I do actually have receipts. For example numbers I picked Washington DC, which has 700k people that each use an average of 600 kWh per month. That's 5 TWh / y

I do actually have receipts. For example numbers I picked Washington DC, which has 700k people that each use an average of 600 kWh per month. That's 5 TWh / year, which I rounded up to 10 TWh. This yields 475 m^3 of helium, which is 85 kg. I rounded up to 100. DC is a modest city and all of humanity uses 15000 TWh / year (of heat). This "100 kg / city / year" estimate is even on the lower end since I started with electric consumption and never put in the factor of 3 to convert to thermal. Your mass-energy conversion number is within error of mine, but your estimate of how much power we use is much lower. https://www.wolframalpha.com/input?i=%2810+TWh%29+%2F+%2817.59+MeV%29+%2F+%28avogadro%27s+number+1%2Fmol%29+*+%284.002602+g%2Fmol%29+%2F+%280.1786+g+%2F+liter%29 https://www.wolframalpha.com/input?i=%2810+TWh%29+%2F+%2817....