Act gloomily, troubled by this study of global warming etc? (11)
I believe the answer is:
climatology
'this study of global warming etc?' is the definition.
(climatologists study the world's climate)
'act gloomily troubled' is the wordplay.
'troubled' indicates anagramming the letters.
'act'+'gloomily'='actgloomily'
'actgloomily' is an anagram of 'CLIMATOLOGY'.
'by' acts as a link.
(Other definitions for climatology that I've seen before include "Study of long-term weather" , "Study of conditions" .)