What are some similarities and differences in the setting and atmospheres of the two books, 1984 (written by George Orwell) and Fahrenheit 451...

In 1984 and Fahrenheit 451 authoritarian states practice mind control over their citizens. In Fahrenheit 451, the government has banned books and the central character, Montag, works as "fireman" burning books. In 1984, books are not entirely banned (Julia job involves churning our cheap romances), but the state works to control every aspect of its citizen's thoughts. Like Montag, Winston Smith works for the state's "mind control" apparatus. In his case, he alters newspapers to ensure that whatever happened in the past conforms to the government's current ideas and statements. 

In both books, the main character rebels against the conformity and regimentation imposed by the state and in both the main characters are urged on to dissent by women. In Montag's case, Clarisse encourages him to enjoy nature as well as read, and Winston has an affair with the free-spirited Julia.

The setting and atmosphere of 1984, however, is grimmer than that of Fahrenheit 451, reflecting the different circumstances in which each author found himself. 1984, which Orwell wanted to call 1948, mirrors the misery of post-war England, still rebuilding from Nazi air attacks, still rationing food, still reeling from the effects of a world war and the loss of its status as the world's premier power. In 1984, the world is relentlessly ugly. Technology, from toilets to elevators, are constantly backed up or broken, food consists of gray mystery meats and shots of gin, people wear dull overalls and life in general is bleak and pinched. 

Fahrenheit 451, however, reflects Bradbury's Californian post-war American world of booming technology and mindless consumerism. People's souls might be numb or in despair, but the technology works perhaps too effectively, narcotizing the public with mindless television shows on giant three- and four-screen TVs. 

Unlike 1984, Fahrenheit 451 ends with some hope that the individual can escape and find freedom from the state. In 1984, Winston and Julia are entirely broken: the totalitarian regime has won. The book ends, shortly before Winston is killed, with the former rebel subdued: 

"But it was all right, everything was all right, the struggle was finished. He had won the victory over himself. He loved Big Brother."