Global warming will affect this -- it is full of processed cheese (3,5)
I believe the answer is:
ice sheet
'global warming will affect this' is the definition.
(ice sheets melt)
'it is full of processed cheese' is the wordplay.
'is full of' means one lot of letters goes inside another.
'processed' is an anagram indicator.
'cheese' is an anagram of 'ceshee'.
'it' going around 'ceshee' is 'ICE-SHEET'.
(Other definitions for ice sheet that I've seen before include "Extensive frozen area" , "Extensive frozen layer over land" , "white surface layer" .)