Hmmm… I notice that there doesn't appear to be any way to reflect situational modifiers.
Suggestion: Add or subtract D4s from the basic dice pool.
Say a character is trying to scale a wall. If it's just a standard brick wall, the roll for that might be a pool of (Dexterity) D4s.
But what if it's raining? That would make it harder to climb, so subtract one from the pool—that is, roll (Dexterity - 1) D4s. And if it's really raining, I mean a torrential downpour, the character might need to roll (Dexterity - 2) D4s, or perhaps even worse.
If the wall has a bunch of bricks sticking out which are usable as handholds and footholds, that would make it easier to climb, so go with a pool of (Dexterity + 1) D4s.
And so on, and so forth.
If you choose to make use of this suggestion, you should prolly decide what to do if the pool penalties reduce the pool to zero dice or less. Perhaps the simplest way to go might be to declare the minimum dice pool to be 1D4, end of discussion. There are other alternatives, which are somewhat more complex.