This article originally appeared on VICE Netherlands.
In five to ten years, scientists might be using microphones to measure climate change. Research conducted by Läslo Evers, head of R&D at the Seismology and Acoustics department of the Royal Netherlands Meteorological Institute, shows how a relatively simple instrument can measure the pressure waves created by infrasounds hundreds of kilometres away.
Infrasound is all sound under 20 hertz, or 20 sound waves per second. Humans can't hear it, but it's the sound that elephants make to communicate – and glaciers make when they melt. By measuring the speed of these sound waves, scientists can determine deep sea and high atmosphere temperatures. They can also calculate the pace of the ice melting by listening in for an increase in the sound generated by all the glaciers in the area over a set period of time.
For his PhD thesis, Evers used acoustic tech from the Cold War era (when infrasound microphones were installed all over the globe to detect illegal nuclear tests) to develop an innovative device able to register sudden loud noises, or "spikes". By averaging measurements from different stations and sprinkling in a bit of maths, scientists can tell the temperature in hard-to-reach areas of the world.
Evers' research isn't well known both inside or outside of the climate science community, because it's – as he describes it – a "new area of expertise". But besides its potential contribution to climate science, the device has recorded exceptional events, like a giant meteor explosion above the Bering Sea. Last year, Evers even wrote a paper about how infrasound could help passively and remotely monitor missile launches in North Korea.
I met with him to learn more about how this technology works.
VICE: In your research, you write that this instrument can measure glaciers melting using infrasound. Have you found anything interesting you can share with us?
Läslo Evers: Well, this isn't 100 percent sure yet, but what we seem to observe is that the amount of acoustic waves is narrowly related to the pace of the melting. If we can figure out how the acoustics and the melting relate one to one, we can monitor how quickly the ice melts in places that are difficult to measure.
How have glacier specialists responded to all of this?
They're excited. One of the arrays [the acoustic device used to measure the distance of the source of the sound] is in a bay in Greenland, close to a bunch of glaciers. Because it is an array [and it can measure distances], we can tune in to different glaciers in a 30 to 40-kilometre radius and detect the average increase in sound. From there, we can figure out the average rate of melting.
This instrument can measure temperature based on a "medium", which can be both air and water. Can you explain what it means?
Yes, so the microbarometer can measure the temperature of both water and air. If the medium is warm, sound travels faster than when it's cold. By using different measuring stations at the same time, the speed of sound can pretty accurately tell the temperature. This is easiest when there is a constant source of sound.
Why is that?
For example, we did a study with a volcano on Kamchatka that had been erupting for almost a year, so we knew the sound was a constant. This constant sound source becomes our input to then make observations about either the atmosphere or the ocean. And that’s very interesting, because you can make measurements in parts of the atmosphere that are never measured. So you can, just by listening, get an idea of a higher layer of our atmosphere. That’s incredible!
And it works the same way in the deepest parts of the ocean?
We’re actually beyond that. If you depend on a source of sound [like an underwater eruption], you always have to wait for something to explode somewhere. We’re at the point now where we can figure out the temperature of the deep sea just by looking at the ambient noise caught by the different arrays. So just by listening, you can pinpoint the speed of the ambient noise, and through that, the temperature.
How accurately can you measure the temperature in the deep seas?
At the moment, we are accurate to the decimal. To measure global warming more exactly, we need to become even more accurate.
How do you do that?
By measuring with more microphones. If you have more data, you can increase the accuracy. We’re experimenting with that right now. And there’s some math involved too, of course.
Are climate scientists starting to connect with your research?
We’re just beginning to enter that world, mostly through academic citations and by sharing our story at conventions. You have to talk to each other, because you speak a different language. Once enough people have learned about acoustics, I think we can really make a big contribution to measuring the temperatures in the deep sea and the high atmosphere, because at the moment we know very little about how these areas influence the weather and our climate.