Monday, December 29, 2008

How Many People Can the Earth Support... Really?

This is not simply a question of how many people can be crammed onto the dry surface of the planet. For example, it is easy to calculate (as I indicate below) that if the present number of 6.7 billion of us were each allowed an area of one square metre, we would collectively occupy just 6,700 square kilometres, or an area enclosed within a square about 50 miles by 50 miles, which would fit with spare room within a county the size of Yorkshire.

This is a comically naive piece of arithmetic, but not much more so than many sums I have seen done as to how many might exist on Earth given a daily diet of, say, 2,500 Calories, in which case a figure of around 12 billion can be deduced. So, whoopee, we may well pass that WHO estimate of 9 billion by 2050 and maybe get to 12 billion by the end of the century. Beyond simple issues of how much food we might need, and water for that matter, along with fertilizers and other material resources to build shelters and clothe ourselves, are more complex but equally fundamental questions centred around quality of life and human dignity.

So, what do we mean by living and what standards of it might be considered acceptable? Would we in the West want to “fall” materially to the standards, say, of western Africa? Or, is the economic dream more wishful, to raise the living standards of the majority world to those of the West? The answer is really the proverbial elephant in the room. If the whole existing number of people on earth lived at the standard of an average American (if there is really an average anybody), it is said we would need five planets worth of resources.

It’s about 3.5 planets for a typical European (an even less average scenario), and four earths for that many Australians. Simply put, the latter prospect is not viable, and in the longer run neither is it for Americans, Europeans or Australians, let alone the whole world. Modern, chemically fertilized, mechanised farming is very successful. We can also kill-off pests with synthetic pesticides, and so crop-yields on Western farms are the best on earth, but they are unlikely to be sustainable.

So, in the absence of plenty of cheap oil and natural gas, what is the upper limit of population, or conversely, the lower limit of material quality. Well, O.K., let’s say that we are all allowed that 2,500 calories every day.

6.7 x 10^9 people x 2500 Cals/day. 1 Cal = 1000 cals, so 1 cal = 4180 J (4.18 J/cal).
So they would all eat, 6.7 x 10^9 x 2500 x 4180 x 365 = 2.56 x 10^19 J/year.

So, what might be grown in total?
We have 15 x 10^6 km^2 of arable land for crops. If we assume that 2 tonnes of edible food can be grown (from maybe 5 tonnes of crops mass) per hectare/year, and that this is in the form of simple sugars, i.e. C6H12O6, with an energy content of 2800 kJ/mol, we get:

2 x 10^6 g/year/180g/mol x 2800 x 1000 J/mol = 3.11 x 10^10 J/ha/year. And converting 1 km^2 = 100 ha, that’s grown on 15 x 10^6 x 100 ha of land, so we have:
1.5 x 10^9 ha x 3.11 x 10^10 = 4.67 x 10^19 J/year.

Now this might be seen as good news in that we can produce around 80% more food energy than is consumed by the present 6.7 billion humans, leading to the conclusion that the earth can support around 12 billion of us, so as I said, maybe we can meet the WHO targets of billion by 2050 and 12 billion by 2100.

But, we would all be living on the proverbial “bowl of rice a day” [(2500 x 4180)/(2800 x 1000) = 3.7 mol = 672 grams].

(This ignores growing any food for animals, that you could get these crop yields without artificial fertilizers and pesticides and there would of course be no crops grown for biofuels).

I have mentioned before a Hubbert type analysis that can be applied to human population growth which is already slowing down. This predicts that in 2024 there will be a maximum at 7.1 billion people (not many more than the 6.7 billion now) after which there will be a decline to 2.5 billion by 2100. I would not be at all surprised because resources to support population are limited.

Now that 2.5 billion at the end of the century may all be living equally and equitably on one planet's worth of resources, or more likely there will be even more poverty all over the world but with a smaller differential between the developing and industrialized nations, if either category are that by then. The level of poverty can only fall so far, because the lower limit of destitution is death.

I think many in the West particularly would sooner die than return to the conditions of a pre-industrialized society, even it that could be relatively well-provided for by agriculture.


Yorkshireminer said...

The Question Chris is how many people will the world support.

Professor Chris Rhodes said...

Happy New Year Dave!

Now that is the question isn't it?

I don't think it's going to be 9 or 12 billion anyway!


Yorkshireminer said...

How very remiss of me Chris not to wish you a Happy new year. What History shows you is that when a society reaches a certain carrying capacity for the level of technology I am thinking here of Medieval Europe. Before the black death there had been many plagues that had infected different areas of Europe coming back at regular 30-40 year intervals. When the Black Death stuck Europe in 1339 or there about Europe had reached the highest population density figures ever. What had been happening was that Europe had developed its trade routes far more extensively. There were far more trade and towns had grown in size. The extensive and more heavily used trade routes allowed the disease to be transmitted far more quickly and the larger more unsanitary towns allowed for a higher percentage of deaths. It took only about 18 months to spread from Southern Italy to the North Cape of Norway. 30% deaths in a small area as a total of Europe is much smaller than 30% deaths of all of Europe. All energy used in Europe was renewable at that time.

Which of the four horsemen gets into the saddle this time I wouldn't like to say but I think all four will have a good chance of doing a hell of a lot of damage. Modern agriculture is nothing more than a sophisticated way of turning oil into food. When the oil runs out the food runs out. War will most likely be a certainty, We are certainly heading in that direction in the Middle East, to put it politely, for religious ideological reason. When a unreasoning irresistible force meets an unreasoning immovable object something has to give, that is without counting in resource wars. Disease of course goes without saying. Take a pathogen with a long incubation period time, say a month, that is infectious, and Similar too the Spanish Flue and it can infect the world in a couple of weeks with the world wide transport system we have now. I suspect that a 10% casualty rate in a country like Britain would quickly bring it too its knees. That is without crop diseases there is a form of wheat rust working its way across Africa at the moment that is forcing the U.N. To ask for more money for its food program. Imagine what would happen if it was Rice rust. We all know what happened too the Irish potato crop when it failed five years in succession. Imagine millions of Bangladeshis moving into Indian Bengal and Assam who are suffering from the same curse. Bangladesh has a population of 160 million in a area the size of West Germany. The Irish could at least move to the U.K. And America. The inertia of such a mass movement would certainly destabilize India. Pestilence well that is a forgone conclusion when oil runs out as most of our pesticides are made from oil. We have built a world economy on finite resource, oil. It is a pyramid scheme that when it collapses will topple like a house of cards. Europe in the 14th century had a least plenty of food, and its energy resources were at least renewable. This time it could be a world collapse and coming out of it with little food and no real energy resources it could add to the downward spiral. Where population, bottoms out nobody can guess, but I would expect more than 30% which was the estimated percentage of the Great plague, and we mustn't forget that when a population reaches a certain point such as in the over fishing of the Great Banks for cod the cod population virtually collapsed. I don't think anybody can predict what the correct figures will be , but there seems to me too many positive feed back loops in this pyramid system of ours for the world to get off lightly. The best guess estimates will be by statisticians who use loaded dice.

Deep regards


Professor Chris Rhodes said...

What you say is spot-on, Dave, and I find myself thinking that it might be around 3 billion as a final number, say by the end of the century.

You are right about oil, and that it has been sand into which the foundations of the modern world have been sunk.

I smile in a grim way when I hear people talk about technology and advanced computing, robotics, etc. - the kind of thing that used to be on Tomorrow's World, if you used to watch that back in Blighty, but of course all such possibilities, whether they actually manifested or not, relied on cheap oil.

Without that there won't even be food, especially in the industrialised nations... so all else is pie in the sky (maybe the only "pie" to be had!).

It is almost as though we are all "fiddling" while the foundations of civilisation collapse.

Deep regards,


Anonymous said...

These calculations are amazingly simplistic.

For one, they don't count as usuable for food production ANY underground area, although given a way of introducing enough light quite a bit caves,tunnels, etc near the surface of the earth might be used to grow farms.

Second assumption: the oceans are not a food source of any type.

Third assumption: No cheap energy, not even solar. This whole blog is to explore the possibilities of energy production, both positive and negative as oil reaches peak production.

Fourth assumption: No soil creation of any type via any process, man-made or natural.

Sorry, but I'm not buying.


Professor Chris Rhodes said...

Hi Clarence, it's been a while...

right, now these are the kind of sums you see everywhere and they are as I note comically naive. That's my point.

However, when Prof. Pimental talks about 2 billion he has a point and he emphasises the aspect of !quality of life" not just numbers.

Do you think that we shoul;d just carry-on cramming more and more of us onto the planet or maybe some energy efficiency strategy might be prudent?

Do you really think we can grow much "underground"... how, on any significant scale in cave entrances etc., unless we get into the "hollow Earth" notion, which some people do believe in, so I'm not knocking them.

The oceans of course, we are not only talking about fish etc., but there are serious ideas about growing microalgae as food, to provide more than the restrictions of land=-based agriculture.

What are these energy-inputs that I have ignored? However, there is a good point here, that the 2 billion or so are what we might expect to be supported in the absence of additional energy inputs.

The oil problem - not peak oil, but gap oil - peak oil will just make the matter worse - is real and this will impact harshly and rapidly on agriculture, and also growing and harvesting seaweed etc and fishing for that matter. So, how do we get around that one in a hurry?

Soil creation? Now that is a good point. The quality of topsoil has become extremely poor and it will take nature millennia to improve it. There are strategies e.g. "remineralize the earth" which involved grinding huge amounts of rock into dust to furnish a fertilizer for soil and also "biochar" sometimes called Terra Pretta, which is a great idea, especially since both approaches could seqiester CO2 from the atmosphere, but the amount of effort, time and energy to install them would be gargantuan and lengthly.

So, I haven't thrown my hands up yet Clarence, but keeping up the advance in human numbers will not be easy, certainly to 9 or 12 billion.


Anonymous said...

Hi, Chris:

I'll put up a reply tonight.

I do want to say I've been following the blog when I can, and I don't disagree with you quite as much as my post might have led you to think.


Professor Chris Rhodes said...

Hi Clarence,

it's a difficult question but my point is that however many of us live in "Spaceship earth", there must be quality of life for all.

I think the Hubbert analysis is probably an indication of population in the absence of further inputs of energy, regenerative agriculture, terra pretta, sea-borne agriculture, and so there is hope that the condition can be improved on.

Best regards,


Anonymous said...

This is my very uneducated view of the situation. I have no deep understanding of any of this.
Regardless of how much space we have underground to grow crop etc - only so much light from the sun (energy from the sun) which is the main ingredient to growing any form of crop, hits the earth. So once the oil/fossil fuels have run out the earth would only be able to support (via growing crops completely naturally) a fraction of todays population.

Professor Chris Rhodes said...

Hi Rob,

I looked at this at a while back and concluded that at a reasonable level of solar irradiance, you could get around 250 tonnes of biomass reckoned in terms of sugar per hectare.

Not all crops are as good as this so it depends on where you are and what the level of sunlight is. Here I have taken actual measured crop yields and very simply reckoned them up to feeding a large global population.

I agree that in the limit photosynthesis is the deciding factor but below that limit it depends on crop yields.

Now most farming especially in the West is of the industiralized kind, so it deonds entirely on oil-based fuels to put into tractoprs and cobine harvesters etc., and natural gas to make nitrogenous fertilizers. For that matter too, oil is used to mine phosphate etc. also for fertilizer.

Thus when we begin to lack cheap plentiful oil and gas huge impacts will be imposed on farming.

For this reason, I am becoming interested in methods of regenerative agriculture and permaculture which are per se less demanding in these fossil resources. I have written some articles about this kind of ting more recently.



Anonymous said...

We're fucked.

Professor Chris Rhodes said...

Yep, I think so too!