Dynamical dark energy or simply cosmic curvature?

We show that the assumption of a. at universe induces critically large errors in reconstructing the dark energy equation of state at z >= 0.9 even if the true cosmic curvature is very small, O(1%) or less. The spuriously reconstructed omega(z) shows a range of unusual behaviour, including crossing of the phantom divide and mimicking of standard tracking quintessence models. For 1% curvature and Lambda CDM, the error in w grows rapidly above z similar to 0.9 reaching (50%, 100%) by redshifts of (2.5, 2.9) respectively, due to the long cosmological lever arm. Interestingly, the w(z) reconstructed from distance data and Hubble rate measurements have opposite trends due to the asymmetric influence of the curved geodesics. These results show that including curvature as a free parameter is imperative in any future analyses attempting to pin down the dynamics of dark energy, especially at moderate or high redshifts.