Storyboard: What is permafrost?

What is permafrost?

• Permafrost is ground that stays frozen for at least two consecutive years, covering nearly a quarter of the Northern Hemisphere.
• As Arctic temperatures rise rapidly, this frozen ground begins to thaw, causing the land to subside, damaging roads and buildings, and releasing ancient carbon stores in the form of greenhouse gases.
• The thaw of permafrost is both a local hazard and a global climate concern.
• Understanding where and how permafrost thaws helps us assess future impacts.

Modeling permafrost thaw and subsidence

To model perfafrost thaw, we simulate how ground ice respond to warming. The Community Terrestrial Systems Model with the Excess Ice module (CTSM-EXICE) represents ice-rich soil layers and how melting leads to ground subsidence (right).

Our goal is to quantify land surface subsidence and the potential risks of permafrost thawing in the Arctic region.

The figure on the left illustrates the physical process: in ice-rich permafrost, thawing causes ground collapse, while in low-ice soils, thawing only deepens the active layer.

Warming at the surface

Simulations driven by CNRM show warmer conditions than those driven by NORESM. The 2 m temperature increase is visible everywhere in the Arctic, and warming is more pronounced in the autumn and winter seasons.

Warming at 1m soil depth

The increase in soil temperature at 1 m depth is more moderate than the surface warming but still contributes to long-term permafrost degradation.

Rainfall increase

A more pronounced increase in rainfall is also related to the CNRM-driven runs, and patterns are very similar to T2. Spring, summer and autumn are expected to have the strongest rainfall increase.

Snowfall decline

Interannual variability in snowfall patterns is high. Snowfall decline is faster in CNRM-driven runs. There are regional differences in snowfall patterns, and a strong decline is associated with coastal Norway, among others. Spring and summer are the seasons of the most pronounced snowfall decline throughout the period.

Permafrost extent in 2015

This figure shows the simulated extent of near-surface permafrost in the year 2015 (blue areas), based on four different combinations of two global climate models (GCMs) and two regional climate models (RCMs) that selected from storyline method.

It serves as the baseline for assessing future permafrost degradation. While models differ slightly, they all capture widespread permafrost across Siberia, northern Canada, Alaska, and parts of the Arctic coastline.

Permafrost extent in 2099

By 2099, all model configurations project a significant reduction in permafrost extent compared to 2015.

The remaining permafrost areas (shown in blue) are mostly limited to the high Arctic and isolated cold regions.

Despite differences in climate model configurations, the projected spatial patterns of permafrost loss are highly consistent. This indicates a robust and widespread signal of warming-induced thaw across the Arctic.

Arctic-wide permafrost area projections

• Simulations driven by CNRM show a stronger decrease in permafrost extent than those driven by NORESM.
• This analysis considers two different definitions of permafrost area extent to assess model uncertainty (left figure).
• The right figure, adapted from Steinert et al. (2023), shows global permafrost change (including regions outside the Arctic) based on ten different permafrost extent definitions applied to CMIP6 model outputs.

Change in permafrost area (2015 – 2099)

Despite using two different definitions of permafrost extent, the projected changes between 2015 and 2099 are highly consistent.

This suggests that the overall signal of permafrost loss is robust, regardless of the specific definition applied.

Where will the ground subside the most?

• The largest projected ground subsidence occurs between 60° and 70° N
• five regions within this latitude band (each with equal spatial extent) are selected for detailed analysis, as they are projected to experience more than 1 m of ground subsidence by 2100.

When and Where will subsidence intensify?

The timing of stronger subsidence varies by region, with a general acceleration from 2050 to 2060.

• Regiona 5(Canada) shows the largest average subsidence, about 25 cm, across the models.
• Regiona 4(Alaska-Bering Sea) has the highest uncertainty in subsidence projections.

Model comparision and regional differences

In most regions, permafrost projections from global climate models (GCMs) are more consistent than those from regional climate models (RCMs).

• CNRM-HCLIM-CTSM shows the fastest permafrost thaw across the regions.
• The greatest loss in permafrost area is projected in Region 2, around the Lena river in Russia.