Shelter engulfed by river: global warming? (7)
I believe the answer is:
detente
'global warming?' is the definition.
(I've seen this in another clue)
'shelter engulfed by river' is the wordplay.
'shelter' becomes 'tent' (canvas shelter).
'engulfed by' means one lot of letters goes inside another.
'river' becomes 'dee' (River Dee).
'tent' going within 'dee' is 'DETENTE'.
(Other definitions for detente that I've seen before include "Thaw in relations" , "relaxation" , "The easing of tensions between nations" , "Easing of hostilities" , "Easing of hostility between countries" .)