Atmospheric and wildfire responses to soil moisture reduction in the idealized experiments using the CESM2. The values represent differences between the response of a 40% soil moisture reduction perturbation experiment in July 2045 and a control simulation: (a) soil moisture in 0–10 cm depth (units: kg/m2), (b) surface air temperature (units: °C), (c) relative humidity at 2 m (units: %), and (d) logarithm of burned area [log (burned area)] (units: km2). Time evolution over Western Siberia (65.5°N, 83.75°E): (e) soil moisture over 0–10 cm depth (units: kg/m2), (f) surface air temperature (units: °C), (g) relative humidity at 2 m (units: %), and (h) logarithm of the burned area [log (burned area)] (units: km2) (blue: control simulation, yellow: 20% soil moisture reduction perturbation experiment, and brown: 40% soil moisture reduction perturbation experiment). Graphic: Kim et al., 2024 / Nature Communications
Atmospheric and wildfire responses to soil moisture reduction in the idealized experiments using the CESM2. The values represent differences between the response of a 40% soil moisture reduction perturbation experiment in July 2045 and a control simulation: (a) soil moisture in 0–10 cm depth (units: kg/m2), (b) surface air temperature (units: °C), (c) relative humidity at 2 m (units: %), and (d) logarithm of burned area [log (burned area)] (units: km2). Time evolution over Western Siberia (65.5°N, 83.75°E): (e) soil moisture over 0–10 cm depth (units: kg/m2), (f) surface air temperature (units: °C), (g) relative humidity at 2 m (units: %), and (h) logarithm of the burned area [log (burned area)] (units: km2) (blue: control simulation, yellow: 20% soil moisture reduction perturbation experiment, and brown: 40% soil moisture reduction perturbation experiment). Graphic: Kim et al., 2024 / Nature Communications

25 September 2024 (IBS Center for Climate Physics) – A study, published in the journal Nature Communications by an international team of climate scientists and permafrost experts shows that, according to new climate computer model simulations, global warming will accelerate permafrost thawing and as a result lead to an abrupt intensification of wildfires in the Subarctic and Arctic regions of northern Canada and Siberia.

Recent observational trends suggest that warm and unusually dry conditions have already intensified wildfires in the Arctic region. To understand and simulate how future anthropogenic warming will affect wildfire occurrences, it is important to consider the role of accelerated permafrost thawing, because it strongly controls the water content of the soil – a key factor in wildfire burning. Recent climate models did not fully consider the interaction between global warming, northern high latitude permafrost thawing, soil water and fires.

Our key finding is that the rapid permafrost thaw results in an abrupt reduction in soil moisture, an increase in surface air temperature and a decline in relative humidity across the Arctic-subarctic region. These climate conditions lead to rapid intensification of wildfires in western Siberia and Canada in the mid-to-end of the 21st century.

Dr. In-Won Kim, lead author of the study and postdoctoral researcher at the IBS Center for Climate Physics in Busan, South Korea, to Newsweek

The new study uses permafrost and wildfire data generated by one of the most comprehensive earth system models – the Community Earth System Model. It is the first model of its kind, which captures the coupling between soil water, permafrost and wildfires in an integrated way. To better separate the anthropogenic effect of increasing greenhouse gas emissions from naturally occurring variations in climate, the scientists used an ensemble of 50 past-to-future simulations covering the period from 1850-2100 CE (SSP3-7.0 greenhouse gas emission scenario), which was recently conducted by scientists from the IBS Center for Climate Physics, Busan (South Korea) and the National Center for Atmospheric Research in Boulder, Colorado (United States) on the IBS supercomputer Aleph.

24 September 2024: This video presents an analysis of the changes in permafrost thaw and wildfires in the Arctic-Subarctic regions in the period of 1850-2100. The lower left color bar represents permafrost areas (white indicates lower active layer thickness and grey indicates higher active layer thickness). The lower right color bar indicates the extent of burnt area, with light colors indicating less burnt area and dark colors indicating more burnt area. The video illustrates that following permafrost thaw, wildfire increases abruptly in western Siberia and Canada in the mid to late 21st century. Video: IBS Center for Climate Physics / Dr. In-Won Kim

With this ensemble modelling approach, the team demonstrated that by the mid to late 21st century anthropogenic permafrost thawing in the Subarctic and Arctic regions will be quite extensive. In many areas, the excess soil water can drain quickly, which leads to a sudden drop in soil moisture, subsequent surface warming and atmospheric drying (Figure 1). “These conditions will intensify wildfires,” says Dr. In-Won Kim, lead author of the study and postdoctoral researcher at the IBS Center for Climate Physics in Busan, South Korea. “In the second half of this century, our model simulations show an abrupt switch from virtually no fires to very intensive fires within just a few years” she adds.

These future trends will be further exacerbated by the fact that vegetation biomass is likely to increase in high latitude areas due to increasing atmospheric CO2 concentrations. This so-called CO2 fertilization effect therefore provides extra fire fuel.

Maps showing abrupt changes over the historical permafrost regions. The timing of abrupt changes in (a) maximum annual active layer thickness (ALT), (c) soil ice content, and (e) soil moisture in 0–10 cm depth, which is defined by a median year among abrupt changes from the 50 ensemble members (units: year). The abrupt changes of (b) ALT (units: m), (d) soil ice content (units: kg/m2), and (f) soil moisture in 0–10 cm depth (units: kg/m2), which is defined by differences during 20 years of pre- and post- abruptness. Blue (or yellow) star markers in panels a–f indicate a representative grid box in western Siberia (65.5°N, 83.75°E). Time evolution of (g) soil temperature in 0–10 cm depth (units: °C) (blue), (h) ALT (units: m) (purple) for an exemplary grid point in the representative grid box (65.5°N, 83.75°E), (i) soil ice content (units: kg/m2) (red), and (j) soil moisture in 0–10 cm depth (units: kg/m2) (green) in 50 ensemble members. Bold lines indicate ensemble means and thin lines indicate individual ensemble members in panels g–j. Here we focus on near-surface permafrost processes. We therefore define the historical permafrost regions as the area where ALT is less than 3 m for the period of 1850–186954,55,56. Graphic: Kim et al., 2024 / Nature Communications
Maps showing abrupt changes over the historical permafrost regions. The timing of abrupt changes in (a) maximum annual active layer thickness (ALT), (c) soil ice content, and (e) soil moisture in 0–10 cm depth, which is defined by a median year among abrupt changes from the 50 ensemble members (units: year). The abrupt changes of (b) ALT (units: m), (d) soil ice content (units: kg/m2), and (f) soil moisture in 0–10 cm depth (units: kg/m2), which is defined by differences during 20 years of pre- and post- abruptness. Blue (or yellow) star markers in panels a–f indicate a representative grid box in western Siberia (65.5°N, 83.75°E). Time evolution of (g) soil temperature in 0–10 cm depth (units: °C) (blue), (h) ALT (units: m) (purple) for an exemplary grid point in the representative grid box (65.5°N, 83.75°E), (i) soil ice content (units: kg/m2) (red), and (j) soil moisture in 0–10 cm depth (units: kg/m2) (green) in 50 ensemble members. Bold lines indicate ensemble means and thin lines indicate individual ensemble members in panels g–j. Here we focus on near-surface permafrost processes. We therefore define the historical permafrost regions as the area where ALT is less than 3 m for the period of 1850–186954,55,56. Graphic: Kim et al., 2024 / Nature Communications

“To better simulate the future degradation of the complex permafrost landscape, it is necessary to further improve small-scale hydrological processes in earth system models using extended observational datasets,” says Associate Prof. Hanna Lee, co-author of the study at the Norwegian University of Science and Technology, in Trondheim, Norway.

“Wildfires release carbon dioxide, and black and organic carbon into the atmosphere, which can affect climate and feed back to the permafrost thawing processes in the Arctic. However, interactions between fire emissions and the atmospheric processes have not been fully integrated into earth system computer models yet. Further consideration of this aspect would be the next step,” says Prof. Axel Timmermann, co-author of the study and director of the ICCP and Distinguished Professor at Pusan National University.

Contact

  • For further information or to request media assistance, please contact: U-Jeong Seo, IBS Center for Climate Physics, Pusan National University (+82-51-510-7328, u_jeongs@pusan.ac.kr)

Abrupt intensification of northern wildfires due to future permafrost thawing

Permafrost thaw occurs in response to increasing greenhouse gas concentrations when soil temperatures exceed 0 °C. A rapid thaw over the ice-rich Arctic-Subarctic permafrost regions can trigger a subsequent abrupt drying of the upper soil due to increasing soil water percolation and an associated reduction in summer soil evaporation. This, in turn, increases sensible heat fluxes from the surface to the atmosphere, generating near-surface atmospheric warming and an increase in atmospheric dryness. These rapidly emerging conditions can promote wildfire. Moreover, positive trends in CO2 fertilization in the CESM2-LE model further increase vegetation carbon stocks, which can serve as additional fuel for combustion, thereby contributing to the intensification of wildfires. Graphic: Kim et al., 2024 / Nature Communications
Permafrost thaw occurs in response to increasing greenhouse gas concentrations when soil temperatures exceed 0 °C. A rapid thaw over the ice-rich Arctic-Subarctic permafrost regions can trigger a subsequent abrupt drying of the upper soil due to increasing soil water percolation and an associated reduction in summer soil evaporation. This, in turn, increases sensible heat fluxes from the surface to the atmosphere, generating near-surface atmospheric warming and an increase in atmospheric dryness. These rapidly emerging conditions can promote wildfire. Moreover, positive trends in CO2 fertilization in the CESM2-LE model further increase vegetation carbon stocks, which can serve as additional fuel for combustion, thereby contributing to the intensification of wildfires. Graphic: Kim et al., 2024 / Nature Communications

Abrupt increase in Arctic-Subarctic wildfires caused by future permafrost thaw

ABSTRACT: Unabated 21st-century climate change will accelerate Arctic-Subarctic permafrost thaw which can intensify microbial degradation of carbon-rich soils, methane emissions, and global warming. The impact of permafrost thaw on future Arctic-Subarctic wildfires and the associated release of greenhouse gases and aerosols is less well understood. Here we present a comprehensive analysis of the effect of future permafrost thaw on land surface processes in the Arctic-Subarctic region using the CESM2 large ensemble forced by the SSP3-7.0 greenhouse gas emission scenario. Analyzing 50 greenhouse warming simulations, which capture the coupling between permafrost, hydrology, and atmosphere, we find that projected rapid permafrost thaw leads to massive soil drying, surface warming, and reduction of relative humidity over the Arctic-Subarctic region. These combined processes lead to nonlinear late-21st-century regime shifts in the coupled soil-hydrology system and rapid intensification of wildfires in western Siberia and Canada.

Abrupt increase in Arctic-Subarctic wildfires caused by future permafrost thaw