Some adverbs refer to a whole statement and not just a part of it. They are called sentence adverbs and they act as a comment, showing the attitude or opinion of the speaker or writer to a particular situation.
Sentence adverbs often stand at the beginning of the sentence. Here are some examples:
Clearly, there have been unacceptable delays.
(= It is clear that there have been unacceptable delays.)
Sadly, the forests are now under threat.
(= It is sad that the forests are now under threat.)
Curiously, he never visited America.
(= It's curious that he never visited America.)
The sentence adverbs are used to convey the writer or speaker's opinion that it is clear/sad/curious that something happened or is the case. If you compare the way clearly, sadly, and curiously are used in the next three sentences, you can easily see the difference between the meaning of the sentence adverbs and the "ordinary" adverbs:
He spoke clearly and with conviction.
(= He spoke in a clear way and with conviction.)
She smiled sadly.
(= She smiled in a sad way.)
He looked at her curiously.
(= He looked at her in a curious/inquisitive way.)
Back to Adverbs.
Read about hopefully as a sentence adverb.