Due to an imbalance of incoming and outgoing radiation at the top of the atmosphere, excess heat has been accumulating in Earth’s climate system in recent decades, driving global warming and climatic changes. To date it has not been quantified how much of this excess heat is being used for the melting of ground ice in the terrestrial permafrost region. Here, we diagnose changes in sensible and latent heat contents in the northern terrestrial permafrost region from ensemble simulations of a numerical permafrost model. We find that about 3.9 (+1.5|-1.7) ZJ of heat, of which 1.7 (+1.4|-1.5) ZJ (45%) were used to melt ground ice, were taken up by permafrost from 1980 to 2018. This suggests that permafrost is a persistent heat sink similar in magnitude to other components of the cryosphere that requires an explicit consideration in assessments of the Earth’s energy imbalance.