Ten in 2010, ten in 2010!

February 26, 2006 1:59 PM

How much life can our planet sustain?

Or, rather, how much human life?

My girlfriend asked me this today, and I've no idea where to even begin a back of the envelope calculation. Assuming that 25% of the people on earth live in 1st world countries, and the rest consume resources as third worlders... how many human lives can our planet support?

I'm pretty sure agriculture would be the limiting factor, given that the population density of the livable portion of the earth's surface is pretty low. I don't think we're going to run out of room any time soon. Am I right in thinking food is what will run out first? How much can we make?

P.S. No, we are not high.

posted by jammer to science & nature (26 comments total)

This is really impossible to answer as we keep discovering technology that increases the production possibility curve, making more of the so-called finite resources. Through advanced technology we would presumably be able to support a totally Manhattanized world. It's technically, but not economically feasible to mine asteroids -- one of which would hold more iron ore than all of the iron on Earth.

Keep in mind also that in our current economic structure it becomes quite expensive to maintain current income levels and raise a lot of children, a self-limiting way of keeping population levels in check.

So there's really no way to tell how many people our world could sustain unless we wish to throw out time (i.e. economic development) and keep everything in state. Even if you were to, say merely find out how many resources a person in the first world consumes as of date and multiply it out you'd be dealing with a lot of shaky numbers (available energy reserves are really unknown, and all raw materials estimates would fluxuate depending on where you get your information from).
posted by geoff. at 2:08 PM on February 26, 2006

The question is not "how many", but "for how long".
posted by meehawl at 2:14 PM on February 26, 2006

I think the term you are looking for is the carrying capacity of the Earth. The dieoff site meehawl suggested, has a page on this, and Joel Cohen wrote a book on it. The exact number seems subject to debate by people better qualified than me to answer this question, so you'll have to read up on it some more and draw your own conclusions.
posted by Fat Guy at 2:26 PM on February 26, 2006

Well, given some cursory googling, it looks like you can get about 200 pounds/acre of rice per harvest. According to the bag of rice in my cupboard, 45g of dry rice has about 150 food calories, so that 200 pounds should contain 302,250 food calories, or enough to feed someone on a 1656/day calorie diet for six months. Let's be more generous and give people a 2484 kcal/day diet. (1 food calorie = 1,000 metric calories). In that case, one person needs to product of 3 acres of arable land in order to survive. According to wikipedia, there are about 12 million square miles of arable land in the world, or seven billion acres, or about enough for 2.5 billion people.

Now, at this point I'm thinking the 200 pounds/year figure is a bit low, but you should be able to use the same math With any figure just knowing the pounds/per acre yield and the calories per unit of weight. In comparison.

Intrestingly, according to this page 500 calories of energy are burned in the process of putting one calorie of energy in food on the table.
posted by delmoi at 2:29 PM on February 26, 2006

Okay, wow I was way wrong on the pounds/acre figure for rice. According to that page Rice production in Missouri in the US was about 6800 pounds/acre. That's enough to feed 119 billion people 2500 calories/day if we could use all 12 million acres of arable land at the same capacity.

My guess is that we could probably squeeze in another 100 billion people by converting more land, bio engineering higher yield crops and further restricting people's calorie intake.
posted by delmoi at 2:33 PM on February 26, 2006

Depends on how big the lifeforms are. The total biomass of unicellular organisms is probably a large multiple of that of insects, which themselves add up to a large multiple of mammals, etc.

Basically, the answer to your question is some function of the question "how much energy (usable by photosynthesizing organisms) does the sun send to earth?" If you want to throw human ingenuity in there, we're splitting the atom and that's nice, but that's still a vanishingly minute percentage of the amount of energy that earth's plants extract from sunlight every single day.
posted by evariste at 2:48 PM on February 26, 2006

evarist is zeroing in on the concept of trophic level. Humans are heterotrophs, existing at the top of the food chain, a quite inefficient mechanism for kicking the energy derived from sunlight from plants and other photosynthesisers up a few ecological levels.

One way to support more humans per square metre is to start eating further down the trophic levels, avoiding some of the x100 and x1000 energy losses that occur. This is already happening with ocean derived calories. We long since ate up most of the top predators in the ocean and are now methodically scavenging our way down the food chain. Eventually we could all be eating jellyfish and plankton.
posted by meehawl at 3:05 PM on February 26, 2006

It's arguable that the Earth cannot sustain the current population since an enormous area of the globe is affected by undernourishment. Most of it is likely characteristic of social issues (wars, economic instability, etc.) but if you check out a similar map detailing the population growth it's hard to ignore the fact that it is largely the same areas affected.

As geoff mentioned, in the last 50 years the Green revolution has drastically altered crop yields that has allowed our current population (which has grown exponentially in the last 40-50 years) to enjoy the current abundance of food (particularly in richer nations). However, the techniques involved in the higher yield crops come with a cost. Only certain types of crops are amenable to the type of farming involved and that has significantly reduced the variation in certain arable regions and it is affecting the soil to such a degree that we are losing valuable arable land in areas that have been feeding us for decades (See: Biodiversity). Also, the technology involved is getting ever more complex that it requires more energy every year in order to grow the same amount of food (not accounting for new technology which could make this argument obsolete).

An ever more pressing concern for sustainability is the environment. Massive environmental shifts could have drastic effects not only on global food production, but migration out of areas previously habitable but rendered inhospitable by fluctuating ocean temperatures, earthquakes, or hurricanes could set off social and economical imbalances that will almost definitely lead to war. Nothing good can come out of a world filled with desperate people and nuclear armaments.
posted by purephase at 3:08 PM on February 26, 2006

Taking the amount of productive land and the statement that there's twice as much land used for pasture as there is cropland from here, and the estimate of 0.27 hectares of cropland per person here, one could guess that with the current yields and land utilization, if you took every single bit of land on earth to make food for humans, you could feed 8.5 billion or so. On the plus side, you could improve yields and efficiency in various ways. On the minus side, the amount of productive land is declining, and various other relevant natural resources (water and energy) are probably too scarce to do it that way.

I imagine it would be pretty easy to come up with reasonable-seeming estimates anywhere between 2 billion and 20 billion.

According to that page Rice production in Missouri in the US was about 6800 pounds/acre. That's enough to feed 119 billion people 2500 calories/day if we could use all 12 million acres of arable land at the same capacity.

That's pretty cool. If everyone ate lots of rice, we could feed a lot of people. I can't see anything wrong with those numbers. Except that I guess only a relatively small fraction of those 12 million acres are actually suitable for growing rice in that way. And of course people can't live on rice alone. And it takes a lot of water, energy, and nitrogen fertilizer to farm rice that way.
posted by sfenders at 3:21 PM on February 26, 2006

Thank you purephase, flagged as fantastic.
posted by baphomet at 3:26 PM on February 26, 2006

The Oil We Eat.
posted by meehawl at 4:17 PM on February 26, 2006

In my public health classes, this topic was discussed extensively over the course of an hour-long lecture by Allan Rosenfield, dean of the Columbia school of public health and an expert on the subject of global population health.

He noted arguments that the current figure (6 billion) might be over carrying capacity, talked a bit about delmoi-style back of the envelope calculations and their shortcomings (man cannot live on rice alone; not enough fresh water to farm all the arable land; energy production to desalinize that much water would cause global warming from waste heat yadda yadda yadda), and finally endorsed a figure of 17 billion humans, living a lifestyle very different from the modern American one.
posted by ikkyu2 at 4:32 PM on February 26, 2006

According to this (which appears to be a somewhat serious attempt to look at the problem), the minumum amount of land you need to feed one person is 0.07 hectares. As of 1990, they say there were 0.27 hectares of arable pand per capita. That works out rather close to the 17 billion maximum quoted by ikkyu2. But there may be problems with water availability, pollution, and soil degredation. And we will run out of fossil fuels eventually, which might make things sort of difficult.

the world may learn the limits of sustainable food production and their relation to population growth only in retrospect, because we are far from fully understanding them today. The ongoing loss of per capita arable land indicates how much human ingenuity and labor will have to accomplish—continuously and sustainably—to keep food production ahead of food demand.
posted by sfenders at 4:48 PM on February 26, 2006

I read a paper related to this about ten years ago, but I can't for the life of me remember the title or the name of the author. However, I do remember it had to do with the balance of plants and sapient life on the planet, and had a fairly long analysis of some computer simulations involving black and white daisies.

For some reason I keep associating it with Ada Lovelace, though I'm 99% certain that it's an erroneous correction - partly because the paper was based on theories which were (at the time) about ten years old. (That and her field was mathematics and not ecological physics.)

Can anyone shed some light on that? I have a feeling it could be of interest with regard to this question.
posted by Incharitable Dog at 4:53 PM on February 26, 2006

ISTM that we won't have real sustainability until we replace the resource->producer->consumer->waste model with something more cyclic.

At present, we rely on an assortment of random ecological processes to close that loop (i.e. perform the waste->resource step). In many cases (e.g. toxic chemical waste, nuclear waste, waste heat) we are already making waste at a higher rate than the rest of the ecology can reprocess. Therefore, we are presently above carrying capacity.

According to my own back-of-the-toilet-paper calculations (combination of gut feel and figures pulled out of my arse) the sustainable human population is about half what we currently have - somewhere in the three billion region. More than that puts too much stress on the rest of the ecosystem, and as it degrades, so does our quality of life.

It might even become politically feasible to arrange our affairs so that three billion of us could all enjoy first-world levels of resource security; but this will not happen if we maintain our present rate of resource->waste conversion.

On preview: Incharitable Dog, you're talking about James Lovelock's Gaia hypothesis.
posted by flabdablet at 4:57 PM on February 26, 2006

Jammer, you might also be interested in reading some stuff from the Rocky Mountain Institute.
posted by flabdablet at 5:13 PM on February 26, 2006

Your answer, inscribed in stone.
posted by hortense at 5:19 PM on February 26, 2006

You might want to consider what happens if you take all those "unused" acres and press them into agricultural service. It's been done before, we have examples:

Easter Island (Rapa Nui) is a good example of a society that overexploited the resources of their world. The end result was that they permanently lowered the carrying capacity of their environment, something that in turn destroyed all of their societies.

China has a looong history of intensive agriculture. They also have a very high productivity per acre, among the highest in the world. Essentially every possible, or sort-of-possible, acre that can be farmed is being farmed. What they have found is that this is a bad idea, you get side effects like desertification and uncontrollable flooding, and you tend to run out of trees. This is the basic factor driving their one child per family policy. They realised that total agricultural production just wasn't working for them, even though they are world class good at it.

Haiti is an excellent example of a country that is overusing and stripping its bioshere right down to mud. You can expect to read about various "natural" disasters there in the future, mudslides and famines and what have you. The odd thing is that these events are presented in the news as being unexpected surprises rather than predictable consequences of their actions.

In North America, currently a major food exporter, we have large areas where we are steadily strip mining the soil and water. If other factors remain steady, North American food production will drop when as they run out.

Arable land is important, but it is only one consideration. What level do you want all these billions to live at? Will meat be a regular part of their diets? Will they all live on soybeans and river water? Will these people also have electricity, heat, the use of wood and plastic and metals?
posted by Ken McE at 6:02 PM on February 26, 2006

Jared Diamond talks about this in Collapse, too. He points out that 1 person living a first world lifestyle takes up the resources of many (20 or so?) people living a third world lifestyle. So, we always think of running out of resources in terms of adding more people to the planet... but we should also think about the fact that, as more and more people attain first world living standards, they consume more. Estimates on how many people the world can support vary wildly - some say we're not supporting the people we currently have, others say we could support 2 or 3 times as many as we've got. But nobody thinks we could support the equivalent of 12 times our current resource usage, which is what we'd have to do if everyone living today suddenly attained first world living conditions.
posted by selfmedicating at 6:25 PM on February 26, 2006

but we should also think about the fact that, as more and more people attain first world living standards, they consume more

First, I'd like to point out that "1st world" and "3rd world" became meaningless when the "2nd world" disappeared about 15 years ago. What you're talking about are developed countries and developing countries.

Second, developed countries don't have population growth, aside from immigration, so it's only in an entirely hypothetical universe that we sustain the population growth rates of developing countries while adopting the consumption rates of developed countries. In reality, we face one problem or the other , but not both.

Third, it doesn't matter how much food there is in the world if we lack the means to distribute food around the world. There is currently no shortage of food, but people continue to start to death because we can't (or won't) efficiently transport food from areas of abundance to areas of need. So how much life our planet can sustain depends largely on where the people are living. Unfortunately the areas with the fastest growing populations tend to be those that can least sustain them.
posted by scottreynen at 6:49 PM on February 26, 2006

17 billion is nuthin', if you really wanted to maximize human population.

The key to this misguided adventure would be to abandon agriculture in favor of industrial production of food. Carbon, hydrogen, oxygen, nitrogen, and trace elements go in one end of the food factory, energy goes in, and food comes out the other. It wouldn't need to be appetizing food, just able to sustain the body.

If you can get this working, you can kiss off the rest of the biosphere and use it as feedstock for the food factories. Seawater has oxygen, hydrogen, and at least some trace elements, carbon is easily available in dead life forms and coal or other rocks, and there's enough nitrogen in the atmosphere to last for a while. As for energy, if you're really determined you ought to be able to drill down deep enough for large-scale geothermal power.

The existing mass of people would primarily eat sewage that was broken and and resynthesized into food. New resources could go preferentially towards increasing population, as could reprocessed corpses. All human effort could be devoted to building new residences and maintaining them, building new food factories and maintaining them, and extracting new sources of carbon and trace elements.

It wouldn't matter how much arable land there was, and all land could be taken up with arcologies (sealed up if you've fubared the atmosphere, as you probably have), as could much of the sea surface. I bet you could hit 50--100 billion easy, and your eventual problem will be disposing of the waste heat from the food factories and the generators supplying them.

ObSF: the Puppeteer rosette, but they still have agriculture on their other planets.
posted by ROU_Xenophobe at 7:03 PM on February 26, 2006

scottreynen, you're wrong on all counts. "Developing" is going out of style just like "3rd world" did. The cool kids are calling them "emerging" markets/economies/nations now.

We do have both problems in the same places: increasing resource consumption and population. While it's true that there seems to be a level of development where population growth slows down (though not always to zero), there is a lot of "developing" to do before India gets there. The population when (if) they do get there will be larger than it is now. Not that population growth and increased consumption are both necessary to cause problems; either one would do.

And it does matter how much food there is in the world if, no matter how we distribute it, there isn't enough to go around. While it may still be true that there is more than enough to feed everyone if it could somehow be distributed equitably, it won't be true for long.

ROU_Xenophobe: As for energy, if you're really determined you ought to be able to drill down deep enough for large-scale geothermal power.

Surely it would be easier to build a space elevator and use orbital solar power. Although that would I suppose go beyond the scope of the question, since it wouldn't strictly be relying on the resources of "our planet".
posted by sfenders at 7:29 PM on February 26, 2006

I apparently didn't have any cool kids teaching my international studies courses. Nor are there many on Wikipedia (vs. uncool). Whatever replaces it, it's time to stop using "3rd World."

I didn't mean to suggest we won't have a lot of people overconsuming (we already do), just that we won't have a population that is both increasing too fast and consuming too much. Once we start overconsuming, we stop having so many kids.

India's population growth rate is relatively low for a developing country (compare to Chad or pretty much all of Africa). It's only an issue because it's growing at all, and India is already huge. India is still far from developed rates of consumption. The per capita energy consumption in India is about 480kWh. In America it's over 12,000kWh. (Chad is 11kWh.) So India is a slight overpopulation concern and a slight overconsumption concern. As one concern grows, the other will shrink. That's how it generally works anyway.

Food distribution is a current problem. Having enough food is a hypothetical problem. In a hypothetical world with both problems, either would make the other irrelevant, but I personally consider current problems before hypothetical problems.
posted by scottreynen at 8:51 PM on February 26, 2006

I think calling poor countries "developing" or "emerging" is pretty suspect.

Is there evidence that, over time, more and more people worldwide "attain first-world status," as selfmedicating says?

Calling them "developing" or "emerging" seems to me to assume a "progress" narrative of ever-improving conditions for everyone, as uneducated natives stop hunting and gathering and learn about farming, then stop farming and learn about computers and cellphones and make lots of money and everyone has clean water and things are great, and it's all about ingenuity and democracy and bootstraps and not about colonialism and exploitation and geopolitics.

I don't think that's really how things work, but I can understand why people would want to think that, and it seems to serve the same purpose as the myth of American class mobility.
posted by crabintheocean at 8:52 PM on February 26, 2006

ROUXenophobe: The 17 billion figure didn't assume invention of any major new technologies.
posted by ikkyu2 at 12:17 AM on February 27, 2006

It wouldn't matter how much arable land there was, and all land could be taken up with arcologies (sealed up if you've fubared the atmosphere, as you probably have), as could much of the sea surface. I bet you could hit 50--100 billion easy, and your eventual problem will be disposing of the waste heat from the food factories and the generators supplying them.

100? According to my calculations above, 100 billion people could be fed using today's agriculture, using the currently available arable land.
posted by delmoi at 1:01 AM on February 27, 2006