In an essay that talks about ways to reduce carbon dioxide maps would most likely be used as

Expository

Explanation:

Essays are categorized in many different forms these are:

Narrative: tells a story from the viewpoint of one of the characters in the story. Here they describe the sights and sounds of the things around as well as the feelings and thought of the characters.Descriptive: Deeply discusses characters and traits of a scene or a person. This type of essay is full of descriptive words that are highly sensory. The are often objective and offer the reading with an absolute perspective of the environment. Expository: These go deeply into specific issues and explain them. The also discuss a problem and may offer solutions to them. Argumentative: These not only discuss an issue but they choose a position on that issue and give reasons why in order to convince a reader.

In conclusion, if this essay is describing ways to reduce carbon dioxide maps it is most likely an expository essay.