somberness vs sobriety

somberness and sobriety both are nouns.

Word	Noun	Adjective	Verb	Adverb
somberness	Yes	No	No	No
sobriety	Yes	No	No	No

As nouns, somberness and sobriety are synonyms defined as:

Other synonyms of somberness include graveness, gravity, soberness, sombreness.

somberness (noun)	sobriety (noun)
a manner that is serious and solemn	abstaining from excess
a feeling of melancholy apprehension	a manner that is serious and solemn
a state of partial or total darkness	moderation in or abstinence from alcohol or other drugs
	the state of being sober and not intoxicated by alcohol