Ahhh. Now they can have it both ways. High CO2 levels cause both global warming and ice ages.
New study shows that the climate cooled and glaciations occurred during the Ordovician period 450 million years ago when the carbon dioxide level in Earth’s atmosphere was approximately 800 percent higher than it is today.
Falling temperatures during times of high carbon dioxide
When non-vascular plants, such as mosses, hornworts and liverwort, attached to rocks such as granite, they began a chemical weathering process that drew down carbon dioxide levels in the atmosphere. Streams and rivers eventually transported the CO2 to the oceans where it was buried as carbonate rock.
See entire article in Nature Communications.
“Weathering of rocks by mosses may explain climate effects during the Late Ordovician”
Thanks to Climate Change Weekly for this link