7 Gpeople

While at a conference in Istanbul, I went to the İSTANBUL ARKEOLOJİ MÜZELERİ, which was an absolutely fascinating archeology museum. Istanbul has featured prominently in the growth of civilization, and I struggled to keep track of the many different civilizations and cultures that occupied the region at one time or another. I had to find a youtube video to help me sort it out.

There was a very nice exhibit on Troia (Troy), which apparently really existed; it's ruins were unearthed in a farm field not too far from here. It was settled, destroyed, and resettled in 9 different epochs before being ultimately abandoned. Even back then, it seems that anything you dug up had a 1000-year history. Buildings were built on top of buildings. The reconstruction of the different settlements was interesting.

It was really hard for me to get my head around how small cities were in comparison to now. Istanbul currently has 13 Mpeople living in its greater metropolitan area. In 3000 BC, that was the human population of the world. The largest cities in antiquity were ~250 kpeople. It made me wonder if all of our advancements in technology and culture in the last couple hundred years could be attributed strictly to 1) more people to do the work and 2) longer tails on the normal distribution of people with various abilities.

So just how many people were there as a function of time? The log-log plot above from wikipedia shows current best estimates. Apparently, some 70 kyears ago, possibly as a result of a major volcano eruption, the human population was reduced to something on the order of 1000 to 10,000 "breeding pairs." Since then, the population rapidly recovered to several million, where it remained stable until agriculture was developed. This is all in a nice video tracing genetic migration via mDNA.


Since then, there has been exponential growth (a line on log-log plots) with a transition to a slower growth coefficient at ~400 BC. Occasional Black Plagues aside, the human population has increased dramatically. I remember hearing once that half the people who ever lived are alive right now. That's actually definitely false--it's closer to 6%. Also, everyone seems to think that population growth is accelerating (remember this video from the 80's ?). The graph above definitely shows that's not true, either.

But what is true is that this growth cannot continue unchecked without hitting its head on something, be it food supply, global warming, danger of pandemics, warfare, declining birth rates, or whathaveyou. It's estimated that in October of this year, 2011, there will be 7 Gpeople on the planet. This map shows where the population currently is, but it's estimated that much of the growth in the next century will happen in poverty-stricken Africa. Things pretty much have to plateau around 10 Gpeople, though.

So what to do? The most effective ways to reduce birth rates, which is key to controlling population growth, global warming, saving the environment, and many of the rest of our problems are:

1. contraception
2. improving the standard of living (ending poverty)
   
3. education (and education about contraception)
   
4. and reducing infant/child mortality

That last item is counter-intuitive. The reason it is important is that when survival rates are low, couples have more children to compensate, including a buffer for uncertainty. Having a predictable path from birth to adulthood allows for more precision in family planning.

Rain Water

I consider myself an environmentalist. I try to do the basic things around the house that help reduce my carbon footprint (you can calculate yours here) like installing compact florescent lights, installing power strips to prevent appliances like TVs from pulling current while "off", driving the minimum possible, eating vegetarian, and drinking soy milk instead of the dairy variety (cows are surprisingly bad for the environment). And I'm always on the look-out for something crazy and interesting to try for the environment. An idea I've been tossing around in my head (especially now that I live in rainy Puerto Rico) is harvesting power from rainwater. Part of my recent interest in rainwater, I must admit, has to do with the fact that we average about one water-outage per month here; I want backup water. However, my original interest, a year or two ago, was actually in generating electricity from the rain falling on my roof.

Here are some order-of-magnitude calculations for what I might expect to get from this. Quick research indicated that average annual rainfall here is 62 inches (about 150 cm). This means that each square meter of rooftop collects about:

150 (cm) x 100 (cm) x 100 (cm) x 1 (g/cm^3) / 1000 (g/kg) = 1500 kg

of water per year. If a story of a building is 5 m high, then the potential energy in that water is:

Force x Distance = Mass x Gravity x Distance = 1500 (kg) x 10 (m/s^2) x 5 (m) = 75,000 (J) = .02 (kWhr)

So PR generates .02 (kWhr/m^2/story) annually. My apartment building is about 10 (m) x 20 (m), and is 4 stories high, bring the energy of rainfall to 16 kWhr annually. If electricity costs $0.10 per kWhr, I could save a whopping $1.60 off my power bill annually. That probably won't ever offset what it would take to build the generator. Sigh.

Of course, dams do exactly the above, but with an enormous collecting area (not just a rooftop--an entire drainage basin). It looks like rain on my roof isn't going to power my computer, though. But I still might try to use the water to flush my toilet when the water goes off next weekend.