Strictly speaking, we don't think about the future when the subject is nature because we think that it's eternal.

strictly 是形容词 strict 的副词形式，strict 意思是"严格的、精确的"，加上 -ly 变成副词表示"严格地、精确地"。 speaking 是动词 speak 的现在分词形式，speak 意思是"说话、表达"。 strictly speaking 是一个固定搭配，意思是"严格来说、准确地说"，用于引出更精确或更正式的说法。