Lenz's law states that the emf's direction is such that its effects oppose the change producing it. 

We may consider the change producing the emf in the ring to be the change in flux linking the ring. This means the flux passing through a surface bounded by the ring. So if you consider a flat surface whose edges are the ring, it's clear that only the downward portions of your green lines matter, because it's these that pass through the surface. 

You would be right to be concerned that there are many surfaces we can draw that are bounded by the ring; some of them would be like bubbles about to detach themselves from a child's bubble-blowing ring. But these surfaces will be cut by green lines going in an opposite direction to the blue lines! Try sketching it! [It's a very neat consequence of the Maxwell equation $\text{Div}\vec{B}=0\ $ that the exact surface doesn't matter in cases like this, provided that it's bounded by the circuit in question.]

Lenz's law gives an unambiguous prediction.