a phenomenon that most scientists agree (that the phenomenon) is caused by human begins' burning of fossil fuels. 说的that most scientists agree既是前面的定语,又引导了后面的从句。
但我觉得,难道that most scientists agree不能只做a phenomenon的定语从句吗?那么这就是个限制性定语从句, a house that most costomers like is bought by sb. 等于that most scientists agree是限定a phenomenon的,是一个现象,什么现象呢?大部分科学家都同意的现象。这个大部分科学家都同意的现象是由于什么引起的。