  We present evidence that two dimensional Dirac fermions in the presence of
random Abelian gauge potential exhibit a phase transition when the disorder
strength exceeds a certain critical value. We argue that this phase transition
has novel properties unique to disordered systems. It resembles in many ways
the transition from dilute to dense polymers phase in two dimension. In
particular, we argue that the central charge of the disordered Dirac fermions,
being $c=0$ before the transition, changes to $c=-2$. We discuss possible
implications to quantum Hall transitions, in view of recently proposed model
for quantum Hall transitions with $c=-2$.
