Chemist here (actually a biochemist/botanist)... anyway, you do not need that "^" in CO2, CO2 is just fine. Although what would be even better would be to have the 2 as a subscript, but I do not know how to do that in hubski yet.

My guess is that with this model the footprint estimates would be low since it seems these values are based on German figures, and Germany is very green. So, lets say I am sitting in an inefficient country that wastes resources... I have a feeling using my computer here might have a larger carbon footprint.