世界の氷河、２１００年までに半減の可能性

【ワシントンＡＦＰ＝時事】世界の気温上昇を産業革命前と比べ１．５度に抑えるとする「パリ協定」の努力目標を達成した場合でも、世界にある２１万５０００の氷河のうち、４９％が２１００年までに消滅する可能性があるとする研究結果が５日、米科学誌サイエンスに発表された。（写真は資料写真）
　小さな氷河から消滅していくため、質量としては約２６％に相当するという。
　研究では、世界の平均気温がそれぞれ１．５度、２度、３度、４度上昇した場合の４通りのシナリオを検討した。
　現在の予想では、実際には２．７度上昇すると考えられている。その場合、欧州中部、カナダ西部、米国、ニュージーランドの氷河はほぼ完全に失われるという。
　論文の共著者であるオスロ大学とアラスカ大学フェアバンクス校に所属するレジーヌ・ホック氏は「欧州のアルプス、コーカサス地方、アンデス、米国西部のような氷河の比較的少ない地域では、どのような温暖化シナリオをたどっても今世紀末までにほぼ全ての氷河が失われる」「つまりこれらの氷河は多かれ少なかれ絶望的だ」と述べた。
　また、気温上昇が４度という最悪のシナリオの場合、アラスカにあるような巨大な氷河も影響を受け、今世紀末には氷河全体の８３％が消滅するとしている。
　数十年にわたる氷河の質量観測とコンピューターシミュレーションによって導き出された今回の予測は、国連の気候専門家のものよりも悲観的だが、ホック氏は「人間の行動によって質量減少を抑えることは可能だ」と指摘した。
　「実際にそれが起きるかどうかは別の問題で、それはむろん政策決定者次第だ」【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2023/01/06-17:28）

Half of the Earth's glaciers, notably smaller ones, are destined to disappear by the end of the century because of climate change, but limiting global warming could save others, according to a new study.
The findings, published in the journal Science on Thursday, provide the most comprehensive look so far at the future of the world's 215,000 glaciers.
The authors emphasized the importance of restricting greenhouse gas emissions to limit the consequences from glacier melt such as sea level rise and depletion of water resources.
To help orient policy makers, the study looked at the impact of four scenarios on glaciers, where global mean temperature change is 1.5 degrees Celsius (2.7 degrees Fahrenheit), 2.0C, 3.0C and 4.0C.
Every degree increase produces more melt and loss, said Regine Hock of the University of Oslo and University of Alaska Fairbanks, a co-author of the study.
But that also means if you reduce the temperature increase, you can also reduce that mass loss, Hock told AFP. So in that sense, there is also a little bit of hope.
Even if global temperature rise is limited to 1.5C above pre-industrial levels -- the most ambitious goal of the Paris Agreement -- the researchers estimated that 49 percent of the world's glaciers would vanish by the year 2100.
That would represent about 26 percent of the world's glacier mass because the smallest glaciers would be those first impacted.
Global mean temperature is currently estimated to be increasing by 2.7C which would result in a near-complete loss of glaciers in Central Europe, Western Canada and the continental United States and New Zealand.
Regions with relatively little ice like the European Alps, the Caucasus, the Andes, or the western US, they lose almost all the ice by the end of the century almost no matter what the emission scenario is, Hock said. So those glaciers, they're more or less doomed.
- 'Up to the policy makers' -
Under the worst-case scenario -- global temperature rise of 4.0C -- giant glaciers such as those in Alaska would be more affected and 83 percent of glaciers would disappear by the end of the century.
Glacier loss would also exacerbate sea level rise.
The glaciers that we are studying are only one percent of all ice on Earth, said Hock, much less than the Greenland ice sheet and the Antarctic ice sheet.
But they have contributed to sea level rise almost just as much as the Greenland and Antarctic ice sheet together in the last three decades, she said.
Warming of 1.5C would lead to an increase in average sea levels of nine centimeters while temperatures 4.0C higher would cause 15 centimeters of sea level rise.
It doesn't sound very much, nine centimeters up to 15 centimeters, Hock said, but it's not global sea level that is that much of a concern.
It's mostly associated storm surges, she said, which have the potential to cause a lot more damage.
The disappearance of glaciers will also have an impact on water resources because they provide freshwater for some two billion people.
The glaciers compensate for the loss of water in summer when it's not raining much and it's hot, Hock said.
The study's projections, which are more pessimistic than those of UN climate experts, were reached through observations of the mass of each glacier through the decades and computer simulations.
Despite the alarming findings, Hock said it is possible to reduce the mass loss by human action.
If it happens is of course a different question, she said. If that happens is of course up to the policy makers.