Science Questions

What is the maximum human population?

Mon, 16th May 2016

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MLG asked:

Regarding "Ideal Human Population", no one seems to really answer the question, taking into consideration the land needed for houses, stores, roads, animals that need forests to live, water (lakes, ponds) forests for lumber to build these homes, stores etc. what about the farmland needed to raise the cattle, pigs, chickens we need for survival. Land for factories....get my point. All they talk about is land for growing grains. 15 years ago economists and scientist estimated the max human population to be 4 billion...


We are in big trouble, we are destroying the earth more everyday, and we are too egotistical, and stupid to realize it and do something to correct it. Just requiring two children per couple would start reducing the problem. You want more than that... adopt...


Howard - The background of this is that we expect the global population is going to increase by 2-3 billion over the next 50-100 years or so, but we then predict it will level out to some extent. Crowd WalkingAnd as the questioner hints in their original question, we also expect we’re going to see population’s increasingly becoming urbanised, part of city dwellers and they’re also going to want to have higher aspirations to lifestyle. So they going to want to increase their meat consumption and that is also not a very effective use of resources.

And then we’ve got planet change that we’ve been hearing about so we’re going to get increased climatic extreme, floods and drought. So the question is, can we sustain the population that we are predicted to see?

Chris - Which is what?

Howard - We’re currently heading towards 10 billion people. So we’re about 6-7 billion at the moment and we’re likely to head towards 10 by the end of this century.

Chris - People say we’re consuming resources at the moment at the rate of two planet earths, not one. So, if you increase our numbers by another 30-50%, which is what that number you’ve just suggested is, that means we’ll be up to three planet earths per person equivalent per year. That’s totally unsustainable, surely?

Howard - It is dangerously unsustainable and that increases the threat upon our natural vegetation because there will be a demand to try to convert more land area into agricultural productive land, so it’s a real threat all the way round. But then you can come back on us and say, well why don’t we control the amount of food we waste? Up to 40 or 60% of the food that is bought in America and in Europe is just thrown away, it’s not consumed. Why don’t we learn to redistribute that food better?

Chris - Isn’t that a short term solution though, Howard? Because if I feed more people, I’ll get more people and we’ll end up at the natural point where we’ve still got a population crisis albeit with a higher number of people ultimately anyway.

Howard - Well, coupled with this increasing population, we expect that there be increased education. There’s going to be an increased awareness that you no longer need to have a huge family to support you in your dotage, as it were, and that actually small families are sustainable and they are realistic. So what we actually need to focus on is education and particularly empowerment of women. This is really important on a world scale to try to get cultural understanding that a huge family is not necessary.

Chris - You’re a plant scientist though. I suspect you would love to see a solution to this problem lie with plants but there have been some people who’ve suggested that, in fact, if the entire world went vegetarian, this would immediately cut our carbon dioxide output by quite a significant amount. Because, if you look at the average westerner, we probably eat our own body weight in meat each year and, if you look at the rearing cycle for meat, we need about three years worth of supply. So, therefore, there’s probably three times as much weight of animals as there is humans so you could immediately translate that into a very dramatic reduction if we all just stopped eating meat but, would we be healthy?

Howard - Yes, indeed. One small step we might care to take is to go vegetarian one or two days a week and this would start to change us to move towards a more sustainable diet, it would be better for our health as well.

Chris - The other possibility is in-vitro meat, isn’t it? We’ve heard in the last couple of years we’ve had the in-vitro burger being made where people grow cells in a dish and make muscle artificially. Apparently, it doesn’t taste too good though!

Howard - It looks pretty horrendous as well!

Chris - Okay, maybe I’ll give that one a miss then!


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Maximum human population...


Just look at all the chaos that happened once Eve showed up!!!

I firmly believe in the policy of one child per person, two per couple, which if strongly enforced would give a gradual population reduction.  In the USA there are many tax and other incentives for large families.  Tax deductions are fine for the 1-2 children, but after that, there should be severe tax increases (starting with future births, and perhaps immigrants).

At this point, we certainly are living beyond our means, and the world is suffering. 

Perhaps one should ask if the world could support 7 billion Africans living in slums...  vs 7 billion "Americans".

I'm not sure what the answer (in excess of ONE) would be for human population.  A gradual reduction to 3 or 4 billion would be a good start.  Doing so should cut greenhouse gases in half, perhaps allow growing more fuel crops, and digging up less fossil fuels.  And, reduce the human pressure on the world's water resources.

Many religions consider humans as the "good shepherds" of the planet...  but are doing a poor job at caring for anything but themselves. CliffordK, Thu, 25th Sep 2014

Not sure about the rest of the world, but the UK could be indefinitely sustainable at well above the present quality of life with about 10 - 20% of the present population. There's no problem achieving it: if we pay every woman £500 every 6 months if she isn't pregnant, and abolish all child support payments, the birthrate would surely fall very quickly.

At 1 child per woman we would reach the required level within 80 years without anyone doing anything. The interesting consequence is that everyone's quality of life would improve from the outset because the working fraction of the population would increase from the present 55% to well over 60% and we'd be spending less on child health and education, so pensions would increase or we could retire earlier.

Why won't it happen? Because current economic theory is all based on growth of the industrial sector (which means you need ever more consumers to buy the stuff) and 30% of the UK's GNP consists of selling houses to each other, which you can only do at a profit if there is a shortage of houses (i.e. too many people).

What is required is a good sales pitch. How about this: "You can have £1000 a year for doing nothing. You can retire earlier, with a bigger pension. Your children and grandchildren can have all the space and material goods they could possibly need with no dependence on fossil fuels or nuclear power and no need to import food. No congestion, no overcrowding, less pollution - but you and your descendants will still be able to drive and fly anywhere, any time. For ever. All you have to do is...nothing!" Sounds good to me. alancalverd, Thu, 25th Sep 2014

Those reductions are pretty drastic.

Are you sure about the "working fraction"?  I suppose if you consider both the under 20 and over 70 populations, it might even out.  However, the retirement group would cause a significant burden to society.

A strict 1-2 child limit, as well as limiting immigration from any nation that doesn't have its population under control would cause a more gradual decrease due to the number of individuals or couples that don't have their 1 or 2 children respectively.

However, perhaps one should consider rapid depopulation as an answer to our heavy fossil fuel dependence before we are either limited by resources, or atmospheric change. CliffordK, Sat, 27th Sep 2014

I can't upload the graphs but the model is simple. Divide the population in to "under 20", "working fraction" and "60 - 100" and assume that we die off linearly from 60 to 100. Then if we have a simplfied stable replacement (2 children per female aged 20 - 60)  we have 25%, 50% and 25% in each cohort. 

The working fraction has to support the pensioners and the children.

Now reduce the birthrate to 1 instead of 2. After say 10 years the child cohort obviously contains rather less than 25% of the whole population, so there is more money available to support the pensioners (and fewer working hours lost to maternity).

After 20 years the number of working people decreases but so also does the number of children (remember you only reproduce, and only once, after age 20 in this model), and after 60 years the number of pensioners begins to decrease too. In fact the working fraction wobbles a bit over time but never falls below 50%. More to the point, everyone is increasingly wealthy because there are continuously fewer people living on the same amount of natural resources. 

On this model the UK population falls from 65,000,000 to just over 12,000,000 in 110 years, with personal wealth and comfort increasing throughout the period. Far from drastic, the process requires nobody to do anything except enjoy the extra space and increased pension. alancalverd, Sat, 27th Sep 2014

and wait for and an overpopulated neighbouring country to invade to utilize UK resources , analogous to "Lebensraum".
(smaller population has smaller armed-forces ). RD, Sat, 27th Sep 2014

"Invadeability" is not related to population density or individual wealth: Canada, USA and Australia all have a tiny population per unit area or per mile of coastline, vastly more per capita resources than anywhere else, and have only ever been invaded by Britain. Nobody in their right mind would have voted for Scottish independence if they thought that a third of the British mainland could not be defended by a twelfth of the population (with no navy or air force). Ireland has pretty much the same population density as Scotland, a comparable standard of living to the UK, has not been invaded (except by Britain) since the Romans left, and has retained political neutrality south of the border for nearly 100 years.

Our neighbouring countries (France, Holland, Belgium, Ireland, Germany, Denmark, Norway, Iceland) are neither overpopulated nor starving, and are quite likely to follow the UK's lead in population reduction anyway: the principle applies anywhere, and can be put into action most easily in a broadly socialist democracy.The prewar population density of Poland was similar to that of Germany and per capita resources were far less: lebensraum isn't based on rationality.  alancalverd, Sat, 27th Sep 2014

"Invadeability" is related to the total population in a territory. If population was continuously decreased there must come a cut-off point at which it cannot defend itself from invasion.

The invaders don't necessary have to be neighbouring , it's just less of a commute if they are. In the fullness of time China might fancy a new colony , ( they've already invaded the the UK high-street :¬)

IMO Nobody in their right mind did.

My main point was history has shown invasions of under-defended lands are standard-practice, and that perspective was not included in your plan to reduce the UK population to 1/4 of its current value in a century. Supposedly Britain only had a population of about a million in 1000AD,
if it ever went that low again Britain would become a colony of another European country to exploit its resources. RD, Sun, 28th Sep 2014

"Invadeability" is related to the total population in a territory. If population was continuously decreased there must come a cut-off point at which it cannot defend itself from invasion. but nobody is going to invade a territory for the fun of it - there has to be a profit motive. When was your house last invaded? Very few people in it, I suspect, but unless you have a gold mine or an oil well in your back yard, no point in even trying. Massive civil disruption in Kenya and Sudan, fairly small population, but no Western invasion, air strikes or military advisers, because there's no oil and very little food. Mainland Britain no longer has any exportable natural resources since Thatcher destroyed the coal mines. As you say, China now sees the UK as a profit center (since the EU destroyed our manufacturing industry). You don't invade your customers, you bleed them. 

IMO Nobody in their right mind did. When I say things like that my Scottish friends accusse me of racism. if we had any - see above - and if they needed any - they'd be better off following my example and reducing their population to the point where they were not dependent on the charity of Islam to maintain their standard of living. As it is, we are already a colony of Germany, China and Saudi Arabia: they take our money without having to put up with our weather. alancalverd, Sun, 28th Sep 2014

A huge population is certainly handy when defending yourself against an aggressor, as Hitler discovered when he invaded Russia and Britain discovered in the Zulu wars. But, it does not necessarily discourage an invader to give it a go.

But I think the question was more directed at whether Earth has a limit to the number of humans it can sustain.

The current population of 7.2bn could be fed easily, IF, and its a BIG 'IF', the distribution of food and wealth was more even.

In the UK there are families with both parents working who struggle to be able to afford to buy food enough even for a family of 4, while there are others who enjoy an annual wage packet equal to that poor family's entire lifetime's earnings. In fact there are some who's annual income may be 5, 6 or even 10 times that of the average lifetime income.

Note I say 'income', not 'earnings', since many of these super-rich do little or nothing to 'earn' their income.

Financially, the world needs to equalise remuneration and cost-of-living. (ARE YOU LISTENING EU COMMISIONERS???)

But there is another problem which we face when trying to sustain the population, and that is population distribution. There are almost 8.5m people live in London and roughly the same in New York. These cities cannot produce or provide the food, water, oxygen, energy and raw materials required by those who live there. These cities excerpt huge pressures upon vast swathes of land, many, many times greater than the area they cover, to provide for them. They also cost dearly when it comes to getting the produce from producer to consumer. This puts inordinately high costs on providing for the populous.

And if you think that's bad, Shanghai, Karachi and Beijing all have populations' in excess of 20m, while Dhaka, with more than 12m, has a density of almost 40 people to the Km2. London has just 5 and NY, 10.

Then, of course, there are those who live in regions which simply cannot sustain even fairly small populations because the climate or geological situation is simply not favourable to agriculture and may struggle to provide anything natural in the way of food.

I think our problem is that we have become too interdependent on each other. I seriously doubt many would take too kindly to reverting to the old days when small villages provided for themselves, so we seriously reduce the sustainable population capacity of the world.

If you lived in some parts of the world, you could be forgiven for thinking that we have already passed the limit. In others, with more than 20% of food going to waste, you might think we have a long way to go to the limit.

Don_1, Tue, 21st Oct 2014

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