This document provides information about ocean acidification and its threats to marine life. It discusses how ocean acidification is caused by carbon dioxide absorption from the atmosphere. This lowered pH makes it difficult for calcifying organisms like corals, shellfish, and plankton to build their shells and structures. The passage notes that ocean pH has dropped by 0.1 units since the Industrial Revolution and could decline by 0.45 more units by 2100. This threatens ocean ecosystems and is another reason to reduce fossil fuel emissions.