New paper studies Ordovician Ice Age, which occurred when CO2 was 11 times higher than the present

A paper published today in Palaeogeography, Palaeoclimatology, Palaeoecology studies the timing of the onset of the late Ordovician ice age, which occurred when CO2 levels were more than 11 times higher than the present. The late Ordovician ice age occurred around 450 million years ago, when temperatures plunged 10C from "greenhouse conditions" despite CO2 levels of around 4500 ppm in comparison to today's level of 400 ppm, demonstrating that CO2 is not the "control knob" of climate. 

The late Ordovician ice age occurred around 450 million years ago, when temperatures plunged 10C despite CO2 levels remaining over 11 times higher than the present. 

In fact, the entire geological record demonstrates a disconnect between temperature and CO2 levels, but excellent agreement with the change in cosmic rays, which is a proxy of solar activity. 

Another paper showing the disconnect between calculated temperature due to changes in cosmic rays and CO2 on geologic timescales [the past 500 million years] Source

Oxygen isotopes from Conodont Apatite of the midcontinent, us: implications for late ordovician climate evolution

• Page C. Quinton^, , 
• Kenneth G. MacLeod

•

The δ ¹⁸O_VSMOW values of Katian conodonts fluctuate around 18.9‰.

•

There is no evidence of cooling or glaciation during the sampled ~ 5.7 m.y..

•

Temperatures remained relatively constant throughout most of the Katian.

•

Glaciation began either prior to the Katian or during the Hirnantian.

•

Statistically significant offset exits in δ ¹⁸O for the conodont taxa analyzed.

---

Abstract

The major glaciation at the end of the Ordovician is associated with the 2nd largest mass extinction event of the Phanerozoic. Growth of Late Ordovician ice sheets requires a dramatic cooling from the ‘greenhouse’ conditions that prevailed for most of the Ordovician, but when and how fast this cooling occurred is controversial. The controversy is due in large part to a lack of good geochemical constraints on the temperature history of the Katian (453–445.2 Ma). To address this uncertainty, we measured phosphate δ¹⁸O values from 3 conodont species collected from sections in the midcontinent region of the United States that span an ~ 5.7 m.y. long interval covering most of the Katian. Results reveal a statistically significant offset in δ¹⁸O values between some taxa and show up to 2‰ differences among samples. However, there are no apparent long-term trends within or between sections; rather, values fluctuate around a δ ¹⁸O mean of ~ 19‰ VSMOW. Our study provides the longest, relatively high resolution, species specific conodont record generated for this interval, and we found no evidence supporting progressive cooling during the Katian.