Suppose that one of the 4 elements (earth, water, fire, air) will cease to exist in 20 years.
What will happen to the world? And what will happen to humankind?
Earth disapears; The earth earth beneath us will literally disapear and we die.
Water disappears; Humans are about 70% water, so we die. Even excluding that, we don't drink for 3 days, we die.
Fire disappears; it would take a max of 18 minutes(probably) to freeze to death.
Air disappears; We suffocate and die.
We would die any which way.