Increased absorption of CO2 by seawater changes how sound travels. Which in turn affects how whales communicate.
Research published last week in Geophysical Research Letters studied the relationship between audio absorption and ocean pH. In their paper "“Unanticipated consequences of ocean acidification: A noisier ocean at lower pH,” ocean chemists Peter Brewer, Keith Hester, and other researchers at the Monterey Bay Aquarium Research Institute report that, since the Industrial Revolution, as sea pH has decreased and become more acidic, sound absorption has decreased by 15 percent in parts of the North
Atlantic and by 10 percent throughout the Atlantic and Pacific.
In other words, whales and other creatures which communicate via sounds traveling through seawater will have increasing trouble hearing each other, as the pH continues to decrease with increasing output of fossil fuels into the atmosphere.