The world’s oceans have absorbed roughly half the carbon dioxide emitted by human activities since pre-industrial times. But today, the rate of the greenhouse gas CO2  dissolving from the atmosphere into seawater is exceeding the ocean’s natural buffering capacity. As a result, “The waters of the upper ocean are now undergoing an extraordinary transition in their fundamental chemical state at a rate not seen on Earth for millions of years,” state scientists at the Monterey Bay Aquarium Research Institute (MBARI) in Geophysical Research Letters.

A recent Royal Society report notes that the resulting formation of carbonic acid makes it more difficult for sea life like corals and starfish to form shells and skeletons. More, endangered reefs increase tropical islands’ vulnerability to storms.

MBARI also estimates “that sound already may travel 10 percent farther in the oceans than it did a few hundred years ago,” and may travel as much as 70 percent farther by mid-century. Seawater acidity favors transmission of low- to mid-frequency sounds; this has unknown consequences for marine mammals that rely on sound to communicate and to find food and mates.

“Ocean acidification is likely to have an ecological cascade effect right up to parts of the food web that are important to human beings, such as fish and shellfish,” says Dr. Will Howard, of the Antarctic Climate & Ecosystems Cooperative Research Centre.