Abnormal weather - Ijōkishou (English spelling) unusual weather

Japanese: 異常気象 - いじょうきしょう（英語表記）unusual weather

A rare weather condition that occurs approximately once every 30 years or more. It is characterized by meteorological factors such as air pressure, temperature, and precipitation.

Before World War II, the term "abnormal weather" was commonly used to describe atmospheric phenomena that caused various meteorological disasters. Any weather phenomenon that was conspicuous and related to humans, such as typhoons or moving high pressure systems that brought about late frosts, was called abnormal weather. Even today, the term is sometimes used in this general sense.

After the Second World War, Japan was frequently hit by typhoons, which the occupying forces gave feminine names in English, and caused great damage. In order to keep a record of these typhoons, the Central Meteorological Observatory (now the Japan Meteorological Agency) compiled the "Abnormal Weather Report." Most of the contents of this report were compilations of various documents and surveys related to typhoons. It was only in the early 1960s that the term "abnormal weather," which had been used in this way with a very vague meaning, began to have a special meaning.

In January 1963, the monthly mean atmospheric pressure around Japan was about 10 hectopascals lower than normal, but this deviation from the normal value was about five times the standard deviation, and assuming a normal distribution, this would be an abnormally low pressure that occurs about once every 100,000 years. On the other hand, the monthly mean atmospheric pressure in Greenland and Iceland was more than 25 hectopascals higher than the normal value, which was also more than five times the standard deviation for the area. This large deviation in the monthly mean atmospheric pressure in the Northern Hemisphere was caused by an extremely rare atmospheric pressure pattern that continued in the Northern Hemisphere for over a month. Research on paleoclimatology that was being conducted at the time revealed that this atmospheric pressure pattern was similar to that of the Ice Age, and considering the situation in the Eastern Arctic Ocean, where a significant drop in temperature occurred in the 1960s, there was concern at the time that if this fluctuation continued, the Ice Age would return in the near future.

However, in the 1970s, the trend in temperature fluctuations in the Arctic Ocean began to rise, and global warming has accelerated over the 20 years from 1990 to 2010. Although we have not seen any abnormal atmospheric pressure patterns on the scale of January 1963, rare abnormal weather events that occur once every hundreds or thousands of years, far beyond the lower limit of abnormal weather that occurs once every few decades, continue to occur in various forms every year, including extremely hot summers, cold summers, warm winters, cold winters, heavy snowfall, droughts, prolonged rains, and lack of sunlight. What is also attracting attention is the fact that this abnormal weather is having a major impact on human survival on a global scale, not only on socio-economic activity, but also through water and food issues.

The main characteristics of abnormal weather in Japan and around the world since the 1970s can be noted as follows:

(1) Two extreme conditions, such as high temperature and low temperature, or little rain and heavy rain, coexist in time and space.

(2) The more significant the rarity, the larger the scale of the extreme weather event will be in both time and space.

(3) As global warming progresses, the occurrence of abnormally high temperatures has increased significantly, while the occurrence of abnormally low temperatures has been decreasing.

[Junkichi Nemoto and Takashi Aoki]

Cause

Climate fluctuates on a scale of several years, such as the El Niño/Southern Oscillation, and even on a scale of several decades. The Southern Oscillation is an atmospheric phenomenon discovered in the process of investigating the causes of irregular Indian summer monsoons and droughts, and is said to be linked to the El Niño phenomenon and cause abnormal weather all over the world. Phenomenologically, abnormal weather can be seen as a phenomenon that occurs when the climate system changes with a transition period. A transition period is considered to be a period in which the average climate conditions of the old and new systems coexist, and as long as the old system that we have already experienced is taken as the standard, abnormal weather seems to appear in a way that even if it is a very rare state, it is quite normal from the perspective of the new system. A further question is why such changes in the system are occurring. Various factors have been listed, but a comprehensive explanation of the causes has not yet been completed.

Presently, possible causes include natural terrestrial causes such as (1) long-term variations in the atmosphere's inherent climate, (2) changes in atmospheric composition (such as natural changes in carbon dioxide), (3) volcanic activity, (4) abnormalities in ocean surface temperatures, and (5) changes in the state of snow and ice in the polar regions.

Natural extraterrestrial causes include (1) changes in solar activity and (2) changes in the Earth's orbital elements.

In addition to these natural causes, there are currently anthropogenic causes caused by human activities that can be considered on a global scale, including (1) air pollution, (2) marine pollution, (3) artificial increases in carbon dioxide and freon gases, (4) the effects of modifying the natural environment, etc. The atmosphere, as one huge system, is considered to be subject to complex influences from each of the above factors.

[Junkichi Nemoto and Takashi Aoki]

"Abnormal Weather," edited by the Science Department of the Asahi Shimbun (1977, Asahi Shimbun)" ▽ "Preparing for Abnormal Weather," written by Asakura Tadashi (1981, Nihon Keizai Shimbun)" ▽ "Weather and Disasters," written by Nakajima Nobutaro (1986, Shincho Sensho)" ▽ "Measuring the Weather," written by Kobayashi Jutaro (1988, Japanese Standards Association)" ▽ "The Story of Weather," edited by Mitsuda Yasushi (1988, Gihodo Publishing)" ▽ "What is Happening on Earth? Abnormal Weather is Now on the Rise," written by Nemoto Junkichi (1989, Chikuma Shobo) ▽ "Abnormal Weather -- CFCs, Acid Rain, Deforestation, Global Warming," written by Yamamoto Ryuzaburo (1989, Shueisha)" ▽ "A Hotting Earth -- Concerns about Abnormal Weather Caused by Global Warming," written by Nemoto Junkichi (1989, Nesco)" ▽ "Abnormal Weather and Environmental Destruction" by Asakura Tadashi (1990, Yomiuri Shimbun)" ▽ "Handbook of Global Environmental Engineering, edited by the Editorial Committee for the Handbook of Global Environmental Engineering (1991, Ohmsha)" ▽ "Weather at the End of the Century" by Nemoto Junkichi (1992, Chikuma Shobo)" ▽ "The Great Harvest Famine of the Heisei Era, edited by the Agricultural Meteorological Society of Japan (1994, Agriculture and Forestry Statistics Association)" ▽ "Climate Change Will Change History" by Takahashi Koichi and Asakura Tadashi (1994, Maruzen)" ▽ "Atmosphere and Its Movement" by Maruyama Kento et al. (1995, Tokai University Press)" ▽ "Weather Question Box: Why Why Questions" based on the original work by Suzuki Kazuo (1996, Ministry of Finance Printing Bureau)" ▽ "Global Warming and Ozone Depletion" by Izumi Kunihiko (1997, Shin Nihon Shuppansha)" ▽ ``Food Security and the Agricultural Environment in the 21st Century'', edited by the Ministry of Agriculture, Forestry and Fisheries' National Institute for Agro-Environmental Sciences (1998, Yokendou )'' ▽ ``Weather Charts and Weather - How to Draw and Read Them'', written by Nozawa Gen'emon (1998, Seizando Shoten)'' ▽ ``How the Weather Works - Illustrated Trivia'', written by Olympus, edited by Muramatsu Teruo (1998, Natsume Shoten)'' ▽ ``Today's Meteorological Operations'', edited by the Japan Meteorological Agency, 1999 Edition (1999, Printing Bureau, Ministry of Finance) '' ▽ ``Interesting Weather Topics'', 4th Edition, written by Nozawa Gen'emon (1999, Seizando Shoten)'' ▽ ``Illustrated Quick Weather Book'' , written by Baba Kunihiko (2000, Kajisha)'' ▽ ``We've Come This Far! Environmental destruction: Useful for comprehensive learning 6: Abnormal weather and the future of the Earth (2000, Poplar Publishing) ▽ "Illustrated trivia: Abnormal weather" by Hosaka Naoki, supervised by Ueda Hiroaki (2000, Natsume Publishing) ▽ "Atmospheric environmental science: The meteorological and biological environments of the Earth" by Maki Taichi (2000, Asakura Publishing) ▽ "Typhoons and tornadoes: A comprehensive look at abnormal weather from avalanches to the El Niño phenomenon" by Jack Challoner, supervised by Hiranuma Yoji for the Japanese version (2000, Dohosha Publishing, Kadokawa Publishing) ▽ "Weather charts and meteorology books: When to look at, read, and write weather charts" revised new edition by Miyazawa Seiji (2001, International Geological Society) ▽ "El Niño and the global environment" revised and expanded edition edited by the Climate Impact and Utilization Research Group (2001, Seizando Publishing)" ▽ "Japan Meteorological Agency, ed., 'Current Meteorological Services -- Weather Information Services in the IT Era,' 2002 Edition (2002, Ministry of Finance Printing Bureau)" ▽ "Sumi Akimasa, 'El Niño and Global Warming,' (2003, Ohmsha)" ▽ "Saeki Michio, 'Learning about the El Niño Phenomenon,' revised and expanded edition (2003, Seizando Shoten)" ▽ "Japan Meteorological Agency, ed., 'Abnormal Weather Report 2005,' (2005)" ▽ "Nemoto Junkichi, 'Tracking Abnormal Weather,' (Chuko Shinsho)" ▽ "Nemoto Junkichi, 'The Ice Age is Coming -- Abnormal Weather Announces the Crisis of Humanity,' (Kobunsha Kappa Novels)" ▽ "Tsuchiya Iwao, 'Will the Earth Get Colder? -- The Little Ice Age and Abnormal Weather,' (Kodansha Gendai Shinsho)" ▽ "Murayama Mitsuji, 'Abnormal Weather -- What is Behind the Increase in Occurrence?' (Bestsellers Wani's New Shinsho)" ▽ "Extremely Abnormal Weather - From 30 Years of Records" by Nemoto Junkichi (Chuko Shinsho)" " A Book that Explains the Mysteries of Weather" by Shimamura Masaru and Yamauchi Toyotaro (Kosaido Bunko) " "How Abnormal Weather Progresses" by Asai Tomio (Shogakukan Bunko)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

およそ30年以上に1回という割合でまれに現れる気象状況。気圧、気温、降水量などの気象要素がその指標となる。

　異常気象ということばは、第二次世界大戦前は、さまざまな気象災害をもたらす大気現象に対し、ごく一般的に用いられていた。それは、台風や、晩霜をもたらす移動性高気圧など、なにか人間にかかわり合い目だつような気象はすべて異常気象とよばれていた。現在も一般的には、このような意味で用いられることもある。

　第二次世界大戦後、日本には、駐留軍が英語で女性名をつけた台風が頻繁に来襲し、被害を与えたが、これらの記録を残すために、当時の中央気象台（現、気象庁）でまとめられたものが『異常気象報告』であった。この報告の内容のほとんどは台風に関する諸資料、調査をまとめたものであった。このようにきわめて漠然とした内容をもつことばとして用いられてきた異常気象が、特別な意味をもつようになったのは、1960年代の初めからのことである。

　1963年（昭和38）1月、日本付近の月平均気圧は平年よりおよそ10ヘクトパスカルほど低くなったが、平年値からのこの偏りは標準偏差のおよそ5倍にあたり、正規分布を仮定すると、これはおよそ10万年に1回の異常低圧となるのである。他方、グリーンランド、アイスランド方面ではこの月の月平均気圧が平年値より25ヘクトパスカル以上も高くなり、これもその地域の標準偏差の5倍以上となった。北半球における月平均気圧のこのような大きな偏りは、きわめてまれな形の気圧配置が北半球に1か月余りにわたって持続したためにおこったことである。その気圧配置は、当時進められていた古気候学の研究から、氷河時代の気圧配置に類似していることが判明し、1960年代に顕著な気温の下降をみせた北極海の東半球側の状況から、このような変動がなお持続するなら、やがて近い将来に氷河時代が再来するのではないか、ということが当時懸念されたのである。

　しかしその後、1970年代になって北極海方面の気温変動の傾向は上昇に転じ、だいたい1990～2010年の20年間で温暖化が加速している。1963年1月ほどの異常気圧配置は現れてはいないが、数十年に一度といった異常気象の下限の線をはるかに超えた、何百年、何千年に一度といったまれな異常気象が、猛暑、冷夏、暖冬、寒冬、豪雪、干魃(かんばつ)、長雨、日照不足など、毎年さまざまに姿を変えながら現れ続けている。またその異常気象は、社会経済活動だけでなく、水と食糧の問題を介して、全地球的な規模で、人間の生存に対して大きな影響を与えている点が注目されているのである。

　1970年代以降の日本および世界のおもな異常気象の特徴点として次のことがあげられる。

(1)高温と低温、もしくは少雨と多雨というように、両極端の状態が時間的にも空間的にも共存する形で現れている。

(2)まれな程度が顕著になればなるほど、異常気象の規模は時間的にも空間的にもスケールが大きくなる。

(3)地球の温暖化に伴い、異常高温の発生の増加が顕著で、異常低温は減少傾向にある。

［根本順吉・青木　孝］

原因

気候はエルニーニョ／南方振動現象のような数年スケール、さらに長い数十年スケールでも変動している。南方振動現象とは、不順なインドの夏のモンスーン（季節風気候）と干魃の原因を探る過程で発見された大気の現象で、これとエルニーニョ現象が結び付いていて世界各地に異常気象を引き起こすといわれている。現象的には、異常気象は、気候の体系が遷移期間をもちながら変わっていくときに現れる現象とみることができる。遷移期間は旧体系と新体系の平均的な気候状態が共存する期間とみられるが、われわれがすでに経験してきた旧体系を標準とする限り、非常にまれな状態であっても、新しい体系からみるならば、ごく通常の状態であるというような形で異常気象は現れているように思われる。そこでさらに問われるのは、なぜそのような体系の変動がおこっているのかということである。これについてはさまざまな要因が列挙されるが、これを総合した原因の説明はまだできあがってはいない。

　さしあたり原因と考えられる事象をあげるならば、自然的地球内原因としては、(1)大気固有の気候の長い周期変動、(2)大気組成成分の変化（たとえば自然的な二酸化炭素の変化など）、(3)火山活動、(4)海洋の表面水温の異常、(5)極地の雪氷状態の変動、などがあげられる。

　また、自然的地球外原因としては、(1)太陽活動の変化、(2)地球の軌道要素の変化、があげられる。

　現在はこのような自然的原因のほかに、人間活動による人為的原因が全地球的規模で考えられるが、これについては、(1)大気汚染、(2)海洋汚染、(3)人為的な二酸化炭素やフレオンガス（フロンガス）の増加、(4)自然改造による影響、などがあげられる。大気は一つの巨大なシステムとして、以上の各要因から複雑な影響を受けていると考えられる。

［根本順吉・青木　孝］

『朝日新聞科学部編『異常気象』（1977・朝日新聞社）』▽『朝倉正著『異常気象に備える』（1981・日本経済新聞社）』▽『中島暢太郎著『気象と災害』（1986・新潮選書）』▽『小林寿太郎著『気象をはかる』（1988・日本規格協会）』▽『光田寧編著『気象のはなし』（1988・技報堂出版）』▽『根本順吉著『地球に何がおきているか――異常気象いよいよ本番』（1989・筑摩書房）』▽『山本龍三郎著『気象異常――フロン・酸性雨・森林破壊・温暖化』（1989・集英社）』▽『根本順吉著『熱くなる地球――温暖化が意味する異常気象の不安』（1989・ネスコ）』▽『朝倉正著『異常気象と環境破壊』（1990・読売新聞社）』▽『地球環境工学ハンドブック編集委員会編著『地球環境工学ハンドブック』（1991・オーム社）』▽『根本順吉著『世紀末の気象』（1992・筑摩書房）』▽『日本農業気象学会編著『平成の大凶作』（1994・農林統計協会）』▽『高橋浩一郎・朝倉正著『気候変動は歴史を変える』（1994・丸善）』▽『丸山健人他著『大気とその運動』（1995・東海大学出版会）』▽『鈴木一雄原作『お天気なぜなぜ質問箱』（1996・大蔵省印刷局）』▽『泉邦彦著『地球温暖化とオゾン層破壊』（1997・新日本出版社）』▽『農林水産省農業環境技術研究所編著『21世紀の食料確保と農業環境』（1998・養賢堂）』▽『能沢源右衛門著『天気図と気象――その描き方と見方』（1998・成山堂書店）』▽『村松照男監修、オリンポス著『気象のしくみ――図解雑学』（1998・ナツメ社）』▽『気象庁編『今日の気象業務』平成11年版（1999・大蔵省印刷局）』▽『能沢源右衛門著『気になる気象の話』四訂版（1999・成山堂書店）』▽『馬場邦彦著『図解早わかりお天気ブック』（2000・舵社）』▽『奈須紀幸監修、浅井冨雄編『ここまできた！　環境破壊――総合的な学習にやくだつ6　異常気象とこれからの地球』（2000・ポプラ社）』▽『植田宏昭監修、保坂直紀著『図解雑学　異常気象』（2000・ナツメ社）』▽『真木太一著『大気環境学――地球の気象環境と生物環境』（2000・朝倉書店）』▽『ジャック・シャロナー著、平沼洋司日本語版監修『台風と竜巻――なだれからエルニーニョ現象まで異常気象を一望する』（2000・同朋舎刊行、角川書店発売）』▽『宮澤清治著『天気図と気象の本――天気図を見るとき読むとき書くとき』改訂新版（2001・国際地学協会）』▽『気候影響・利用研究会編『エルニーニョと地球環境』改訂増補版（2001・成山堂書店）』▽『気象庁編『気象業務はいま――IT時代の気象情報サービス』2002年版（2002・財務省印刷局）』▽『住明正著『エルニーニョと地球温暖化』（2003・オーム社）』▽『佐伯理郎著『エルニーニョ現象を学ぶ』改訂増補版（2003・成山堂書店）』▽『気象庁編・刊『異常気象レポート2005』（2005）』▽『根本順吉著『異常気象を追って』（中公新書）』▽『根本順吉著『氷河期が来る――異常気象が告げる人間の危機』（光文社カッパ・ノベルス）』▽『土屋巌著『地球は寒くなるか――小氷期と異常気象』（講談社現代新書）』▽『村山貢司著『異常気象――多発する裏に何があるのか』（ベストセラーズ・ワニのnew新書）』▽『根本順吉著『超異常気象――30年の記録から』（中公新書）』▽『嶋村克・山内豊太郎著『天気の不思議がわかる本』（廣済堂文庫）』▽『浅井冨雄著『異常気象はこう進む』（小学館文庫）』

[参照項目] | 移動性高気圧 | エルニーニョ | 海洋汚染 | 干魃 | 気圧 | 気圧配置 | 気温 | 気候 | 気候変動 | 気象 | 気象災害 | 気象台 | 気象庁 | 季節風気候 | 降水量 | 豪雪 | 古気候学 | 霜 | 大気汚染 | 台風 | 暖冬 | 氷河時代 | フロン | 冷夏

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