Some semantic interpretations:
Consider the etymology of the word “crisis” found in Etymonline
early 15c., crise, crisis, "decisive point in the progress of a disease," also "vitally important or decisive state of things, point at which change must come, for better or worse," from Latinized form of Greek krisis "turning point in a disease, that change which indicates recovery or death" (used as such by Hippocrates and Galen), literally "judgment, result of a trial, selection," from krinein "to separate, decide, judge," from PIE root *krei- "to sieve," thus "discriminate, distinguish."
Reflect on the aptness of the etymology of this word when discussing the climate crisis.
Some orthographic investigations:
This word has a final, single, final <s> and is not a plural. There is a convention that complete English words that could be a plural avoid looking like a plural if they are not. There are a number of orthographic conventions that have evolved for “plural canceling”. One is doubling a final <s> (e.g. <business>, <glass>). Another is using the orthographic marker <e> as a plural cancelling marker (See Venezky, 1999). That explains the final, non-syllabic <e> in words like <please>, <house> and countless other words.
Any hypotheses why <crisis> does not have a plural canceling marker <e>? (Hint, note the first historical root (in italics in Etymonline) is crisis.