Clue: Terrible mistake detailed about one reaching end of game, extreme temperatures — with this? (7,6)
Answer: CLIMATE CHANGE
Explanation: Definition: with this?
**CLANGE**[r]="Terrible mistake", de-tailed with the final letter removed; around all of: **I**="one" plus **MATE**="end of [chess] game" plus **C**+**H**=Cold and Hot="extreme temperatures"