This piece is part of a collection of sound compositions called Timescales, which sonifies datasets spanning different time scales of the atmospheric carbon record. The Holocene is a geologic epoch which began approximately 11,700 years ago as the last glaciation ended. At the onset of the Holocene, atmospheric carbon dioxide concentrations were approximately 265 ppm, and they remained below 280 ppm until the 18th century and the dawn of the industrial revolution. The Holocene composition creates an experience of listening to the stable climate of the Holocene epoch, and hearing the end of the Holocene and the beginning of the Anthropocene. 

Holocene uses a repeated melody that is three measures long, each measure is a three-tone sequence with scale degrees: [3,1,3], [3,3,5], [3,3,8].  Each measure corresponds to one data point, and the pitch for all notes in the measure are determined by the mapped carbon midi value, so that repeated CO₂ midi values create a repeating melody. When the CO₂ value shifts up or down, the whole measure shifts by the same degree, preserving the interval between notes. This way, the melodic structure stays the same, but is translated up or down the scale according to the carbon record.  The CO₂ value in ppm is mapped to a pentatonic (five-note) equal-temperament scale spanning six octaves, from 392 Hz to 5587.65 Hz (assigned as MIDI values).  This pitch value determines the pitch of the first note in each measure. The other two pitches in the measure are determined in relation to the first pitch, by the aforementioned scale degrees.

The mapping of historical time to musical time is as follows; in the first 70 beats, each beat represents 75 historical years. Then, this shifts to 50 historical years represented per beat for 63 beats, and gradually reduces to 1 historical year per beat. This nonlinear time mapping stretches out the recent rise in CO₂ relative to the stable period. 

To remind listeners that historical time ‘slows down’ as musical time progresses, this piece includes a digital instrument that plays the number of historical years represented per beat. The sound is a simple thud sound made with FM synthesis. For the first three intervals (75, 50, and 25 years per beat), the instrument sounds like buzzing. When the time interval reaches 10 or fewer historical years per beat, each individual thud sound is audible and becomes rhythmic.

Data sonified is from the following two sources:

• Law Dome ice core (Rubino et. al., 2019) for years 1 CE  to present, and Epica ice core (Lüthi et al., 2008) of years 8000 BCE to  1 BCE. Both of these ice cores are from Antarctica, and are significantly correlated with Antarctic temperature.
• Rubino, Mauro; Etheridge, David; Thornton, David; Allison, Colin; Francey, Roger; Langenfelds, Ray; Steele, Paul; Trudinger, Cathy; Spencer, Darren; Curran, Mark; Van Ommen, Tas; Smith, Andrew (2019): Law Dome Ice Core 2000-Year CO2, CH4, N2O and d13C-CO2. v1. CSIRO. Data Collection. https://doi.org/10.25919/5bfe29ff807fb

Data is in a 24-bit, 44100Hz stereo wav file, and can be played through any digital music player.