Humans Turning Up Volume In Oceans

This week the U.S. Supreme Court gave the Navy the OK to use sonar off the coast of California — environmentalists complain the sounds confuse whales. But it turns out the planet's oceans are actually getting louder anyway. Geochemist Peter Brewer at the Monterey Bay Aquarium Research Institute talks about a recent study finding that global warming is changing the way sound travels underwater.

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ANDREA SEABROOK, host:

From NPR News, it's All Things Considered. I'm Andrea Seabrook. This week, the Supreme Court gave the U.S. Navy the OK to use sonar off the coast of California. Environmentalists complain the sounds confused whales. But it turns out, the planet's oceans are actually getting louder anyway. It's this weeks, Science Out of the Box.

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SEABROOK: It may not seem like it when you dive in, but the ocean is a pretty noisy place. And now, humans are turning up the volume.

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SEABROOK: That's according to Peter Brewer, a geochemist at the Monterey Bay Aquarium Research Institute.

Dr. PETER BREWER (Ocean Chemist, Senior Scientist, Monterey Bay Aquarium Research Institute): Well, it's an interesting geochemical story. Basically, we're putting massive amounts of carbon dioxide into the atmosphere, which everybody knows about. And, of course, it's causing global warming.

But it has some secondary effects, too. Most of the carbon dioxide we put up in the atmosphere eventually finishes up in the ocean. And as it does so, it creates a chemical change. It makes the ocean slightly more acidic, and that alters the ratio of some of the chemical ions that make up sea salt.

Some of those chemical species are responsible for sound absorption. As we change the chemistry of the ocean, some of the molecules responsible for absorbing sound in the ocean are going away.

SEABROOK: So, how much louder is the ocean today than it was, say, 100 years ago?

Dr. BREWER: Well, sound absorption has gone down by, say, 15 to 20 percent today. Now, sound transmission goes up by a larger amount. Sound transmission has probably gone up by 40 percent. So, sound would travel further.

That means whales could communicate at longer distances, and background levels of noise in the ocean will rise, the constant din of wave noise, the intrusion of shipping noise, and so on. All these things will begin to sneak up.

SEABROOK: Has anyone observed any kind of consequences that this has already had, positive or negative?

Dr. BREWER: That is difficult to say. This is such a new, interesting finding that people are searching the records now to see if there's evidence for that. We've got a complex of things going on, increasing levels of industrial noise and shipping and so on. So sorting out this change will be hard.

If you think of it, when we first began talking about global temperature changes, many people could not believe it. We'll change the planetary temperature by, say, two degrees Celsius. People say, well, it changes that much between day and night. It changes that much while you're waiting for the bus. But over the years, it becomes very clear that it's having an effect.

It's the same kind of thing here. You are dealing today with acute changes. We're describing a long-term chronic issue.

SEABROOK: If humans begin to ramp down carbon dioxide emissions or at least the increase of carbon dioxide emissions, could this be mitigated somewhat in the future? Or is the snowball already rolling, so to speak?

Dr. BREWER: Well, the snowball is already rolling. If we were to cut down emissions a great deal, things would slow down. It's very hard to get carbon dioxide back out of the ocean once it's in, although there are ways that we could think of. But the ocean is huge.

SEABROOK: Peter Brewer is a geochemist at the Monterey Bay Aquarium Research Institute. Mr. Brewer, thank you very much.

Dr. BREWER: Thank you.

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