There’s 148.94 million km^2 of Earth land area, not ~500 million as you claim (which is about the entire surface area of the earth).
This is important because in the kinetic destruction section, you found that your lower bound on human habitation area is 5x larger than the total possible kinetic destruction area. However, your area number is 3.3x too big, since only 30% of the area is land area. Thus your lower bound is only 1.5x larger than the possible destruction area, which makes the bound weaker—it’s pretty plausible that nukes might get 1.5x more destructive or that the destruction would take out enough of humanity to be irrecoverable, and anyways is important if you care about the scale of nonextinction risks.
(I caught this error by knowing that the circumference of the Earth is about 40k km, from which you can quickly estimate the surface area).
There’s 148.94 million km^2 of Earth land area, not ~500 million as you claim (which is about the entire surface area of the earth).
This is important because in the kinetic destruction section, you found that your lower bound on human habitation area is 5x larger than the total possible kinetic destruction area. However, your area number is 3.3x too big, since only 30% of the area is land area. Thus your lower bound is only 1.5x larger than the possible destruction area, which makes the bound weaker—it’s pretty plausible that nukes might get 1.5x more destructive or that the destruction would take out enough of humanity to be irrecoverable, and anyways is important if you care about the scale of nonextinction risks.
(I caught this error by knowing that the circumference of the Earth is about 40k km, from which you can quickly estimate the surface area).