Either we invest in renewable energy, which scientists believe is essential for reducing emissions, or we will face a climate crisis that future generations cannot escape.

either...or 连接两个长分句，第一个分句嵌入 which 引导的非限制性定语从句说明可再生能源的重要性，第二个分句嵌入 that 引导的限制性定语从句说明气候危机的不可避免性，展示 C1 级关联连词如何串联多层嵌入结构。