It’s based on some estimate of sustainable consumption, i.e. the earth can sustainably support everyone if their average footprint is “1 earth.” Any higher leve

It’s based on some estimate of sustainable consumption, i.e. the earth can sustainably support everyone if their average footprint is “1 earth.” Any higher level of consumption is unsustainable. I’ve seen multiple variations on this concept, so you’d likely have to consult their specific methodologies to figure out how they determine what is sustainable.