Waters off the coast of California are acidifying at a much faster rate than in the rest of the world, the Los Angeles Times reports. Researchers analyzed about 2000 fossilized shells from a tiny marine creature called foraminifera, and were able to reconstruct the ocean pH for the past 100 years or so. The amount of calcium carbonate in the shells decreased by about 20% during that timeframe, signaling a 0.21 decrease in pH, the researchers report this week in Nature Geoscience. This could threaten fish and other marine animals. The scientists also found large shifts in acidification that correlated with the Pacific Decadal Oscillation, a climate pattern that could be responsible for swings in California’s rate of sea level rise. The ocean is an invaluable carbon sink, absorbing about 25% of emissions since the Industrial Revolution, and in order to slow this acidification, people will need to make some changes and curb carbon emissions.