The world is abuzz with climate change - in more ways than one. Swelling waves and rising sea levels can be detected in the way the planet "hums", says an oceanographer.

Peter Bromirski, of the Scripps Institution of Oceanography at the University of California, San Diego, says that seismic listening stations provide a long-term record of how the amount of energy reaching the world's shores is changing with climate change.

Most geologists who study seismology try to eliminate background noise in their data, but a handful of researchers have started to take a closer look at it.

They have identified at least three different types of "noise", including the Earth's hum, which was first discovered in 1998. The other two are called "microseisms" - tiny earthquakes - and have slightly different acoustic properties.

Noisy planet

Both the hum and microseisms are triggered by waves thumping the Earth's crust, so if waves change, geologists should be able to "hear" it. Bigger waves cause higher amplitude microseisms and hum, says Bromirski. This roughly translates to a louder noise in the seismological data.

"Onshore measurements of microseisms track wave height offshore reasonably well," agrees Spahr Webb of Columbia University's Earth Institute.

In some locations, seismograms have been faithfully recording every shake in the Earth's crust for nearly a century, meaning geologists can dissect what Bromirski calls the "treasure trove" of archived paper drums - and find out how ocean waves have changed over the last 100 years.

"The calibrated seismometer records go back further than do good wave measuring systems," adds Webb.

Stormy weather

This may all seem academic, but bigger waves carry more energy. As a result, the century-long record of hum and microseisms can reveal how much of a pounding coasts have experienced, and could help predict how much more pounding they can expect.

"This is important from coastal erosion and shoreline change perspectives under rising sea levels," says Bromirski.

Journal reference: Science, DOI: link (in press)