Upsetting encyclopedic oceanological study reveals environmental destruction (7)
I believe the answer is:
ecocide
'environmental destruction' is the definition.
(I've seen this in another clue)
'upsetting encyclopedic oceanological study reveals' is the wordplay.
'upsetting' says the letters should be written in reverse.
'reveals' says the answer is hidden in the clue.
'edicoce' can be found hidden inside 'encyclopedic oceanological study'.
'edicoce' back-to-front is 'ECOCIDE'.
(Other definitions for ecocide that I've seen before include "Deliberate destruction of the environment" , "Destruction of the natural environment" , "Environmental ruin" .)