The levels of greenhouse gases (carbon dioxide, water vapor, and methane) are high during hothouse. The atmosphere becomes increasing hot and humid. The oceans warm more slowly. Ocean warming begins long before its pronounced atmospheric expression, as the oceans are a vast heat sink.
Volcanic activity can cause short-term variations in climate. Conversely, quick global temperature rises and associated rapid ice melting, as in current times, incites volcanic activity.
Sea level rises as continental glaciers melt. The weight on continents lessens, while the pressure on oceanic tectonic plates increases. This changes the pattern of crust stresses, opening more routes for ascending magma.
This gyre also increases seismic activity. But falling water on land can have its own immediate effect. Heavy rainfall tamps the velocity of seismic waves during earthquakes, slightly lessening their severity.
Icehouse and hothouse are geological time scale trends typically lasting many millions of years. These long-term climatic cycles have had a dramatic effect in shaping the evolution of life, as have shorter climatic cycles when abrupt.