An atmospheric pCO2 threshold for glaciation in the Late Ordovician
Level 5 - mechanism / opinion, no new human data
Level 5 by design analogy (computational climate modeling and theoretical simulation, not clinical CEBM)
OpenAlex W2064035523 · doi:10.1130/0091-7613(1997)025<0447:aapctf>2.3.co;2
What was done
A climate model study evaluated the sensitivity of the Late Ordovician climate to changes in atmospheric carbon dioxide (pCO2). Five simulation experiments were performed with a 4.5% reduction in solar luminosity to assess permanent snow cover as an indicator for glacial inception.
What was found
Permanent snow cover varied markedly across the five simulations. An atmospheric CO2 level of 18 times the present atmospheric level (18X PAL) produced an ice-free climate, whereas 8X PAL triggered a "runaway" icehouse state. This sensitivity across the 18X to 8X range, mediated by ice-albedo feedbacks, falls within existing geochemical uncertainty for the period and suggests a brief drawdown via organic carbon burial could trigger the ~1 m.y. glaciation.
Why it matters
This modeling provides a plausible mechanism for how a brief, rapid glaciation could occur during the generally warm, ice-free early Paleozoic without requiring tectonic-timescale drivers.
Limits
The conclusions are derived entirely from computer model simulations rather than direct empirical proxy measurements. The findings are contingent on assumed boundary conditions, simplified feedback representations, and geochemical estimates of Ordovician pCO2 that carry wide uncertainties.
Cited by
- context There have been periods in Earth's history when atmospheric carbon dioxide levels were significantly higher than today while global temperatures were significantly colder.