Presence of two verbs

This sentences have taken from CAMBRIDGE
IELTS
4.

“Disenchantment with orthodox medicine has
seen the popularity of alternative therapies in
Australia climb steadily during the past 20
years.”

I think, here ‘climb’ is acting as a verb. Am I
right? What is the subject of this verb?
“Disenchantment with orthodox medicine has
seen the popularity of alternative therapies in
Australia” is able to make a full sense. It is
impossible for a sentence to have more than one
verb. How this sentence contains two verb?
Would you like to clear the meaning of this given
sentence? If it is possible to you, please provide
me many examples/lesson related to the
structure of this sentence.

In in a bit of a rush so I can’t explain it thoroughly right now, but a sentence can have any number of verbs, and the subject of “climb” in this case is “the popularity of alternative therapies”.