Concerning my planet, I decided to go with the hothouse climate. It's interesting...
- global circulation stays the same: rising air at the equator, falling air at the tropics, rising air at the polar circles and falling air at the poles as well as corresponding humid and arid belts*.
- temperature gradient between the equator and the poles is small: this is especially true of the sea, but also of land**. Absolute global temperatures are higher, but high latitudes are relatively much warmer and low latitudes may be relatively colder. There's still tropical and temperate rainforests separated by an arid zone, but the flora and fauna of temperate rainforests ends up being pretty much the same as that of tropical rainforests. Poles may be warm enough to support broadleaf forests and there is no permanent ice and snow at the poles.
- increased temperature, especially ocean temperatures, means increased evaporation and increased precipitation. Humid belts expand and arid belts contract: instead of 10 degrees, tropical rainforests extend to 20 degrees north an south, tropical grasslands partially or, if the continent is small and maritime enough, completely replace tropical deserts, which are in any case limited to the immediate neighborhood of horse latitudes. Poles end up being much wetter (I haven't read this everywhere, but I suspect they're dry today because it's so cold there's practically no evaporation). The resulting cloud cover is thought to prevent them from loosing too much heat during winter.
It's interesting to thing how civilization might develop in this world. Would the polar latitudes be a good place to develop agriculture? They'd be habitable but there'd still be a need to store food for winter since I doubt leaves or fruits would grow during a months long night. As for urbanized, large-scale civilizations, it is thought they developed where there was a need for irrigation, and there'd be much less such areas in a hothouse world than in an icehouse one.
*Uninhabitable tropics in the Triassic and the early Jurassic seem to be a result of contemporary geography, namely the existence of Pangea: arid belts expanded towards the equator and deserts replaced the rainforest, likely because of increased continentality and monsoons so that evaporation around the equator exceeded precipitation. This was somewhat like Somalian climate, but on a larger scale: central and eastern tropical Pangea was completely arid while western tropical pangea was more hospitable. None of that applies to my planet.
**Some pollen finds from Antarctica suggest palm trees and other subtropical vegetation at the coasts, and broadleaf forests akin to those of New Zealand inland. This lends credence to the idea that a circumequatorial current driven heat transport trough the oceans is a key component of hothouse climates.