re: CO2 feedback mechanisms
There are other things, too. Thawing permafrost can generate greenhouse gases. Deep ocean methane ices can be released by warming waters, and is rapidly broken down to water and CO2 in the atmosphere. One wonders how much of the ancient CO2 developing as the Earth warms is left over from methane melts.
Again, it's easy to imagine mechanisms that raise CO2 to high levels in natural cycles. It's not so easy to figure out why they come just as rapidly back down unless the temperature is the driving element.