A new study suggests that by 2050, most coral reefs around the world are at risk of experiencing constant depletion of one of their building blocks - calcium carbonate sediments. A few reefs are already experiencing this state, called net sediment dissolution, which greatly hinders the growth of coral reefs and consequently impacts the health and biodiversity of reef habitats. The results of this study better reveal how intensifying human-made carbon dioxide absorption, or ocean acidification, will affect one of two processes important to coral survival. Surface seawaters where coral reefs reside normally have sufficiently high concentrations of dissolved carbonate for corals to calcify their hard skeletons. Human-made ocean acidification has been linked to lower levels of calcium carbonate saturation and is therefore expected to reduce coral building rates; however, scientists have yet to uncover how ocean acidification will affect another process important to corals, the dissolving of coral reef calcium carbonate sediments, which accumulate over thousands of years and can be the major repository of calcium carbonate in modern coral reefs. Now, by measuring calcium carbonate dissolution at various reef locations in the Pacific and Atlantic Oceans, Bradley Eyre and colleagues discovered a stronger correlation between sediment dissolution and ocean acidification than between acidification and coral calcification. In fact, they found an average reduction in coral calcification since pre-industrial times. In their studies, four out of 22 reefs have already experienced average seawater conditions that would promote net sediment dissolution, they report, and given the current rate of acidification, all but two reefs across the three ocean basins should experience net dissolution by the end of the century, the authors predict. Other climate change induced factors such as increased sea surface temperature and coral bleaching will likely accelerate the loss of coral reefs, they add.