EXPLANATION Conjunctions (from con = with and jungo = to join) join grammatical units. Coordinating conjunctions (and, but) join the same sorts of clauses (e.g. two simple sentences or two adjectival clauses). Subordinating conjunctions (because, as, if...) introduce subordinate adverbial clauses. Conjunctive adverbs are adverbs that can also fulfil a joining function. Typically, adverbs modify verbs, adjectives and other adverbs. Conjunctive adverbs, however, join two independent clauses together, the second clause modifying the first clause in some way. Some adverbs that commonly function this way are: additionally, besides, however, contrariwise, furthermore, moreover, nevertheless, nonetheless, otherwise, similarly, conversely.
Because conjunctive adverbs introduce sentences that are closely related to the sentences that precede them, the use of a semicolon before conjunctive adverbs helps to imply this close relationship.
Another option is to finish the initial sentence with a full stop and then to start the new sentence with a capital letter. A comma is not appropriate - especially as sometimes the adverb could be the last word of the previous sentence.