What are the optimal climate policies when time preferences deviate from the standard exponential discounting and decision makers cannot commit to future policies? We show that, with time-declining discounting, the delay and persistence of climate impacts provide a commitment device to policy makers. We quantify the commitment value in a climate-economy model by solving time-consistent Markov equilibrium capital and emission taxes explicitly. The returns on capital and climate investments are no longer equal, leading to a large increase in the emission tax, compared to a benchmark with equalized returns. The commitment value increases the tax by a factor of 20 in our quantitative assessment.