evidence: This added CO2 has had significant effects on the ocean. Surface waters are now 30 percent more acidic than they were at the start of the industrial era. Ocean acidification is now happening at a faster rate than at any point in the last 66 million years, and possibly in the last 300 million years. And projections show that by the end of this century, ocean surface waters could be more than twice as acidic as they were at the end of last century if we do not reduce our carbon emissions. [...] Ocean acidification is particularly detrimental to species that build their skeletons and shells from calcium carbonate (like clams, mussels, crabs, phytoplankton, and corals), and that constitute the bottom of the food chain. Acidification reduces the availability of carbonate ions in ocean water, which provide the building blocks these organisms need to make their shells and skeletons, significantly reducing the chances for their offspring to survive. [...] If CO2 emissions continue unabated, by the end of the century, ocean acidification is expected to reduce harvests of U.S. shellfish. It’s estimated that by the end of the century annual supplies of clams could decrease by 35 percent, oysters supplies could fall by 50 percent, and scallops could see a decline of 55 percent. Overall, the shellfish industry could experience cumulative consumer losses of $230 million. In this same scenario, ocean acidification paired with warming could cost $140 billion in today’s dollars in lost recreational benefits associated with coral reefs, and the US coral reef recreation industry could decline in value by more than 90 percent by 2100.