这就说明认为such+名词+as+从句中，as都是关系代词引导定语从句的分析是错误的。因为as在从句中不仅仅作主语、宾语、或表语，还可以作状语。

本质上，as引导的仍然是比较分句，such...as...意为像...这样的...，是比较意义。

你的句子中，如果用the替换such, as就必须改为when引导定语从句。由此你就知道本句中的as并不是关系代词，而是呼应such的比较副词。

Until such time as mankind has the sense to lower its population to the point where the planet can provide a comfortable support for all, people will have to accept more unnatural food. (as引导比较分句，呼应such.)

Until the time when mankind has the sense to lower its population to the point where the planet can provide a comfortable support for all, people will have to accept more unnatural food. (when引导关系分句修饰the time.)