I offer my explanation for why Earth Temperature became more bounded and why the bounding became much tighter in modern time, in the most recent ten thousand years. For most of the last half billion years, the upper temperature bound was set when trying to evaporate all the oceans. You just cannot do that with earth in this orbit location and our current energy balance. Water Vapor is abundant and it radiates with some value times the temperature to the fourth power. The lower bound was set when trying to freeze all the oceans. You just cannot do that with earth in this orbit location and our current energy balance. This temperature, for six hundred million years, was bound in a ten degree range.
During the past fifty million years, Polar Ice developed and the increased albedo lowered the upper temperature bound. Earth uses water, in all of its states, to bound Earth Temperature.
You can see that CO2 is not connected to Temperature. The continents moved and the ocean currents changed and put warm water in the Arctic and around the Antarctic and that caused snowfall. Warm water in the south polar region causes snow to fall in the southern hemisphere and warm water in the north polar region causes snow to fall in the northern hemisphere. The same ocean water circulates through the tropics and the polar regions.
Earth did not have significant polar ice on land until after the warm waters got to the polar regions.