Answer:
Ominous
Explanation:
This is a tricky question, since Al Gore uses many words, and also a structure, that make his speech feel "formal". The context in which he was giving the speech does the same. But only this word, specifically, is very unfamiliar in comparison to the others used by him and this is easily substituted by an easier to understand synonym.
"We, the human species, are confronting a planetary emergency a threat to the survival of our civilization that is gathering ominous and destructive potential even as we gather here."
