One might be worried to see lost ice go! (9)
I believe the answer is:
ecologist
'one might' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'worried to see lost ice go' is the wordplay.
'lost ice go' can be anagrammed to 'ECOLOGIST'.
Though, I am unsure how the anagram is indicated.
'be' acts as a link.
Can you help me to learn more?
(Other definitions for ecologist that I've seen before include "See scientist" , "One concerned with the environment" , "Student of living things and their environment" , "Company's possessions" , "Environmentalist" .)