Why do you have to save the world?

Humanity can't survive by itself. To live in the Earth, the men need food, shelter, and raw materials. Obviously, nothing of that comes from emptiness. The man must live harmoniously with nature. The humanity needs water, air, plants, animals, etc.; everything is important to the life maintenance in Earth, since the smallest virus to the biggest ocean.

People living harmoniously with nature in a Chinese village.
So, it’s more than important that the men change your relationships with the natural recourses. The sustainability isn’t just an Esthetical question or a way to “pay” to the nature all the human costs. The humanity needs to save the world to save itself. It’s an obligation, a must, a situation the humankind can’t forgive.
The next time you’re in a supermarket and don’t buy a biodegradable detergent because it’s too expensive, you must remember that the life in the Earth costs more than $1.99, and maybe your son or daughter won’t swim in the river or drink fresh water, because the last river will be empty of soul and life.