Mat crawling with lice, suggesting a worrying trend? (7,6)
I believe the answer is:
climate change
'worrying trend?' is the definition.
'mat crawling with lice suggesting a' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'an' and 'an' is found within the answer.
This explanation may well be incorrect...
(Other definitions for climate change that I've seen before include "Effect of 1" , "global warming" .)