[ChessExpert]

"If it gets cold, ice caps form, chemical weathering decreases, carbon dioxide accumulates in the atmosphere,

Slowly now: chemical weathering decreases, carbon dioxide accumulates in the atmosphere,

How does a decrease in weathering lead to an increase in CO2?

If it gets hot, the rate of chemical weathering increases, the rate of burial of sedimentary carbonates increases, the amount of carbon dioxide in the atmosphere ... decreases

Carbonate = CO3, if I’m not mistaken. So the argument is that CO3 gets buried as a result of weathering. Where does the CO3 come from? How is it buried?

I don’t follow this argument well enough to explain to anyone else.

[NicknamedBob]

"...chemical weathering decreases, carbon dioxide accumulates in the atmosphere, ..."

How does a decrease in weathering lead to an increase in CO2?

As near as I can piece it together, chemical weathering in this instance is primarily the action of carbon dioxide dissolved in rainwater, making carbonic acid. With lower temperatures and much water locked up as ice, there would be less rainfall.

Less rain to dissolve the carbon dioxide out of the atmosphere, thus letting it accumulate.

It may be that CO₂ levels act as a control only at the lower temperature levels, while H₂O functions as the high-temperature safety valve. -- CO₂ accumulation keeps the world from staying frozen, and the boiling convention action and reflection characteristics of water vapor accumulation keeps it from getting too hot.