“It is virtually certain that upper ocean stratification has increased since 1970 and that sea water pH has declined globally over the last 40 years, with human influence the main driver of the observed ocean acidification (virtually certain).”
“Ocean acidification and associated reductions in the saturation state of calcium carbonate – a constituent of skeletons or shells of a variety of marine organisms – is expected to increase in the 21st century under all emissions scenarios (high confidence). There is very high confidence that present day surface pH values are unprecedented for at least 26,000 years and current rates of pH change are unprecedented since at least that time. Over the past 2–3 decades, a pH decline in the ocean interior has been observed in all ocean basins (high confidence).”
Find the full AR6 Climate Change 2021 report at: https://www.ipcc.ch/report/ar6/wg1/