At last climate denier wobbles, being less secure (7)
I believe the answer is:
needier
'less secure' is the definition.
(needy can mean insecure or vulnerable)
'at last climate denier wobbles' is the wordplay.
'at last' indicates one should take the final letters.
'wobbles' is an anagram indicator (I've seen 'wobbling' mean this).
The last letter of 'climate' is 'e'.
'e'+'denier'='edenier'
'edenier' anagrammed gives 'NEEDIER'.
'being' is the link.
(Other definitions for needier that I've seen before include "Wanting more" , "Poorer" , "Less well off" , "more impoverished" , "More disadvantaged" .)