アマゾン森林火災でアンデス山脈の氷河融解が加速、研究

【パリＡＦＰ＝時事】南米にある世界最大の熱帯雨林アマゾンの森林火災によってアンデス山脈の氷河の融解が進み、数千万人が水不足に苦しむようになる恐れがあるとの研究結果が28日、英科学誌ネイチャーの関連オンライン学術誌「サイエンティフィック・リポーツ」に掲載された。（写真はブラジル北西部ロンドニア州で、アマゾン森林火災により立ち上る煙。航空機から撮影）
　アマゾン盆地では今年大規模な森林火災が発生し、地平線を煙が覆う写真が世界中で報じられて話題を呼んだ。
　今回の一連の火災は、農作物栽培や放牧を目的とした土地開墾など、人為的な要因で発生したものだ。だが、過去１０年間で最悪のペースで進む熱帯雨林の破壊が、被害を拡大した。２８日に発表されたブラジル政府統計（確報値）によると、２０１９年７月までの１２か月間に破壊されたアマゾンの森林面積は前年比４３％増となる１万１００平方キロに達している。２００８年以来最悪の規模だ。
　ブラジル・リオデジャネイロ州立大学のニュートン・マガリャエス・ネト氏のチームは、アマゾンの密林を焼く火災の煙がアンデス山脈の氷河に影響を及ぼしている可能性に着目。煙に含まれるすすが、卓越風に運ばれて数百キロ離れた場所で雪や氷の中に閉じ込められているのではないかとみて、研究を行った。
　森林火災が多く発生した２００７～２０１０年について観察しモデル化したところ、すすを含んだ氷河の表面の色が黒ずむことで氷河の融解が加速する可能性が明らかになった。黒色炭素粒子を含んだ氷河の表面は、太陽光を反射する割合（アルベド）が低下し、融解量は最大１４％増加するという。
　アンデス山脈の氷河を水源として頼る人々は７５００万人以上。地域の農家は最たる例で、雪解け水は食料生産に不可欠な存在だ。氷河の融解が加速すれば、農耕期が短くなり、飲料水も足りなくなって、しまいには減りゆく天然資源をめぐって紛争が起きかねないと研究チームは指摘している。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2019/12/02-08:43）

Fires in the Amazon rainforest are likely to increase the rate of melting of Andean glaciers, potentially disrupting water supply for tens of millions of people, scientists said on Thursday.
Images of smoke-filled horizons from blazes burning out of control across the Amazon basin made headlines around the world earlier this year.
The fires are started deliberately, often by farmers clearing land for grazing or crops, and are made significantly worse by deforestation -- a phenomenon currently at its highest level in a decade.
A team of researchers in Brazil studied the effect that smoke from the fires might have on glaciers in the Andes -- prevailing winds carry dust particles hundreds of kilometres, allowing them to be trapped in snow and ice.
Based on observations and modelling of fires between 2007-2010 -- a peak period -- the team found that aerosols from burning had the potential to increase glacier melting by darkening their surface colour.
Pollutants such as black carbon and dust lodged in the ice reduce the glacier's ability to reflect sunlight -- known as its albedo -- speeding the rates of melting by up to 14 percent.
More than 75 million people rely on water from Andean glaciers, including farmers in the region, meaning the seasonal melt is vital for food supply.
Faster melting could therefore shorten crop-growing periods, limit supplies of drinking water and eventually lead to conflicts over the dwindling resources, said the authors of the study, published in Nature Scientific Reports.
This cannot be considered a regional issue, said Newton de Magalhaes Neto, from Rio de Janeiro State University's Institute of Geography.
Instead it has social implications at a continental scale.
And there is likely to be a correlation between deforestation, where vast swathes of land are razed to grow crops or raise cattle, and glacier melt rates, as global food demand rises.
Considering the proximity of the Amazon basin to the tropical Andean glaciers and the dimensions of Amazonian biomass burning we expect greater melt rates as more Amazon gets deforested, Neto told AFP.
The Intergovernmental Panel on Climate Change in September warned that glaciers were losing 280 billion tonnes of ice every year, contributing 35 percent of sea level rises.
Neto said the main threat to the Andean glaciers was still climate change, as warmer oceans would contribute to the Amazon drying out, meaning fires would spread further.