The discrepancy in measurements of H_0 is the most notable anomaly in contemporary cosmology with significance as large as 6σ. Despite many attempts, there is yet no compelling solution to the H_0 tension. In the first part of my talk, I review the H_0 tension. In particular, I will clarify why it is so diffcult to solve the tension. In the latter part, I will present our model, which is based on modified recombination in a closed Universe. Starting from general discussion on necessary conditions that successful modified recombination models should satisfy to fit CMB observations, I will demonstrate time-varying m_e models indeed satisfy those conditions. To fit low-z distance measurements such as baryon acoustic oscillation and type-Ia supernovae, a positive spatial curvature plays an essential role. Compared to the canonical ΛCDM, our model improves the chi-square by more than 23. We also show our model solves the lensing anomaly in Planck data concurrently.