About GHG.EARTH

Last modified: 23 January 2017

GHG.EARTH makes sound of climate change.

GHG.EARTH is a sonification of the most recent atmospheric CO₂ reading at Mauna Loa in Hawaii at the observatory run by the United States National Oceanic and Atmospheric Administration. This is where the Keeling Curve comes from.

GHG.EARTH is meant as background, ambient music. Play it at a low volume while you do other things. The next day the sound will be a little different. The day after that, a little different again. Next year, it will be higher. The year after, higher still.

The current composition comes from Matt Diamond’s Javascript Drone.

How it works

Sound and Hz

Sounds come to us as vibrations in the air. According to Wikipedia’s hearing range article, the “human range is commonly given as 20 to 20,000 Hz, though there is considerable variation between individuals.” Hz is the symbol for Hertz, the unit of frequency: 20 Hz is 20 vibrations a second and 20,000 Hz is 20,000 vibrations per second.

The eighty-eight keys on a standard piano cover just over seven octaves, from A0 to C8 (using scientific pitch notation). A0 is at 27.5 Hz and C8 is 4186 Hz. Middle C (C4) is 261.63 Hz. Doubling the Hertz goes up an octave; halving it goes down one.

Carbon dioxide and PPM

Carbon dioxide (CO₂) is present in the atmosphere in minuscule quantities, so small that its concentration is measured in parts per million (ppm). Because it is a powerful greenhouse gas even little changes have a major effect on the climate. Here are some key CO₂ numbers:

Before the Industrial Revolution: about 280 ppm
Where many people think we need to go down to: 350 ppm
Where we are now (with over +1 ℃ global mean temperature rise): about 400 ppm
RCP2.5, a scenario where emissions peak very soon and then decline: 490 ppm in 2100 (and about +1.5 ℃ increase)
RCP8.5, a scenario where emissions continue to rise: 1370 ppm in 2100 (and about +5 ℃ increase)

(See The Beginner’s Guide to Representative Concentration Pathways and the RCP Database for more about RCPs. They actually use CO₂ equivalent measurements to include other greenhouse gases, but the CO₂ number would be quite close.)

Turning PPM into sound

CO₂ is measured in parts per million, but if we change the units to Hertz then the resulting sounds are in the middle of our hearing range: 280 Hz to 1370 Hz. 280 Hz is just above C# above middle C; 400 Hz is three white keys up; 1370 is one and a half octaves above that.

The table below gives numbers, the nearest pitches and a snippet of the microtonal sound (played in Sonic Pi with the Hoover synth).

PPM	Hz	Near to
280	280	C#4–D4
350	350	F4
400	400	G4–G#4
490	490	B4
1370	1370	F6

The next track is what the Keeling Curve sounds like: it is the monthly interpolated means at Mauna Loa from January 1959 to June 2016 (about 315 to 405 ppm) played with the same method. There are four beats a second, one month per beat, so a year takes three seconds to play. There is a kick drum each January.

But that is fast. GHG.EARTH is slow.

Data

The data comes from Recent Daily Average Mauna Loa CO₂, the official page maintained by the researchers.

There is no machine-readable data feed provided by the NOAA (yet), so I wrote noa₂co₂ to scrape the site and generate a CSV file of all recent data and a JSON file of just the most recent known reading. The readings are generally updated about around 9 AM ET, and usually the previous day’s reading is added, but sometimes it is not available, and in such cases it’s marked NA in the CSV and skipped in the JSON file.