How Many Worlds do you Consume?

One of my daughters is writing a paper (and thankfully she LOVES to write) on the impact of humans on their environment.  So I showed her this extensive ecological footprint - Ecological Footprint - that she definitely needed me (she is only in sixth grade) to help go through. But then I found this easier one Footprint Calculator and amazingly it said roughly the same thing - that if everyone consumed the way we do, it would take 6.5 worlds to sustain us.  This might be a great exercise for your students to complete as it would bring up the question of how we live in just one world if so so many in your classes consume more than several worlds.