Eocene
Another method considered for producing the warm polar temperatures were polar stratospheric clouds. Polar stratospheric clouds are clouds that occur in the lower stratosphere at very low temperatures. Polar stratospheric clouds have a great impact on radiative forcing. Due to their minimal albedo properties and their optical thickness, polar stratospheric clouds act similar to a greenhouse gas and traps outgoing longwave radiation. Different types of polar stratospheric clouds occur in the atmosphere: polar stratospheric clouds that are created due to interactions with nitric or sulfuric acid and water (Type I) or polar stratospheric clouds that are created with only water ice (Type II).
Cloud physics
There are two main model schemes that can represent cloud physics, the most common is bulk microphysics models that uses mean values to describe the cloud properties (e.g. rain water content, ice content), the properties can represent only the first order (concentration) or also the second order (mass).
The second option is to use bin microphysics scheme that keep the moments (mass or concentration) in different for different size of particles.
The bulk microphysics models are much faster than the bin models but are less accurate.