One of the tactics London uses in "To Build a Fire" is dramatic irony. At the beginning of the story, he states that while the man believes the temperature to be about 50 degrees below zero, the dog better understands just how cold it is.
The animal was depressed by the tremendous cold. It knew that it was no time for travelling. Its instinct told it a truer tale than was told to the man by the man’s judgment. In reality, it was not merely colder than fifty below zero; it was colder than sixty below, than seventy below. It was seventy-five below zero.
At this point, the reader possesses knowledge that the man does not and better understands the danger of traveling in such weather. There's an acute sense of danger and impending doom, but the man doesn't seem all that aware of the trouble he's in. Readers therefore end up feeling somewhat aligned with the man's dog, since the dog instinctually understands the gravity of the situation. This use of dramatic irony highlights the man's lack of experience when it comes to traveling in the Yukon, and it also underscores the unreliability of his judgement, which is in direct contrast to the accuracy of the dog's instinct.
