What does global warming sound like? Scientists may have just found that out. They've recorded and identified the sizzle of glacier ice as it melts into the sea. The noise, caused by trapped air bubbles squirting out of the disappearing ice, could provide clues to the rate of glacier melt and help researchers better monitor fast-changing polar environments.

If you kayak in the frigid northern waters near glaciers, you can hear the popping, crackling sounds of the melting ice. Yet these noises are also picked up by underwater microphones at a much louder volume than above the surface.

"If you were underneath the water in a complete downpour, with the rain pounding the water, that's one of the loudest natural ocean sounds out there," said Erin Pettit, one of the researchers, in a news release. "In glacial fjords we record that level of sound almost continually."

Although the researchers assumed that the noise picked up by their microphones was the sound of melting ice, they needed to confirm the theory. They mounted chunks of glacier in a tank of chilled water and then recorded video and audio of the ice as it melted. This allowed them to confirm that the sounds they were hearing were the escape of bubbles from the ice.

"Most of the sound comes from the bubbles oscillating when they're ejected," said Kevin Lee, one of the researchers, in a news release. "A bubble when it is released from a nozzle or any orifice will naturally oscillate at a frequency that's inversely proportional to the radius of the bubble." This means that the smaller the bubble, the higher the pitch. In this case, the scientists recorded sounds in the 1-3 kilohertz range, which is right in the middle of the frequencies that humans hear.

The findings reveal how sound can play an important role in monitoring glacier melt. While the symphony of melting ice might not carry the same impact as images, it still has its own story to tell. It's possible that hydrophone recordings could be used in glacial fjords to monitor relative changes in glacier melting in response to one-time weather events, seasonal changes and long-term climate trends.

The abstract describing the work can be found online here.