Sounding challenge to mountaineer, money serious current issue (7,6)
I believe the answer is:
climate change
'serious current issue' is the definition.
(global issue)
'sounding challenge to mountaineer money' is the wordplay.
'sounding' shows a homophone (sound like).
'challenge to mountaineer' becomes 'climb it' (challenge to climb a mountain).
'money' becomes 'change' (I've seen this in other clues).
'climbit' is a homophone of 'climate'.
'climate'+'change'='CLIMATE CHANGE'
(Other definitions for climate change that I've seen before include "Effect of 1" , "global warming" .)