Approximate the global use of fossil fuels as entirely coal combustion which can be approximated as pure carbon (sg = 0.8). Calculate the size of a cube of material are we taking annually from the ground and putting into the atmosphere (dimension of perfect cube in km)? Alternately, what surface area (km2) would it occupy if instead it was a mine that went 10m deep (10m depth seam of coal strip mined)? Use reasonable assumptions.