Since the Industrial Revolution, the ocean has absorbed approximately 30 percent of anthropogenic CO2 emissions. While this has slowed atmospheric warming, it has fundamentally altered ocean chemistry. Surface ocean pH has decreased by 0.1 units — a 26 percent increase in acidity. This threatens organisms that build calcium carbonate shells and skeletons, including corals, mollusks, and certain plankton species. Models project a further decrease of 0.3-0.4 pH units by 2100 under high-emission scenarios.