Reduced Bering Sea Ice Connected to Rising Wildfire Risk in Northeast China

Conversely, the northeastern region of China (lying between 120°E–135°E longitude and 40°N–50°N latitude) has witnessed a notable increase in emissions stemming from both natural wildfires and those triggered by human activities over the past ten years. These emissions have predominantly resulted from biomass burning and now contribute to around 60% of the total burned area in the country. It is essential to note that this area boasts some of China’s most extensive and diverse forest coverage, making it a vital and valuable natural ecosystem and resource that is currently facing a substantial threat.

New research, recently featured in Geophysical Research Letters, delves into the origins of these wildfires. It establishes a connection between a reduction in Arctic sea ice extending from the Arctic to the Bering Sea in the northern Pacific Ocean (ranging from 160°E to 158°W longitude and 53°N to 66°N latitude) and the heightened occurrence of fires during the boreal spring months of March, April, and May.

Researchers, including Guanyu Liu and a team from Peking University, China, combined climate model simulations with actual observational data to explore the connection between these phenomena. Their goal was to uncover how the relationship between declining Bering Sea ice and increased wildfire risk becomes more pronounced with ongoing global warming. To do this, the research team analyzed meteorological data spanning the past four decades to discern shifts in weather conditions conducive to wildfire incidents. Additionally, they examined data related to smoke concentrations and fire radiative power to gain further insights into the situation.

Through modeling, the researchers detected a delay of approximately one month between the disturbance in Bering Sea ice and the onset of wildfires. They propose that this delay might be influenced by ice albedo feedback mechanisms. This feedback mechanism comes into play when solar radiation from the sun is either reflected by the “White” ice or absorbed by the adjacent, relatively “dark” seawater. In the latter scenario, this absorption leads to a warming effect in the surrounding environment, ultimately contributing to the further melting of sea ice and the continued absorption of solar energy. This creates a feedback loop that perpetuates the ongoing decline of sea ice.

When the temperature contrast between the Arctic and lower latitudes diminishes, it leads to a weakening of both the polar and subtropical jet streams. This, in turn, results in a reduction of wind shear, which refers to the change in horizontal wind characteristics with altitude. As a consequence, vertical atmospheric convection above northeast China becomes less prevalent, diminishing the likelihood of cloud formation and, subsequently, the prospects for precipitation.

In their computational experiments, Liu and the research team observed that the reduction in sea ice during the winter season resulted in reduced rainfall and elevated temperatures in northeast China. These changes were influenced by atypical, higher-speed northwesterly wind patterns and the development of high-pressure systems characterized by descending airflow. Consequently, these conditions were identified as a potential ignition source, creating a volatile combination of hot and dry circumstances that could readily trigger and facilitate the rapid spread of wildfires, propelled by strong wind patterns.

These circumstances are made more severe by large-scale climate patterns that extend globally, like the El Niño Southern Oscillation and the Pacific Decadal Oscillation. These phenomena are shaped by the interplay between the atmosphere and ocean, which is influenced by sea surface temperatures in the Pacific Ocean. During their warm, positive phases, both of these climate oscillations tend to promote drought conditions, thus increasing the likelihood of wildfires.

When applying this knowledge to future predictions, especially under the most extreme climate scenario known as Shared Socioeconomic Pathway 8.5 (SSP585), where radiative forcing is projected to increase by 8.5W/m² by the year 2100, the research team discerned a clear and consistent trend of ongoing Bering Sea ice decline and an increased frequency of wildfires in northeast China. Even under the lower radiative forcing scenario of 7W/m² (SSP370), the occurrence of wildfires remained elevated compared to historical records, albeit with a less pronounced pattern. However, for the lowest radiative forcings of 2.67W/m² (SSP126) and 4.57W/m² (SSP245), the relationship between Bering Sea ice decline and wildfires became less apparent.

Anticipating the complete disappearance of Arctic sea ice concentration during summer months by the 2050s, the growing risk of more frequent and destructive wildfires becomes an urgent concern. This necessitates the immediate implementation of management strategies, regardless of the extent of climate change forcing, to address this pressing issue.

Resources

1. ^NEWSPAPER Bird, H. (2023, October 24). Declining Bering Sea ice linked to increasing wildfire hazard in northeast China. Phys.org. [Phys.org]
2. ^JOURNAL Liu, G., Li, J., Ying, T., Su, H., Huang, X., & Yu, Y. (2023). Increasing fire weather potential over northeast China linked to declining bering sea ice. Geophysical Research Letters, 50(19). [Geophysical Research Letters]