The calculation in Problem #3 was redone much later using the polar pathway extension to the UB/UC model (Kasting et al., 2019). Rather than imbuing the polar pathway with water-like diffusivities, What was done instead?
1) The polar pathway was given diffusivities similar to those of air
2) The polar pathway was given diffusivities similar to those of water
3) The polar pathway was removed from the model
4) The polar pathway was given diffusivities similar to those of ice