The mood of "To Build a Fire" is initially lonely and bleak, with London's imagery emphasizing the man's isolation and the harshness of the landscape. The story consistently draws attention to the fact that no one has traveled on this path for quite some time and that the man, who is no longer following the main Yukon Trail, is completely cut off from civilization:
The furrow of the old sled-trail was plainly visible, but a dozen inches of snow covered the marks of the last runners. In a month no man had come up or down that silent creek.
The mood of the story is also somewhat foreboding. As the man travels, London directs the reader's attention to the hidden pools of water beneath the ice, hinting that something awful will befall him. At the beginning of the story, London also comments on the gloomy atmosphere:
It was a clear day, and yet there seemed an intangible pall over the face of things, a subtle gloom that made the day dark, and that was due to the absence of sun.
At the story's climax, the mood becomes tense and frantic. As the man struggles to build a fire and save himself, London's sentences build in momentum, and the reader can feel the man's physical and mental desperation:
He began threshing his arms back and forth, beating the mittened hands against his sides. He did this for five minutes, violently, and his heart pumped enough blood up to the surface to put a stop to his shivering... A certain fear of death, dull and oppressive, came to him. This fear quickly became poignant as he realized that it was no longer a mere matter of freezing his fingers and toes, or of losing his hands and feet, but that it was a matter of life and death with the chances against him.
Literary Realism sought to accurately depict the experiences of ordinary people, and London's vivid, unflinching descriptions of the man's panic are starkly realistic. The mood of the text inspires emotions of fear and desperation in the reader, prompting them to identify with the man and illustrating how universal these emotions are.
