やはり温暖化なのか？：2025年2月1日（土）

2025年に入り，1月9日午後から1月10日午前にかけて，京都市北区では雪が1cmほど降ったものの，その後は，結局，京都市で積雪となるまでの降雪は起きなかった。

　温暖化が進むと豪雪災害が起きることが懸念されている。これは，日本海の対流圏下層に位置する高度1kmのところに1,000㎞の長さの風の収束帯（日本海寒帯気団収束帯，Japan-sea Polar airmass Covergence Zone: JPCZ）が停滞し，地球温暖化により海面水温が上昇して，JPCZの停滞が積乱雲を発生させることによって，雪氷災害が起きるといわれているからである。

　しかし，今年の1月31日までは，豪雪どころか，京都市北区上賀茂神社から見える比叡山の姿が，温暖化の進展を如実に示していた。1月だというのに，比叡山の山の斜面が春の山のようだった。今年1月になって，比叡山の山頂付近が雪化粧をしたのは，1月10日の朝だけであった。

　この近辺では，この冬にずっと雪化粧をしている山は，比良山系の蓬莱山（標高1,174ｍ）や権現山（標高996ｍ）などの山々や，伊吹山（標高1,377m）くらいだろうか。そう言えば，京都産業大学に着任して数年後にワンダーフォーゲル部の顧問を大学から命ぜられ，学生たちが比良山系に登山をすると言うので，事前に研究室で学生が作成した「登山計画」をチェックしたことがあった。

　京都は夏は暑く，冬は寒い。そして，その合間の春秋が絶妙な移り変わりを演じるといった，四季折々の美しい景色が名物であったが，温暖化によって何かメリハリのない単調な気候の変化に物足りなさを感じてしまう。

　こうしたなかで，1月27日，気象庁は「早期天候情報」の低温情報を発表し，2月4日から2月10日まで，10年に1度程度しか起きないほどの低温となると予報を出して注意を呼び掛けた。今年の節分は2月2日，2月3日は立春と暦の上では春の到来となるが，今年は季節遅れの「立春寒波」の冬将軍が襲来し，2月が本格的な豪雪時期となりそうだ。京都市北区の2月4日以降の数日間の最低気温が零下4℃と予想されている。近年では珍しく寒くなるようだ。

　日本では，旧暦の月に和風月名と呼ばれる日本独自の月の呼び名を付けてきた。2月は如月（きさらぎ）といい，まだ寒さが残っていて，衣を重ね着する（更に着る）月であることから衣更着（きさらぎ）といわれているそうだ。

Is It Really Global Warming? : Saturday, February 1, 2025

In 2025, snow fell about 1 cm in Kyoto's Kita Ward from the afternoon of January 9 through the morning of January 10. However, after that, there was no snowfall significant enough to result in accumulation in Kyoto City.

As global warming progresses, concerns have been raised about the possibility of heavy snowfall disasters. This is due to the phenomenon where a 1,000-kilometer-long wind convergence zone (known as the Japan-Sea Polar Airmass Convergence Zone, or JPCZ), located at an altitude of about 1 km in the lower troposphere over the Sea of Japan, stagnates. Rising sea surface temperatures caused by global warming are believed to trigger the formation of cumulonimbus clouds in the JPCZ, leading to snow and ice disasters.

However, as of January 31 this year, far from experiencing heavy snowfall, the view of Mount Hiei from Kamigamo Shrine in Kita Ward, Kyoto City, clearly reflected the progression of global warming. Despite it being January, the slopes of Mount Hiei resembled those of a spring mountain. This January, the only time the summit area of Mount Hiei was covered in snow was on the morning of January 10.

In this region, the only mountains that have remained snow-covered this winter are likely those in the Hira mountain range, such as Mount Hōrai (1,174 m) and Mount Gongenyama (996 m), as well as Mount Ibuki (1,377 m). Speaking of which, a few years after I joined Kyoto Sangyo University, the university assigned me as an advisor to the mountaineering club. When the students mentioned their plans to climb the Hira mountain range, I remember reviewing their "climbing plan," which they had prepared in advance, in my office.

Kyoto has long been known for its beautiful seasonal landscapes, with hot summers, cold winters, and the perfect transitions of spring and autumn in between. However, with global warming, the climate has lost much of its dramatic seasonal variation, leaving a somewhat bland and monotonous impression.　

Against this backdrop, on January 27, the Japan Meteorological Agency issued an “Early Weather Advisory” for low temperatures, warning that the period from February 4 to February 10 could bring a cold wave so severe that it occurs only once every ten years.

This year, Setsubun falls on February 2, and February 3 marks the beginning of spring according to the traditional calendar. However, instead of an early spring, an unseasonal “Risshun Cold Wave” is expected to arrive, bringing full-fledged heavy snowfall in February.

In Kyoto’s Kita Ward, the minimum temperature is forecast to drop to -4℃ for several days starting February 4, marking an unusually cold spell in recent years.

In Japan, each month in the lunar calendar has been given a unique traditional name known as Wafu Getsumei (Japanese-style month names). February is called Kisaragi (如月), which is said to originate from Kisaragi (衣更着), meaning “adding more layers of clothing.” This name reflects the lingering cold weather during this month, requiring people to wear extra layers for warmth.