Key climate changee effects on the coastal and marine environment around the Indian Ocean UK Overseas Territories

A climate-change baseline and climate-change impacts of the highest priority were identified for the British Indian Ocean Territory (BIOT) by scientists with relevant expertise along with managers responsible for the area. •Four priority climate-change issues were identified for BIOT: 1. Changes in coral species 2. Changes in coral reefs (reef carbonate structure and the living reef ecosystem)3. Changes in reef islands and sandy beaches4. Impacts on the provision of natural coastal protection andand island resilience to sea-level rise.•All projections of future climate change suggest that severity and frequency of destructive ocean heatwaves will increase. Eighteen years ago, the ‘extinction point’ for reefs in the Chagos Archipelago was predicted to be in the early 2020s, and evidence suggests that the likelihood is increasing, based on presentobservations and the implication of climate-change projections on coral reefs in the Indian Ocean region. •As a fully protected Marine Protected Area (MPA) in a remote location, BIOT provides aglobally important reference site for climate change impacts that can give insights into finer-scale vulnerability and resilience in the absence of other anthropogenic stressors. Research to date has demonstrated the value of BIOT as an ocean observatory.•Restoration of island ecosystems through the eradication of invasive rats, and restoration of native vegetation, is the quickest and most effective way to restore seabird populations and the associated nutrient pathways that build resilience against climate-change impacts in the marine environment. •At a local level, theBIOT administration should implement any possible greenhouse gas reduction measures on the inhabited island of Diego Garcia and minimise stressors to the BIOT MPA. At a global level,the UK government must continue to demonstrate leadership in the immediate reduction of greenhouse gas emissions and meet and then exceed targets set in the Paris Agreement. COP26 will be instrumental in defining the pathway for the planet and any future for coral reefs in BIOT and elsewhere.