Wednesday, December 13, 2006

Weight of All People on the Earth

After reading that meat and dairy animals now account for about 20% of all terrestrial animal biomass, I became curious how they calculated that. Taking a look at the document, they attribute it to this report done back in 1979. Thanks to the wonders of the internet and cheap outsourcing to M S Swaminathan Research Foundation, in Chennai, India, we are all able to read that original report.

The calculation is done in this section on animal biomass which attributes to another article written in 1973. Man, I would have thought someone would have come up with a better estimate in the last 30 years, but whatever.

They figure the average weight of a human is 50kg (I wonder if that has changed since 1979?), so assuming there are 6.5 billion humans alive today that gets you to 325 billion kg.

Of course you are now wondering, how does that compare with the weight of all other animals on the planet? Glad you asked.

For some reason they like to compare in dry weight. A human is 70% water, so this gets you down to 97.5 bil kg. And they like to measure things in grams using scientific notation so that puts you at 97.5 x 10^12 g. They put total animal biomass at 2002 x 10^12 g dry weight and 1005 x 10^12 g for terrestrial ecosystems, so humans make up just about 5% of all animal biomass and 10% of all land animal biomass.

The UN report estimated that all livestock weigh .7 billion tonnes or 700 billion kg. This is a little over 2 times as much as humans (and makes you wonder who the dominant species on earth is). Assuming they have the same amount of water, that would put them at 20% of all land animal biomass and humans and livestock combined put as at 30% of all terrestrial biomass. That is pretty high, but nowhere near the 98% of all terrestrial vertebrates that Daniel C. Dennett wrote about.

The underlying assumptions on how the total biomass was calculated in this report is not clear, and things may have changed since 1973. I would really be interested to see an updated version of these numbers.

1 comment:

parabanger said...

It would be interesting to see the historical graph of total human mass as both population and percapita mass are increasing.

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