[Keith]

Keith asked the Naked Scientists:
   
Dear Naked Scientists,

9000 people are born every 45 minutes (approx).

I was watching a programme with Sir David Attenborough talking about increases in the population  - they suggested that the planet could only sustain around 15 billion people.

We currently have almost 9 billion living on the Earth, so if there are 9000 people born every 45 minutes (roughly 250 000  per day) how long will it be untill we find it hard (or harder) to sustain our world population?

Keith

What do you think?

[Don_1]

It rather depends on the distribution of the population.

A wide spread population living on local produce is more sustainable than the current situation where millions are crammed into relatively small areas and depend on produce imported from 100's and 1000's of miles away.

It makes no sense to import apples into the UK from Sth Africa, yet we do it.

[Mazurka]

I thought the thrust of the programme was that we don't actually know, but best estimates suggest if we all lived as frugally as sub saharan africans we could sustain 15 billion, but if all we lived with the profligacy of the west then 3 billion might be too many.

Ultimately it is a question of resources - energy, water & agricultural land.

[Karsten]

I thought the thrust of the programme was that we don't actually know, but best estimates suggest if we all lived as frugally as sub saharan africans we could sustain 15 billion, but if all we lived with the profligacy of the west then 3 billion might be too many.

Ultimately it is a question of resources - energy, water & agricultural land.

Exactly. You need to include the amount of energy and resources that is used by the population in question.

I read somewhere that based on solar power alone (assuming they mean non-fossil and non-nuclear) our planet allowed about 1 billion humans to live before we found ways to take advantage of fossil fuels and nuclear power at much larger scales.

[litespeed]

Kieth - You asked: "How long until our population becomes unsustainable." No one knows because important variables are unknowable. The first variable, of course, is food production/distribution per individual.

This variable has developed very much to the benefit of human population over the last century. Specifically,  food production shortages have been a plaque on human kind for almost the entirety of recorded history. Yet, ironically, the earth now is agriculturally able to support orders of magnitude more humans then it did 2,000 years ago. When was the last Chinese famine, for instance.

Now separate this combined variable into two parts. First, food production; second, total population. Excess food production is huge. Large quantities of food stuffs are actually used for other purposes. For instance, corn (maize) is used both to produce automotive fuel and animal protein. The same is true for palm oil.

Second, population trends are good and getting better. The estimates vary, but depend on whether the nations involved have become industrializes or not. The industrial world, including China, have fertility rates that are at or below replacement levels. Absolute increases will continued until deaths match births, but the population is unlikely to double by the year 2100 IMHO.

So, in general, while populations continue to increase, the trend is quite good. In addition, excess food production is currently huge, and certainly can be shifted from non-food uses to food consumption if things get bad enough.

Then there is the weather. We have been in something of a climate optimum for food production for almost the entirety of the industrial revolution. There is no guarantee this will continue. Happily, we may be in a cooling snap that could test the limits of food production, especially in the continental climates such as North America.

For instance, Canada is a major world grain producer. If its growing season is substantially reduced by climate cooling that would be a BIG leading indicator. Unhappily, sunspots seem to be an inversely proportional leading indicator. Sunspot cycle 24 has been missing for years, and may soon be presumed dead.

In addition, the entire Northern Hemisphere seems to have presented itself this year specifically for testing my adage: Warm is good, cold is bad. Accordingly, agricultural production in the next couple of years is worthy of very close observation.

Total world population carrying capacity? Depends on total world food production. The 'Green Revolution' may have peaked already. I specifically point to Africa, much of which refused American Genetically Modified grain for food, let alone to plant. Never mind just about the entirety of the American population eats the stuff or uses it for fuel or to provide really really nice Porter House steak.

In the long run, world population will eventually stabilize. Either by fertility reduction, of famine. At that time we will know EXACTLY what is total planetary carrying capacity.

[yor_on]

Don't worry, there will be a war before that