In this sentence " even" is a comparative adverb making hotter have a more intense meaning.

在这个句子中，even是一个比较级副词，使hotter的语义更强烈。

A comparative adverb clause with a subject and a verb.

带有主语和动词的比较级副词从句。

There are all sorts of subcategories too, like singular vs. plural nouns and superlative vs. comparative adverbs, but we’re not going to get into that.

还有各种各样的子类别，例如单数名词与复数名词以及最高级与比较副词，但我们不打算深入探讨。