The atmosphere belongs to the part of speech known as a noun. It is a noun because it refers to a specific entity or concept, which in this case is the layer of gases surrounding the Earth. The atmosphere is a tangible and identifiable entity, and as such, it fits the definition of a noun.

The atmosphere is often described as a noun because it is a physical entity that can be studied and measured. For instance, the National Oceanic and Atmospheric Administration (NOAA) is an organization that focuses on studying and monitoring the atmosphere, including weather patterns, climate change, and atmospheric composition. The term "atmosphere" is used as a subject in sentences, such as "The atmosphere is changing due to global warming," indicating its status as a noun.

Data from the Intergovernmental Panel on Climate Change (IPCC) supports the classification of the atmosphere as a noun. The IPCC reports provide extensive research on the Earth's atmosphere, including its composition, the impact of human activities on it, and the potential consequences of these changes. The use of the term "atmosphere" in these reports as a subject or object in sentences further reinforces its status as a noun. For example, the IPCC's Fifth Assessment Report states, "The atmosphere has warmed by approximately 0.85°C since 1870," demonstrating the use of "atmosphere" as a noun in a scientific context.