The Ordovician glaciation was a brief excursion to coldness during an otherwise warm era, due to a coincidence of conditions. It is completely consistent with climate science.
CO2 was higher in the past
“The killer proof that CO2 does not drive climate is to be found during the Ordovician- Silurian and the Jurassic-Cretaceous periods when CO2 levels were greater than 4000 ppmv (parts per million by volume) and about 2000 ppmv respectively. If the IPCC theory is correct there should have been runaway greenhouse induced global warming during these periods but instead there was glaciation.”
(The Lavoisier Group)
Geologists refer to ancient ice-cap formations and ice-ages as “glaciations.” One such glaciation that occurred during the Late Ordovician era, some 444 million years ago has captured the attention of climate scientists and skeptics alike. To get some perspective on timing, that’s just over 200 million years before
— source skepticalscience.com | 6 Jul 2015