It seems that most of the heat impact of global warming is absorbed by ocean waters (https://e360.yale.edu/features/how_long_can_oceans_continue_...) Coral reefs typically live in rather shallow waters (less than 500ft according to wikipedia), because of their dependency of sunlight. So at this depth, there is already a strong daily variation due to day/night cycle, and I imagine a 1 degree average warming on earth is much potentiated in this environment.

Perhaps there is something to be done actively in short term in those environments to prevent this warming, but its so fragile as there are countless interactions between all the microorganisms that I that must be an enormous undertaking, if even possible.