I think the biggest problem facing humanity and life on this planet is the desertification of the land.

Designing human habitats utilizing permaculture principles aim to create sustainable living and surplus which is returned to the earth which in turn grows a healthier planet.

An example would be Geoff Lawton. He is someone who has had several projects, including I believe in Jordan and Israel, which are a proof-of-stake that this works in even the harshest of conditions.