 Coral reefs provide food and habitat for a wide range of organisms and ecological goods and services. Warmwater coral reefs occupy shallow sunlit waters to grow and calcify at high rates, while mesophotic coral reefs accumulate calcium carbonate at lower rates in deeper locations. Coldwater coral reefs are found in the dark depths. Coral reefs face significant challenges from human activities such as pollution, over-harvesting, physical destruction, and climate climate change. Climate change is likely to drive the elimination of most warmwater coral reefs by 2040 to 2050, while coldwater corals are threatened by warming temperatures and ocean acidification. Evidence that coral reefs can adapt at rates sufficient for them to keep up with rapid ocean warming and acidification is minimal. Coral reefs are likely to degrade rapidly over the next 20 years, presenting fundamental challenges for the 500 million people who derive food, income, coastal protection, and a range of other services from coral reefs. Unless rapid advances to the goals of the Paris Climate Change Agreement occur over the next decade, hundreds of millions of people are likely to face increasing amounts of poverty and social disruption, and, in some cases, regional insecurity.