139. Read the following passage, then answer the question below.

Oceans have absorbed roughly a quarter of the carbon dioxide that humans have released since the Industrial Revolution, which has slowed the pace of climate change on land. But the benefit comes at a cost. When carbon dioxide dissolves in seawater, it forms carbonic acid, and the surface ocean has become about thirty percent more acidic than it was two centuries ago.

The change is small in absolute terms, since the ocean remains slightly alkaline, but chemistry matters at the margins. Many marine organisms build shells or skeletons from calcium carbonate, which dissolves more readily in acidic water. In laboratory experiments, young oysters raised in acidified water produced thinner shells and grew more slowly, and commercial hatcheries on the Pacific coast of North America lost large numbers of larvae in the early 2000s before adjusting their water chemistry. Pteropods, tiny swimming snails that feed salmon and other fish, show shell damage in the Southern Ocean.

Scientists caution against assuming that every species will suffer. Some algae and seagrasses may benefit from extra carbon dioxide, and certain fish appear resilient. Yet ecosystems are not merely collections of species. If a key link in a food chain declines, the effects can spread to species that are not directly sensitive to acidity. For this reason, researchers are cautious about predicting winners and losers.

Unlike warming, acidification cannot be reversed in human timescales even if emissions stopped, because the ocean takes thousands of years to neutralize the added acid by dissolving rock. This lengthy recovery is why many scientists argue that cutting emissions, rather than adapting to ocean chemistry, remains the only effective response.

Why does the author mention that the ocean takes thousands of years to neutralize the added acid?