Horizon: Attenborough on Population Growth

He's right hainey.

If my grandparents were still alive then there would be more people in my family. Simples.

Graham you like Excel go on you know you wnat to

i thought about it. I did. But I'm lying in bed (off work with the shits) so I really can't be bothered 🙂

Ok, on the assumption that everyone lives forever then i admit population would increase.

The general concept that you are missing is that it does not matter how old someone lives for, if the population is not replacing itself then populations levels will decrease.

As graham said just imagine some people who are dead had lived longer and were alivve now …are there more of us or less? They still die and the population would stioll stop rising eventually but increase in the short run 20 -30 years ish [at a guess]

Ps Get well soon – That is to Graham…. Hainey is beyond hope I fear 😉

Was that a back track Junkyard? So you are actually saying that population would decrease?

Ok, glad you got that one sorted out. 😉

Ok, on the assumption that everyone lives forever then i admit population would increase.

It doesn't need that qualifier for short term growth. If average lifespan increases from say 50 to 60 years then in 60 years time you'll have an extra ten years worth of people to feed.

http://www.guardian.co.uk/commentisfree/2008/apr/15/food.biofuels

Some agree with George Monbiot, some don't, but he usually has a point.

hainey can you actually count?
If we are all living longer – which does seem to be the case IIRC- and parts of Africa have a current life expectancy of 40 at present [some parts of the west currently 80 and rising still].
What in terms of numbers will the effect be of people not dieing on poulation? INCREASE OR DECREASE? It is not particularily hard to work out.

Junkyard, you still not got it? Seriously? 🙄

If less people are being born than are dieing, then population decreases. Its not hard to figure out. It doesn't matter if people live longer or shorter, everyone still dies.

It doesn't matter if people live longer or shorter

so if we all live to be 100 years old or all die at 35 the population in both those scenarios is the same/unaffected. Is one higher or lower?

If everyone lives to 100 or if everyone lives to 200 or if everyone lives to be 1000 years old, if the birth rate is less than the death rate then population goes down.

OMFG
So in hainey world/maths if everyone alive today [and all their off spring]live to be a 1000 as long as we only have two children the population levels fall…. wow what a powerful grasp of the subject and maths you have.
I cannot believe you are saying this

The important thing is the transition. Lifespans are currently INCREASING hence they are contributing to population growth.

If our generation all lived to be 150 then the population size would explode, because that's a huge increase over the current normal lifespan.

BUT if we get to a stage where everyone lives to 150, and has done for over 150 years, and no matter what we do we can't improve on that THEN it will stop contributing.

Oh and this quote is true:

if the birth rate is less than the death rate then population goes down

but is a some what different argument to your original points:

If everyone still dies, and every couple has 2 kids (i.e replaces themselves, then you have a population stability. If out of those 2 kids for every couple some are killed due to accident, disease, war, natural disaster etc etc, then population will decrease.
…
An aging population will just mean a shift in average age.

Since as we have explained, you don't have "population stability" with an ageing population.

Oh boy, this Hainey Vs Junkyard is becoming a classic!

If I understood Hainey's point, then he is correct: if every two people only ever have two children then the population cannot increase as long as some people die (accidents, etc.) before they breed, no matter how long they live, IN THE LONG TERM.

This is where Graham's point comes in: Lifespans increasing and leading to a larger population will become inconsequential when the ever-increasing lifespan advances reach an inevitable maximum.

Right…?

Yes, where Junkyard is going wrong and seemingly knows it but is arguing his point until he is blue in the face is that he is assuming that we all live to be a million years old.

It is IMPOSSIBLE for the population to keep increasing if the birth rate is less than the death rate! Yes, if suddenly through and advancement is science the average age suddenly jumped from 80 to 85 then for that 5 years we would have a surge in population as, for 5 years essentially no one would be dieing.

Junkyards grasp of basic maths is quite awful really.

In fact, the more this conversation goes on the more i think Junkyard is actually a troll. Surely no one is THAT stupid? Junkyard i had to say i told you so on the global warming debate, just admit you are wrong before you are embarrassed again! LOL. 😉

To put a few figures on this:

Life Expactancy
Bronze age: 18
Classical Rome: 20-30
Early 20th century: 30-45
Current: 66.5

The distribution also indicates that some countries still have a lot if catching up to do.
It's only 39.5 years in Swaziland, but 81 in Japan.

It is IMPOSSIBLE for the population to keep increasing if the birth rate is less than the death rate! Yes, if suddenly through and advancement is science the average age suddenly jumped from 80 to 85 then for that 5 years we would have a surge in population as, for 5 years essentially no one would be dieing.

Ok so it is impossible but then you give an example 🙄

If everyone lives to 100 or if everyone lives to 200 or if
everyone lives to be 1000 years old, if the birth rate is less than the death rate then population goes down.

Is this true ?

Graham…Excel you know you want to 😉
I agree with all Graham has said so far.

Ok so it is impossible but then you give an example

Sheesh, this has gotta be prime-time trollage! (Why am I feeding it???)

The population increases for five years (ultra, ultra simplistic example as obviously life-expectancy doesn't jump from 80 to 85 overnight) but then it can only decrease.

What is so hard to understand? More people are dying than are being born.

Do you really need an excel sheet to demonstrate this??

Nice post Graham.

I reckon I'm in the right industry then. I'm not against organic food production as it is a niche for farmers to make a bit more cash, but I'm afraid it will eventually have to be knocked on the head in favour of feeding the 9 billion by 2050. There is less and less land per head as the population grows so we have to increase yields through breeding better varieties and through better crop protection (yes – pesticides). Before I get flak about nasty chemicals (why don't you go have some Nurofen and a coffee), the other option is transgenesis (or GM as we would know it). Which one do you like best?

The other option for the time being is to become a vegetarian. It takes approximately 6kg of grain to make 1kg of meat. There are about 12 loaves of bread there. Should reduce green house gas emissions a bit too.

Certainly gets us thinking!

Erm.. does it help if I point out that

a) population growth rate does indeed = birth rate / death rate

but also

b) an increase in life expectancy means a reduced death rate, i.e., it does contribute to population growth

(where birth rate = number of live births per 1000 population per year, death rate = number of deaths per 1000 population per year)

is everyone happy now?

Erm.. does it help if I point out …

Sorry, but no, not really.

I had hoped that we'd already established that death rate is reduced ONLY UNTIL the life expectancy no longer increases.

THEREFORE…

the population growth is only TEMPORARY.

Is everyone happy NOW? 😉

Of course it's temporary, assuming life expectancy doesn't go on increasing for ever. When life expectancy stops rising, you have a new equilibrium.

…and at that point population begins to decrease if couples only have two children.

May be wrong, but don't you need a defined time span? for example 1000 years. If everybody changed the variables but took the results over 1000yrs (the control measure common to all calcs). Then they would be directly comparable eg.

If life expectancy stays the same and birth rate increases by X% yr on year then after 1000 yrs the pop. will be X

or

If life expectancy increases by x% over x yrs and birth decreases by x% then after 1000yrs the pop. will be X.

May have been said before or may be wrong so please don't flame me! 😀

Finding this discussion quite interesting!

You're kinda correct, JP, but there are too many variables in your examples to be able to say that the population would be the same.

I think….

Oh crapola, now I'm properly confused.

Junkyard is right, with the qualifiers that GrahamS has given. Hainey is also right over the slightly longer term, for the same reasons that GrahamS has given.

What's the problem?

Hainey is right in the FOREVER term, once we're past the short term.

(where the short term is the period in which life expectancy is increasing)

And yeah, what IS the problem? Once life expectancy stops increasing the population can ONLY decrease if each couple only has two children.

whatever, if we carry on like this, there'll be 9billion of us in a few decades time.

that's a lot of people.

it'll be hell trying to find a parking space at waitrose on a saturday morning…