There isn't much of what you'd call a conventional setting in this poem, unless you consider the vague concept of "Apocalypse" (or the end of the world) to be a setting. But every poem has a setting of some kind, because language has a funny way of popping images into our heads.
"Fire and Ice" begins with two images of the end of the world. In the first, the world is a great bubbling mess of fire, lava, and explosions. Cities are melting and trees are burning. In the second vision, the world is an ice-cube…er…ice-sphere. A great cloud looms above the earth, and temperatures are so low that life cannot survive.
From there we move to a discussion of how the speaker's experiences have informed his opinion. We have the image of him "tasting" desire, like Eve biting into the fateful apple in the Garden of Eden. Then he rewinds the end of the world somehow, as if this were a film. In the second Apocalypse, things run different. Ice carries the day, driven by the hatred of people like the twisted souls in the icy depths of Dante's Inferno (see "In a Nutshell" for more on this).