First Quantification of the Permafrost Heat Sink in the Earth's Climate System

Abstract

Due to an imbalance between incoming and outgoing radiation at the top of the atmosphere, excess heat has accumulated 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 used to melt ground ice in permafrost. Here, we diagnose changes in sensible and latent ground heat contents in the northern terrestrial permafrost region from ensemble‐simulations of a tailored land surface model. We find that between 1980 and 2018, about 3.90+1.4−1.6 $3.9\genfrac{}{}{0pt}{}{+1.4}{-1.6}$ ZJ of heat, of which 1.70+1.3−1.4 $1.7\genfrac{}{}{0pt}{}{+1.3}{-1.4}$ ZJ (44%) were used to melt ground ice, were absorbed by permafrost. Our estimate, which does not yet account for the potentially increased heat uptake due to thermokarst processes in ice‐rich terrain, suggests that permafrost is a persistent heat sink comparable in magnitude to other components of the cryosphere and must be explicitly considered when assessing Earth's energy imbalance.

Academician Guodong Cheng's Contributions to Permafrost Science

“…Approximately 99% of global permafrost is distributed in the Northern Hemisphere [3,4], accounting for 21% of the total Northern Hemisphere land area [5]. Large quantities of ice and organic carbon are stored in permafrost [6,7], which features unique hydrothermal and mechanical properties [8,9]. Permafrost change is closely related to human well-being, as it regulates the water cycle and climate and affects engineering substrate stability.…”

Robust Reconstruction of Historical Climate Change From Permafrost Boreholes

“…The second panel (b) shows total latent heat change as estimated by Nitzbon et al. (2023) for the time period 1980–2018. Higher latent heat change generally indicates more thaw.…”

“…The model outputs from Nitzbon et al. (2023) and Langer et al. (2024) used in Figure 1 are also available on Zenodo (Langer et al., 2022b).…”

“…The historical air temperature forcing data used in the synthetic experiments can be downloaded from Zenodo (Langer et al, 2022a). The model outputs from Nitzbon et al (2023) and Langer et al (2024) used in Figure 1 are also available on Zenodo (Langer et al, 2022b). Air temperature data from Tiksi can be obtained directly from the NOAA Climate Data Center (NOAA National Centers of Environmental Information, 1999).…”

“…Consequently, such reconstructions necessarily assume that the depth of the permafrost table does not change over the full reconstruction period since the spatial domain of the model is typically treated as constant. Second, in regions with warmer permafrost, here defined as those with mean annual ground temperatures (MAGT) ≥−5°C (Nitzbon et al., 2023), and finer grained soils with moderate to high silt or clay content, latent heat effects may be present even well below the top of the permafrost (Nicolsky & Romanovsky, 2018; Romanovsky & Osterkamp, 2000). This is due to the persistence of unfrozen water in soil pores at subzero temperatures as a result of capillary action (Koopmans & Miller, 1966).…”