ocean acidification has driven mass extinction events a number of times in the past. It played a major role in the last extinction event, 66 million years ago, when ocean pH dropped by 0.25. That small shift was enough to wipe out 75% of marine species. On our present emissions trajectory, ocean pH will drop by 0.4 by the end of the century.16 We know what’s about to happen. We can see it coming. In fact, it’s already beginning to play out in real time: marine animals are disappearing at twice the rate that land animals are.
