Recently, BICEP2 measurements of the cosmic microwave background (CMB) B-mode polarization has
indicated the presence of primordial gravitational waves at degree angular scales, inferring the tensor-toscalar
ratio of r = 0.2 and a running scalar spectral index, provided that dust contamination is low. In
this Letter, we show that the existence of the fluctuations of cosmological birefringence can give rise to
CMB B-mode polarization that fits BICEP2 data with r < 0.11 and no running of the scalar spectral index.
When dust contribution is taken into account, we derive an upper limit on the cosmological birefringence,
Aβ2 < 0.0075, where A is the amplitude of birefringence fluctuations that couple to electromagnetism
with a coupling strength β.