The GBR is already severely impacted by climate change, particularly ocean warming, through more frequent and severe coral bleaching  . The worst coral bleaching event on record affected over 90% of reefs in 2016 . In the most northern 700-km-long section of the GBR in which the heat exposure was the most extreme, 50% of the coral cover on reef crests was lost within 8 months . Throughout the entire GBR, including the southern third where heat exposure was minimal, the cover of corals declined by 30% between March and November 2016 . In 2017, the central third of the reef was the most severely affected and the back-to-back regional-scale bleaching events has led to an unprecedented shift in the composition of GBR coral assemblages, transforming the northern and middle sections of the reef system  to a highly degraded state . Coral recruitment to the GBR in 2018 was reduced to only 11% of the long-term average . A mass bleaching event also occurred in 2020, making it the third event in 5 years  .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report