A climate-driven weather anomaly appears to be fueling an unprecedented surge in bear attacks across northern Japan, according to new research linking atmospheric changes to forest food scarcity and human-wildlife conflict.
In 2025, bears killed more than a dozen people and injured over 200 others—dramatically exceeding the previous record of six fatalities set in 2023. The threat grew so severe last fall that Japan's Self-Defense Forces deployed troops to Akita Prefecture to assist with bear trapping, while the US embassy in Tokyo issued a rare "wildlife alert" warning American citizens.
The crisis centers on Asiatic black bears, which are not normally aggressive toward humans. That makes the recent "bear crisis" particularly extraordinary, according to Hengjun Xiao, an environmental researcher at Keio University who analyzed the phenomenon.
Xiao's research, reported by Vox, identifies a complex climate mechanism: weakening westerly winds are allowing moist Pacific air to flood northern Japan, increasing cloud cover. With less sunlight reaching forest floors, trees fail to produce the nuts, shoots, and other foods bears rely on before hibernation.
The finding connects climate change to unexpected impacts in developed nations. While much climate research focuses on extreme weather events or sea level rise, this demonstrates how subtle atmospheric shifts can cascade through ecosystems to create dangerous human-wildlife interactions.
By analyzing climate and satellite data, Xiao found that climate change is weakening the westerlies—high-altitude winds that normally bring dry air into Japan and prevent moist Pacific air from penetrating inland. The increased cloudiness reduces photosynthesis in northern forests, diminishing the acorn and beech nut production that bears depend on for pre-hibernation fat accumulation.
Hungry bears venture into human settlements seeking food, leading to encounters that turn fatal. The attacks typically occur in rural areas where elderly residents live alone and cannot escape quickly.
