Calders and Roe showed how northern hemisphere summer insolation corresponds to the rate of change of ice volume and Huybers showed that deglaciations happened during times of high precession and especially obliquity, but in the late Pleistocene some obliquity cycles are skipped, resulting in 80 and 120 thousand year periods.
|The orbital forcing function is a linear combination of obliquity and climatic precession.|
The red peaks are deglaciations. The overall correlation of the two graphs is 65%.
Lisiecki and Raymo use orbital tuning to constrain the age of the benthic records, while Huybers explicitly avoids this, consequently the two datasets are occasionally completely out of phase, but generally in good agreement, especially in the late Pleistocene.
As fitness function we take the product of the sum of squared errors (SSE) between the model and the two reference records from 2580 thousand years before present, with 1000 year timesteps.
Backcast of the model for the last million years, and reference data.
The early Pleistocene is also used for optimization, but not shown.
|Forecast of the model for the next million years.|
The error bounds should not be taken too seriously, as it's just the statistical error assuming the model is 100% correct, which it is obviously not.
For a better error estimate, one should compare several models:
Download the consolidated data, including orbital parameters, insolation calculations, reference data and model output: