スイスの氷河、１９３１年から半減　研究チーム

【ジュネーブＡＦＰ＝時事】スイスの研究チームは２２日、国内の氷河の量が１９３１年の水準から半減したとする研究論文を公表した。（資料写真）
　論文をまとめたのはスイス連邦工科大学チューリヒ校と連邦森林・雪・景観研究所（ＷＳＬ）の研究チーム。欧州地球科学連合（ＥＧＵ）の専門誌「Ｔｈｅ Ｃｒｙｏｓｐｈｅｒｅ（雪氷圏）」に掲載された。
　気候変動が要因とされるアルプス山脈などの氷河の急速な融解は、２０００年代前半以降、より詳細に観測されるようになった。しかし、２０世紀中の氷河の変化についてはほぼ分かっておらず、継続的に観測されてきた氷河はごくわずかで、氷の推量モデルもまちまちだった。
　研究では、スイスの氷河の約８６％について、１９１６～１９４７年に撮影された写真約２万１７００枚を分析。撮影時期はまちまちだったため、１９３１年を基準年として、画像に基づきすべての氷河を再現していった。
　論文の筆頭執筆者エリック・シット・マナーフェルト氏は「二つの異なる時点での氷河の形状が分かれば、量の違いを算定できる」と説明した。
　研究チームは「再現した氷河の形状と、２０００年代のデータとを比較した結果、１９３１年から２０１６年の間に氷河の量は半減したと結論付けた」としている。
　研究によると、過去１００年間に氷河は継続的に減少したわけではなく、１９２０年代と１９８０年代には、量が増えた時期もあった。
　ただ１９３１～２０１６年を通じて見れば、氷河は大幅に縮小。現在は縮小ペースがさらに加速している。
　スイス氷河モニタリングネットワーク（ＧＬＡＭＯＳ）は、２０１６年以降の６年間だけでさらに１２％の氷河が失われたと指摘している。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2022/08/24-13:52）

Swiss glaciers have shed half their volume since 1931, Swiss researchers said Monday, following the first reconstruction of the country's ice loss in the 20th century.
Rapid glacier melt in the Alps and elsewhere, which scientists say is driven by climate change, has been increasingly closely monitored since the early 2000s. However, until now there has been little insight into how glaciers changed prior to that during the 20th century, with only a handful of individual glaciers tracked over time, and with different models for estimating their volume.
But Swiss researchers from the ETH Zurich technical university and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL say they had now reconstructed the topography of all Swiss glaciers in 1931, making it possible to show how they have evolved.
Based on these reconstructions and comparisons with data from the 2000s, the researchers conclude that the glacier volume halved between 1931 and 2016, they said in a statement.
Their study, published in the scientific journal The Cryosphere, used material from the TerrA image archive, which covers about 86 percent of Switzerland's glacierised area, analysing around 21,700 photographs taken between 1916 and 1947.
- Dramatic change -
For their reconstruction, the glaciologists used so-called stereophotogrammetry -- a technique used to determine the nature, shape and position of any object on the basis of image pairs.
If we know the surface topography of a glacier at two different points in time, we can calculate the difference in ice volume, lead study author Erik Schytt Mannerfelt said in the statement.
The researchers presented side-by-side picture pairs showing the same spot nearly a century apart, indicating the dramatic change that has taken place.
The Fiescher Glacier, for instance, resembled a massive sea of ice in 1928, but in 2021, a few tiny specs of white were all that remained on the lush green mountainside.
Since the images used for the reconstruction were taken in different years, the study used the mean year 1931 as a reference and reconstructed the surface topography of all glaciers for that year, the statement said.
In their statement, the researchers stressed that glaciers did not continuously recede over the past century, pointing out that there was even sporadic mass glacier growth in the 1920s and 1980s.
But while there may have been growth over short-term periods, Daniel Farinotti, a glaciology professor at ETH Zurich and WSL and co-author of the study, said it was important to keep the big picture in mind.
Our comparison between the years 1931 and 2016 clearly shows that there was significant glacial retreat during this period, he said in the statement.
And the total glacier volume is decreasing at an ever faster rate.
While Swiss glaciers lost half their volume in the 85 years leading up to 2016, the Swiss glacier monitoring network, GLAMOS indicates that they lost a further 12 percent in the following six years alone.
Farinotti said the evidence was clear: Glacier retreat is accelerating.