Greenhouse gas (6,7)
'greenhouse gas' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for methane that I've seen before include "Greenhouse gas produced by cows" , "Naturally occurring flammable gas" , "Main constituent of natural gas" , "Combustible atmosphere" , "contributor to global warming" .)
'greenhouse gas' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for carbon dioxide that I've seen before include "Gas produced in breathing" , "Gas for dry ice" , "Gas formed by breathing out" , "gas from exhaust?" , "Gas breathed out" .)