CO2 could worsen whales' sonar problems

On Wednesday, the US Supreme Court heard a dispute between a group of conservationists and the Navy over sonar exercises that scientists say are killing and injuring whales. What isn't often mentioned in the debate is how the burning of fossil fuels could be making the problem worse.

It's not mentioned because the discovery of the connection was published only last week. Scientists have long known that increased carbon dioxide in the atmosphere causes ocean acidification, and they have also known that the amount of sound that can be absorbed by seawater partly depends on the water's pH. But nobody thought to combine these two phenomena until ocean chemists Peter Brewer, Keith Hester, and their colleagues at the Monterey Bay Aquarium Research Institute came along.

Their paper, "Unanticipated consequences of ocean acidification: A noisier ocean at lower pH," published last week in the journal Geophysical Research Letters, found that fossil fuels are turning up the ocean's volume. Since the beginning of the Industrial Revolution, the overall pH of the world's oceans has dropped by about 0.1 units, with more of the changes concentrated closer to the poles. The authors found that sound absorption has decreased by 15 percent in parts of the North Atlantic and by 10 percent throughout the Atlantic and Pacific

As Discovery News notes, these values are probably underestimated because they are based only on atmospheric CO2 absorbed into the ocean, and not on any other factors that could increase the acidity of the seawater.

And unless we curb our fossil fuel use, it's only going to get louder down there. The Intergovernmental Panel on Climate Change concluded that unless carbon dioxide emissions are curbed, the ocean's pH will drop about another 0.3 points by midcentury. This increase in acidity, say the authors, could decrease absorption by almost 40 percent, and sound could travel up to 70 percent farther.

In their abstract, the authors conclude: "Ambient noise levels in the ocean within the auditory range critical for environmental, military, and economic interests are set to increase significantly due to the combined effects of decreased absorption and increasing sources from mankind's activities."

Or, as a humpback whale might put it, "What? I can't hear you!"