ISIS on the offensive in Iraq

[Viking]

Depends on the scope. I would say airpower can make it hard for ISIS to move around in the open but it cannot aid inner city fights as well.
Making them unable to move around gives the other powers more time to recover and build up and makes it harder for ISIS to operate.
In Libya there was most certainly an effect from bombing Gadaffi's army.

Whether it spells the total defeat of ISIS is probably less sure if that is what you mean.

I mean, this intervention can prove decisive in the sense that it can establish areas where ISIS can conquer land and where they can not (although ISIS being allowed to take shia-dominated areas as well as Kurdish areas seemed to be out of the question since the beginning of this, anyway).

But the limited scope of the intervention means that it is unlikely to have a major impact on the ability of ISIS to hold most of the areas they have already conquered.