The role of carbon farming in agriculture or forestry to mitigate climate change is currently under intensive scientific discussion along with the gradual but progressing evolution of the voluntary carbon market and its certification. An overarching issue is the question of the permanence of terrestrial carbon sinks. In this comment, I discuss the climate benefit of non-permanent carbon sinks in light of a recent publication stating that carbon certificates fall short of expectations for climate change mitigation because of their non-permanence. The beneficial effect of short-lived sinks is real and quantifiable, and this understanding is applicable within ex ante biophysical discounting, which has the potential to improve the trustworthiness of climate change mitigation via carbon farming.