温暖化が招く集中豪雪と雪不足気ままなリライト189
There is ongoing question about whether every extreme weather event can be directly attributed to man-made global warming. While global warming is undoubtedly a major factor influencing weather patterns, it is crucial to avoid overgeneralizing. Climate systems are highly complex, with other factors—such as natural variability, ocean currents, and local topography—playing significant roles in shaping regional weather. Many scientists support the theory that human-induced climate change, primarily driven by greenhouse gas emissions, is having a widespread influence on weather patterns worldwide. However, some remain skeptical, arguing that the connection between global weather extreme events and human-driven climate change requires further investigation.
Rising global temperatures and their associated impacts have brought about a series of unprecedented weather events, including a seemingly contradictory phenomenon explained by climate science—how "global warming can cause heavy snow". Warmer ocean surface temperatures and shifts in atmospheric circulation are driving weather anomalies, resulting in heavy snowfall in some regions and snow shortages in others. A key factor is that warmer air holds more moisture, increasing the intensity of precipitation. When temperatures remain below freezing, this additional moisture can lead to heavy snowfall, as seen in parts of Japan’s Tohoku region. However, in other areas, rising temperatures disrupt the delicate balance needed for snow formation, leading to snow shortages that pose challenges for winter tourism-dependent regions.
The rise in global average surface temperature over the past 150 years represents an unprecedented shift, standing out sharply against thousands of years of relative climate stability. Temperature reconstructions from ice cores and other sources reveal that natural variability in global temperatures over the last 10,000 years—prior to industrialization—was relatively minor, typically fluctuating within ±0.5°C. By contrast, the current 1.1°C of warming far exceeds this range, more than doubling the bounds of natural variability observed over the past 10 millennia. Moreover, the speed of this warming is remarkable. Today’s warming rate, approximately 1.1°C per century, is 10 times faster than natural warming events, such as the end of the last ice age approximately 12,000 years ago. During that period, global temperatures increased by 4–5°C, but this change occurred gradually over roughly 5,000 years, averaging a rate of just 0.1°C per century.
The current observed global warming of 1.1°C has influenced the background conditions that shape weather events, including snowfall patterns, leading to an increase in the frequency of concentrated heavy snowfall over short periods. Since the 2010s, the number of locations experiencing record-breaking snowfall levels has risen nearly fourfold compared with the 1990s and 2000s. An analysis of maximum one-day snowfall at observation points across the country shows that 19 locations have recorded new all-time snowfall records since 2010, accounting for 20% of all observation sites. By contrast, only three locations set new records in the 1990s, and two in the 2000s. Nationally, the proportion of total annual snowfall occurring on the snowiest day of the year has been steadily increasing. For example, in February 2024, Nagano City experienced a single-day snowfall of 31 cm, which accounted for 26% of its entire annual snowfall in just one day. On a national scale, this proportion has risen by 2–3 percentage points over the last decade, up from the low teens in the 2000s, signaling a rise in the intensity of heavy snow events. Hiroaki Kawase, Senior Researcher at the Meteorological Research Institute, explained, “Heavy snowfalls that were once considered once-in-a-decade events now occur four to five times more frequently in the Hokuriku region.”
While the 1.1°C global warming over the past 150 years has created long-term trends, short-term fluctuations in snowfall are expected to continue due to natural climate variability. In many regions, rising temperatures are leading to shorter snow seasons and a general decrease in total snowfall. However, as the climate changes, the year-to-year variability in snowfall is increasing. Some years may experience extreme snowfall due to the higher moisture content of a warmer atmosphere, while others may see record-low snow accumulation due to elevated temperatures. At five major observation points managed by Niigata Prefecture, the annual maximum snow depth (averaged across these sites) has shown greater variability since around fiscal 2005. For example, the maximum snow depth exceeded 170 cm in fiscal 2020 but dropped below 20 cm the year before. This stark contrast highlights the interplay between warming temperatures and natural variability, resulting in more pronounced fluctuations in snowfall.
The polarization of snowfall patterns has created a double whammy: the devastating toll of extreme snowfall on lives and municipal budgets, and the economic losses caused by warmer winters. When it comes to extreme heavy snowfall events, the decade leading up to 2022 saw 772 fatalities during snow removal operations—three times the number recorded 30 years earlier. At the beginning of 2025, a record-breaking snowfall in Aomori Prefecture tragically claimed seven lives. The economic toll of heavy snowfall has been equally severe. Emergency allocations to cover snow clearing on local roads have placed a significant financial burden on municipalities. During fiscal 2021, which experienced record-breaking snowfall, these allocations reached 55.7 billion yen, the highest amount on record. Similarly, during the 2023–2024 season, heavy snowfall caused vehicles to become stranded on major highways such as the Meishin Expressway, prompting the Ministry of Land, Infrastructure, Transport, and Tourism to issue emergency funds that exceeded initial municipal budgets. On the other end of the spectrum, warmer winters and insufficient snowfall have severely plagued regions reliant on winter tourism. For example, Iwate Prefecture’s beloved "Iwate Snow Festival" was permanently discontinued in 2022 by its organizing committee, following its final event in 2020, due to a lack of sufficient snowfall.