End of the fossil fuel -- reason admitted for being green (10)
I believe the answer is:
ecological
'being green' is the definition.
(I've seen this before)
'end of the fossil fuel reason admitted' is the wordplay.
'end of' suggests the final letters.
'fossil fuel' becomes 'coal' (coal is a kind of fossil fuel).
'reason' becomes 'logic' (I've seen this before**).
'admitted' is an insertion indicator.
The last letter of 'the' is 'e'.
'coal' going around 'logic' is 'cological'.
'e'+'cological'='ECOLOGICAL'
'for' is the link.
(Other definitions for ecological that I've seen before include "Gaelic cool (anag.)" , "Green" .)