The equable climate problem reminds me of the exoplanetary curiosity of the tidally locked planet. For a long time, people expected that all such planets would

The equable climate problem reminds me of the exoplanetary curiosity of the tidally locked planet. For a long time, people expected that all such planets would have an atmosphere that inevitably crashed out as ice on the cold side, rendering them uninhabitable. More recent computer models of convection suggest that many such worlds would have sufficient convective activity, cycling between altitudes from one side of the planet to the other, to maintain gasses and liquids on the surface. To match the observations, a model simply requires something about higher CO2 levels which specifically encourage hygrothermal exchange between poles and equator, and/or significantly insulates the poles against radiative losses in disproportionate ways versus today. CO2 itself doesn't seem likely to cause this because it's in the gaseous phase for almost all of Earth's history, but substantially increased water in the atmosphere would be the first suspect because water is such a strong thermal reflector when a cold liquid, and not so much when a gas.