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? the subject of the verb is "the popularity of alternative therapies"
How this sentence contains two verb? of course there can be endless verb in a sentence. For example, "I saw him climb the stairs as I woke up and opened the door to..." now to is an infinitive. Put any verb after that to make the sentence longer.
And to simplify the sentence , "Australia is so tired of orthodox medicine, alternative therapies have started to increase there in the last 20 years."