Note the world shortage (6)
I believe the answer is:
dearth
'shortage' is the definition.
(dearth can mean a shortage or lack)
'note the world' is the wordplay.
'note' becomes 'D' (musical note).
'the world' becomes 'Earth' (synonyms).
'd'+'earth'='DEARTH'
(Other definitions for dearth that I've seen before include "Scarceness or lack" , "deficiency" , "Severe lack" , "Hatred (anag) -- shortage" , "poverty" .)