How many people will need to be given piggybacks in 472 years?

June 12, 2008 1:33 PM

Help with a large, stupidly theoretical question involving sea rise, population growth, and human development... should be fun.

Here are my initial estimates:

Population growth is 1.167% a year.
Earth's land area is 148,939,100,000 square meters
At one square foot for the average human footprint (both feet), this makes a 0.0929 square meter footprint.

If you don't change the population growth (food limits, disease, technological changes, wars etc), and starting with 6.7 billion people today, I work out that in about 472 years the entire land area of the Earth will be covered by human feet.

I didn't factor in an equation for the increase in the percentage of population growth over time, and I estimated the size of the human footprint, so any revision of this would be appreciated.

Current sea level rise is (roughly, considering the differences in opinion) around 2 millimeters a year. Without factoring in the change of sea level rise (the predictions are so varied), I work out that in 472 years the rise in sea level will be 0.944 meters.

So what percentage of the earth's land lies below 1m elevation? I'm trying to work out what percentage of people will have to be giving other people piggybacks in 472 years.

If anyone wants to factor in best/worst estimates, or anything else, everything will be welcome.

Sorry for the long question, and Thanks!

posted by omnigut to science & nature (18 comments total)

Other things to consider;

If Moore's law about transistors continues without changing (number of transistors in the average computer doubling every two years), in 472 years what will the specs be of the average computer?

If current increases in the speed of planes (decade by decade) continues, how fast will we be able to travel in 472 years (forgetting fuel price or speed of light)

If decade by decade fuel prices increase as they are, how much will a gallon of gas cost in 472 years?

If anyone else can think of good questions/answers for this 472 year thing, feel free to add them yourself.
posted by omnigut at 1:58 PM on June 12

Also, with so many people standing on land, they'll be pushing it further into the sea, like a swim platform overloaded with kids... thus causing the oceans to rise even further!!

I jest.. but who knows if the population will always grow? Who knows if it will stagnate or skyrocket in 200 years (if we're even still here). Population growth is definitely not exponential, as many (Malthus) have historically posited. Also, as you've pointed out, this is so stupidly theoretical that any "logical" assumptions you make will probably not help you to get any closer to a real answer than some random, wild, illogical assumptions.

Good luck!
posted by mbatch at 2:01 PM on June 12

I don't think it's correct to assume an upward, constant curve. Are you accounting for tsunamis, nuclear war, or dogmatic governments that prevent multiple births? Your scenarios don't account for diminishing returns or diseconomies of scale or hypothetical chatfilter.
posted by mattbucher at 2:03 PM on June 12

Yeah, this is why the question is stupidly theoretical, but I'm trying to work it out for the benefit of a poem written about a guy on a spaceship on the way to Alpha Centauri, who left because he didn't want to give a piggyback. It also factors in the incredible amount of empty space in the universe, the incredible amount of empty space in an atom, and tries tying together just how insignificant people really are, how weird out view of ourselves is. You know, fun, lighthearted things like that. :)
posted by omnigut at 2:11 PM on June 12

You are not factoring in human ingenuity with regard to land reclamation.

It's OK. Most of the "oh noes the sea levels are rising we're gonna drown" types forget about that. I partially blame the CGI shots of Manhattan underwater in An Inconvient Truth.

Land amounts added

* Netherlands - about 1/5 land from land reclamation or about 7.000km².
* South Korea - As of 2006, 38 percent or 1,550km² of coastal wetlands reclaimed.
* Singapore - 20% of the original size or 135 km² as of 2003, plans for 99 km² more.[4]
* Hong Kong - Praya Reclamation Scheme began in the late 1860s that consisted of two stage totaling 50 to 60+ acres.[1][5] This figure understates the importance of the sites reclaimed: Hong Kong Disneyland, Hong Kong International Airport, and its predecessor, Kai Tak Airport, were all built on reclaimed land. In addition, much reclamation has taken place in prime locations on the waterfront on both sides of Victoria Harbour. This has raised environmental issues of the protection of the harbour which was once the source of prosperity of Hong Kong, traffic congestion in the Central district,[6] as well as the collusion of the Hong Kong Government with the real estate developers in the territory.[7][8]

In addition, as city expands, new town in different decade mostly built on reclaimed land, such as Tuen Mun, Tai Po, Shatin-Ma On Shan, West Kowloon, Kwun Tong and Tseung Kwan O.

* Macau - 170% of the original size or 17 km² [1]
* Tokyo Bay, Japan - 249 km².[9]
* Kobe, Japan - 23 km² (1995).
posted by Cool Papa Bell at 2:13 PM on June 12

Assuming that your facts on earth's land area, and area for human footprint are correct...you would need 1.6 TRILLION people. This seems like an impossibility to me (in 2008), although I'm sure a lot of people would have thought reaching 1.6 Billion would have been an impossibility in 1491.

If you want me to throw a wrench in your problem, I can do so. Lets assume that human pop. growth IS constant for 472 years. It will grow by about 1.5+ trillion. To get that many humans, we need to extract water from our biosphere (we only have a limited amount, right? None is coming from space). We would need MORE 7.37592051 x 10 ^13 liters of water in human bodies (calculated by:
difference in population then and now times 2/3[avg % of human body that is water]times 70 [avg volume of water in human body])

Take that much water out of the ocean since its the big eventuality that is affected by fluctuations of water. Sea level will drop a little too...

and thats just ONE SMALL thing.

Good luck, I am kinda excited to read the calculations that other people wrote.
posted by hal_c_on at 2:17 PM on June 12

Just looked at the Chat Filter FAQ. I hope that the fact this question is in aid of my next book of poetry will excuse it. Perhaps it doesn't, and I apologize to the Metafilter Community for that.

Sorry Mattbucher, too, and thank you for the links.
posted by omnigut at 2:18 PM on June 12

This question is teetering dangerously close to the ultimate question, which I've always been a little disappointed we never got to discuss further.
posted by allkindsoftime at 2:21 PM on June 12

In this article about elevators, Paumgarten gives a larger estimate for how much space each person takes up:

Fruin introduced the concept of the “body ellipse,” a bird’s-eye graphic representation of an individual’s personal space. It’s essentially a shoulder-width oval with a head in the middle. He employed a standard set of near-maximum human dimensions: twenty-four inches wide (at the shoulders) and eighteen inches deep. If you draw a tight oval around this figure, with a little bit of slack to account for body sway, clothing, and squeamishness, you get an area of 2.3 square feet, the body space that was used to determine the capacity of New York City subway cars and U.S. Army vehicles.

So if this is right (which I think it is, if we don't account for 472 years of progress in obesity, for example), then you will fill up your available space more than twice as fast as you are estimating.
posted by Forktine at 2:25 PM on June 12 [1 favorite]

The transistor point may be moot because of future advances in things like biological computers and multigate transistors obsolescing the "standard" FETs and BJTs. In 472 years we might have the equivalent of a slave virus that reads and plays back MP3 files encoded on other virus' (virii?) backs, and is fed by some magical space-age protein battery. (I wonder how the animal rights people will figure into all this?) Anyway, my point is that numbers won't help you predict things like that because of random innovation. Someone will finally invent the safe nuclear car or the practical solar car and we'll get away from this petroleum addiction.

On fuel prices, if you account for inflation, they haven't risen all that much in the last 90 years.

As far as population growth...I defer to the movies. Remember Demolition Man? Some plague will confound the statisticians. After AIDS there was NRS and after NRS there was UBT! Or there will be...asteroid trouble. Fractal monsters from outer space? The Second Coming? Who knows. It won't be what your graph shows, though.
posted by ostranenie at 2:25 PM on June 12

Okay, so can I get an answer to this very important point: How much of Earth's land area lies below 1 meter above sea level? If that makes sense...
posted by omnigut at 2:32 PM on June 12

14,000 sq miles in the US would be affected by a 1 meter sea level rise, though half of this is already wetland (source)
The US land area is 9,161,923 sq km (source)

Therefore about 0.4% of the US's land area would be affected.

Assume the global percentage is probably on the same order, maybe between 0.1% and 1%. Sound reasonable?
posted by PercussivePaul at 3:10 PM on June 12

You are not factoring in human ingenuity with regard to land reclamation.

It's OK. Most of the "oh noes the sea levels are rising we're gonna drown" types forget about that.

Engineering-intensive reclamation techniques with limited reach and results that are probably linear at best are a possible counter against limited sea level rises.

Against a theoretical exponentially increasing population, they're pretty forgettable.

The fortune/misfortune that's likely going to keep that from being a problem is the limits on exponential growth.
posted by weston at 3:21 PM on June 12

As another bit of sci-fi context, I've always liked to believe that the planet in the Star Trek episode The Mark of Gideon was entirely dense with bodies.
posted by rlk at 3:23 PM on June 12

Map of earth with adjustable sea level

(answer: a 1m sea level rise would not change much in terms of land area, though as cities tend to be built on coasts it'd have a disproportionate effect on society. If it happened gradually over 472 years we'd probably be able to cope just fine.)
posted by ook at 3:35 PM on June 12

On the price of gas issue (though this applies to other aspects of your question), you can't take the price movement now and apply it as a constant to the next ~500 years. If you look back at oil prices, there was never a period with anything close to that long of steady prices or steady rises. Things that vary greatly over years and decades (like oil prices) are infinitely tough to predict over centuries. Things that vary over centuries and millenia (global warming, sea level rise) make for somewhat more plausible predictions.

Oh, and it's hard to imagine a world in 472 years in which we're still using oil. Long before then the prices would have been so high as to make an alternative an economic certainty.
posted by twirlypen at 4:40 PM on June 12

You know, the population growth rate is not stable and has been declining since the 60's.
posted by nanojath at 7:55 PM on June 12

Thanks everyone. I've done the poem now, and couldn't have done it without you
posted by omnigut at 11:07 PM on June 12