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Comment by topmonk | Hacker News Reader

As a thought experiment, we release 40 billion tons of co2 per year. An average skyscraper weights around 250,000 tons. So that would be the equivalent of 160,000 skyscrapers worth of this stuff. Hong Kong has the most skyscrapers current at 317. So it would be the equivalent of building the skyscrapers for a city that is 500 x the size of Hong Kong every year.

Not that you'd have to build skyscrapers with the material, but just to put this idea in some sort of perspective.

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Skyscrapers are mostly empty space inside. The Great Pyramid of Giza weighs about 6 million tons, so we’d be producing about 7000 of them annually. Maybe we could just plop them all in the ocean? ;)

I'd probably mess up the arithmetic, but I wonder how many skyscrapers or Great Pyramids could be packed in a volume of 1 cubic mile. That's how much oil we use per year.[0] (All sources combined are equivalent to about 3 cubic miles of oil.)

It would be nice to find a way to bump that up a couple orders of magnitude without actually pulling that much oil/equivalent out of the ground, since there literally isn't enough there.

[0] https://en.wikipedia.org/wiki/Cubic_mile_of_oil

Start with a Great Pyramid of Giza, or locally sourced substitute following the traditional recipe [1]:

  * 5.5 million tonnes of limestone
  * 8,000 tonnes of granite
  * 500,000 tonnes of mortar

For a simple approximation, we ignore ingredients that are not limestone.

mass of limestone in great pyramid of giza

  = 5.5 * 1e8 kg of limestone

Volume of limestone in one great pyramid of giza, assuming medium-high density limestone at 2500 kg / m^3 [2]

  = 5.5 * 1e8 kg / (2500 kg / m^3)
  = 2.2 * 1e5 m^3

allegedly there are 4.168e+9 m^3 cubic metres per cubic mile. That gives about 19,000 great pyramids of giza per cubic mile.

[1] https://en.wikipedia.org/wiki/Great_Pyramid_of_Giza#Material... [2] http://www.natural-stone.com/limestone.html

edit: when i try to estimate by geometry from the pyramid dimensions, instead of by density, i end up with about 2,000 great pyramids of giza, but that's without trying to understand what the volume of a pyramid actually is, because i am not clever enough to do that.

Intuitively, isn't the volume of a pyramid going to be 1/3 of that of a prism with the same width/length/height?

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