rapid climb vs ascension

rapid climb and ascension both are nouns.

Word	Noun	Adjective	Verb	Adverb
rapid climb	Yes	No	No	No
ascension	Yes	No	No	No

As nouns, ascension is a hypernym of rapid climb; that is, ascension is a word with a broader meaning than rapid climb:

Other hypernyms of rapid climb include ascent, rise, rising.

rapid climb (noun)	ascension (noun)
a rapid rise	the act of changing location in an upward direction
	a movement upward; rise above the ground
	(astronomy) the rising of a star above the horizon