This is the adjective clause, because Severe is describing the arctic. Therefore, it’s a adjective, and the surrounding words would make it an adjective clause
Adjective clauses are clauses modifying, describing or giving more information about nouns. We can identify them because they are usually placed right next to the noun they describe, and beginning with a relative pronoun (<em>who, whom, whose, that </em>or<em> </em><u><em>which</em></u>) or a relative adverb (<em>when, where </em>or<em> why</em>). In the sentence, “Which is very severe in the Arctic” is the adjective clause because it describes and gives us information about the noun “The weather.”
The word "were" isn't a coordinating conjunction because it simply isn't able to connect two independent clauses and put them together to form a compound sentence.
