Gummy atmosphere is not a literal gummy version of the atmosphere of the earth (or air). It is a metaphor, used to describe a state of mind where everything is seen in a cheerful light, and there is a certain sense of gumminess to the vibe. The phrase "gummy atmosphere" is meant to evoke a feeling of lightness, cheerfulness and happiness, without the sour or harsh notes that can sometimes be associated with the real atmosphere of earth or air.