How does the environment enhance the story?'The Sun Also Rises'
The environment or setting of the story, to be comprehensive, includes both time and place. The first reference below explains the historical background of the novel which complements so well its main themes:
For members of the upper middle class or the rich, the twenties were indeed the era of prosperity, debauchery, and bootlegging. For the rest of humanity, life was still a struggle. The 1921 musical “Ain’t We Got Fun” encapsulates the period saying, “The rich get richer, and the poor get children.”....The picture for blacks in America was especially hard with 85% of blacks living in the segregated south and 23% of them illiterate. Great numbers of blacks began migrating north to the cities with lasting demographic effects.
The bullfighting scenes throughout the story imply both internal and external conflicts and are highly charged with sexual connotation, particularly in terms of Jake's emasculation. Have a look at the second reference (on themes) for more insight into this aspect of the novel.
This question is good. It's not something that I usually think about when I read Hemingway, but environment really is important in most or all of his novels.
The action of The Sun Also Rises takes place mostly, as I recall, in the densely urban setting of Paris, France. This city is certainly interesting to and enjoyed by the main character, Jake Barnes, but it also has its flaws. Jake's encounter with the "poule," which may mean something close to "prostitute" -- I think her name is Georgette -- emphasizes the sickness of modern, urban life. (A similar compounding of the ideas of sickness, sexual activity, and urban settings can be seen in other pieces by Hemingway, including "A Very Short Story.")
There are several other environments in the novel, however, including the natural setting of the fishing trip and the less developed village where the fiesta is held, both in Spain. If there is joy and peace in the novel, it's more likely to be found in these two places, not in Paris.