But the real truth is that we don't know enough to relieve global warming,and-without major technological breakthroughs-we can't do much about it. (08.6 Passage 1)
分析主干:the (real) truth is that...
that 引导的是一个表语从句.该从句本身是两个由and 并列连接的分句.破折号中的内容是插入语,起解释说明的作用,表示前提条件:“如果没有技术上的突破”。