpaper/1995/eae240000000000.html
Despite this optimism we need to be
careful
• We cannot do anything but rejoice about the fact that almost everybody in the world now lives to a decent age (and we do not want to do anything about that) • Thus: only possible control on population growth is through control of fertilityHoe zorgen we voor controle op groei
?
• Niet door te panikeren
• Niet door stringente geboorteprogramma’s
• Wel door verder terugdringen kindersterfte
• Wel door verschaffen onderwijs, vooral aan
jonge vrouwen
Fertility decline is difficult to predict
And slight varitions in TFR have a
strong impact on total population
Gerland et al., Science, 2013Recently, projections for Africa have been
revised upward: perhaps 4 billion Africans
in 2100
Gerland et al., 2013, ScienceBut we do now that some factors have
a tremendous effect on TFR
• Child mortality • EducationMortality decline
(Child) mortality has declined to near‐minimum levels in mlany countries over the last 25 yearsMortality decline
(Child) mortality has also declined in Africa, but will decline further, less room for decline in other regionsBesides child mortality education (of
women) is of tremendous importance
Key factor is education (Lutz et al., 2011)
GET: global education trend CER: constant enrrollment rate CEN: constant enrollment numbers FT: fast track (Singapore and S‐KoreaComparing different SSP’s
Lutz et al., 2014 SSP=shared socio‐economic pathwayFor each SSP
• Try to predict effects on life expectancy and TFR using known effects of : –Education –Wealth –Etc….Results show that very different
developments are possible
This is also true for individual countries
Main lesson
• There is nothing inevitable about uncontrolled population growth • It all depends on our actions as a global community • If we invest in schooling and medical aidIs bevolkingsexplosie een kans ?
Waar is het aantal actieven het grootst
t.o.v. het aantal ouderen en jongeren ?
UNDP World population prospects 2010 Bloom and Canning, 2004Wat betekent dat voor economische
groei ?
An and Jeon, 2006Demography also explains within
country variations in growth
Growth rate between 2000 and 2010 of different states in the US vs growth rate in 60+ population over same period (Maestas et al., 2016
Afrika is een groeicontinent
En dit krijgen we in Japan….
But make no mistake:
• It is not the number of people that counts • It is how they are skilled. It is not the duration of schooling but the level achieved that is importantConclusies
• Bevolkingsexplosie is soms problematisch • Maar : er komt een einde aan • Het komt erop aan om ervoor te zorgen dat ontwikkelingslanden kunnen profiteren van de kansen die de demografische transitie biedt op economische ontwikkeling • Hoe doen we dat ? Investeer in onderwijs en vooral in kwaliteitsvol onderwijsConclusie
• Volwassen samenlevingen hebben het omgekeerde probleem: vergrijzing verhindert economische groei • Get used to it ! • But remember: ‘Prediction is very difficult, especially when it is about the future’ (N. Bohr)www.gapminder.org
• Website with lots of data
• Allows us to visualise evolutions
But watch out for surprises
• “Prediction is very difficult, especially if it's
about the future”, (N. Bohr)
What would you think would be the effect of the Fukushima disaster ? http://media.npr.org/assets/img/2011/04/12/japan‐quake‐nuclear‐disaster‐accident‐ files_6929693_custom‐365fa520bb48c84bd64f8f48d69e9a4f6e8f35ec‐s51.jpg
Oops !
http://www.indexmundi.com/g/g.aspx?v=31&c=ja&l=enHoe is die transitie tot stand gekomen
?
Why industrialisation ?
• Basic change : use of fossil fuels to produce
mechanical energy
–Total annual useful energy production of a grown man: 0.075*10*300= ca. 225 kWh per year or 225*1000*3600=810Mj (1 kWh=1000*3600 Ws=3.6Mj), or ca. 2 MJ per day –1 kg of wood: 15 MJ –1 kg of glucose : 20 MJ –1 kg of coal: 30 MJ –1 kg of diesel: 50 MJ –1 kg of hydrogen: ca. 143 MJ –1 Kg of Li‐ion battery: 0.72 MJ –1 kg of Uranium: 79.5E6 MJ
Industrialisation causes a chain
reaction of changes leading to a
FUNDAMENTALLY different society
Energy Workers Socialis m Trainin g Health care Reduced religious influenc e Capital Migrati on Urbanisation State organis ation Agricul ture Scie nce nu trit ionWhat hebben we geleerd ?
• We hebben dikwijls weinig kennis van een
probleem
• Weten=meten: opinies en beslissingen nemen
op basis van feiten is een geode zaak
Waarom ? Kindersterfte daalt
Waarom daalt kindersterfte ?
• Verbetering medische zorg
–Betere technieken
–Goedkoperen technieken
• Maar ook…..
A summary…
Het aantal jonge kinderen stijgt dan
ook niet meer
595 000 600 000 605 000 610 000 615 000 620 000 625 000 630 000 635 000 640 000 645 000 650 000 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 2110 UNDP prediction of number of children kind < 5
UNDP, World Population prospects data 2010
Groei van de wereldbevolking
• Die is er vooral omdat we met zijn allen ouder
Well…the number of children on the
planet is already over the top
UNDP World population prospects 2010