 Coral reefs provide food and habitat for a wide range of organisms and ecological goods and services. Warm water coral reefs are found in shallow sunlit waters to grow and calcify at high rates, while mesophotic coral reefs accumulate calcium carbonate at lower rates but remain important as habitat. Cold water coral reefs are found in the dark depths. Coral reefs face significant challenges from human activities including pollution, over-harvesting, physical destruction and climate change. Climate change is likely to drive the elimination of most warm water coral reefs by 2040-2050 due to rising ocean temperatures and acidification. Evidence that coral reefs can adapt at sufficient rates to keep up with rapid ocean warming and acidification is minimal and corals are long lived with slow rates of evolution. 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 other services from them. Unless rapid advances to the goals of the Paris Climate Change Agreement occur over the next decade, hundreds of millions of people may face poverty, social disruption and regional insecurity. This article was authored by Ove Hegg Goldberg, Ove Hegg Goldberg, Ove Hegg Goldberg and others.