In Frost's "Fire and Ice" the world may possibly meet its end in two distinct ways. The first may be with fire; humankind's fiery passions, based on beliefs and ideologies, may be the cause of conflict that brings the world to an end. The world may end, not because of indifference, but to the contrary, because of strong feelings about long-held beliefs that different individuals or groups of individuals seek to defend. Fiery, narrow-minded passion, without reasoned discourse, may be the downfall of the human race.
The second distinct way the world may end is with ice. Frost alludes to ice being akin to hate. It is cold-hearted thinking that is selfish and doesn't take into account the Golden Rule - treating others as you would like to be treated.
Frost reveals that he has encountered, dealt with, and maybe even exhibited hate in his life:
"I think I know enough of hate"
Ice cold hatred is love for others 'waxing cold'. It is the opposite of fiery passion but produces the same destructive result for humankind.