太陽光遮る温暖化対策、専門家６０人が禁止求める

【パリＡＦＰ＝時事】太陽光を反射する粒子を中層大気に大量散布して地表の温度を下げ、地球温暖化の影響を軽減する「太陽放射管理（ＳＲＭ）」と呼ばれる気候工学（ジオエンジニアリング）の手法について、６０人余りの政策研究者や科学者が１７日、潜在的な危険を伴うため政府レベルで禁止するべきだと呼び掛ける公開書簡を発表した。（写真は資料写真）
　書簡は、仮に数十億個の硫酸エアロゾルを散布して太陽光のほんの一部を狙い通り反射させられたとしても、その利益を相殺する結果が生じるだろうと述べている。
　学術誌「ＷＩＲＥｓ　Ｃｌｉｍａｔｅ　Ｃｈａｎｇｅ」の論評を添えた書簡は、「ソーラー・ジオエンジニアリング（太陽気候工学）を地球規模で公正かつ包摂的・効果的に運用・管理することは不可能だ」と指摘。
　「各国政府や国連（ＵＮ）その他の関係機関に対し、ソーラー・ジオエンジニアリングが気候変動対策の選択肢として標準化されるのを防ぐため、直ちに政治的行動を取るよう求める」と訴え、国家資金の投入や屋外での実験を禁止し、ＳＲＭ技術に関する特許権を認めないことなどを盛り込んだ「国際的な不使用協定」を締結するよう呼び掛けている。
　大量の反射性粒子を大気中に散布すると地球の温度が低下することは、以前から知られている。自然界でも同様の現象がしばしば起きており、フィリピンのピナツボ山が１９９１年に噴火した際には、地表の平均気温が１年以上にわたって下がった。
　一方で、太陽光を人為的に弱めるＳＲＭによって南アジアや西アフリカの降雨量が減り、農作物に大損害を与えて何億人もの人々の主食に影響する恐れがあることが、複数の研究で示されている。また、「気候変動に関する政府間パネル（ＩＰＣＣ）」は、「（ＳＲＭが）何らかの理由で中止された場合、地表温度が急上昇するのは確実だ」と指摘している。【翻訳編集ＡＦＰＢＢＮｅｗｓ】

〔ＡＦＰ＝時事〕（2022/01/18-11:35）

Planetary-scale engineering schemes designed to cool Earth's surface and lessen the impact of global heating are potentially dangerous and should be blocked by governments, more than 60 policy experts and scientists said on Monday.
Even if injecting billions of sulphur particles into the middle atmosphere -- the most hotly debated plan for so-called solar radiation modification (SRM) -- turned back a critical fraction of the Sun's rays as intended, the consequences could outweigh any benefits, they argued in an open letter.
Solar geoengineering deployment cannot be governed globally in a fair, inclusive and effective manner, said the letter, supported by a commentary in the journal WIREs Climate Change.
We therefore call for immediate political action from governments, the United Nations and other actors to prevent the normalisation of solar geoengineering as a climate policy option.
An increase of 1.1 degrees Celsius above mid-19th century levels has already boosted the intensity, frequency and duration of deadly heat waves, droughts and megastorms.
The world's nations have committed to capping the rise in Earth's surface temperature to 1.5C above mid-19th century levels, but UN-backed scientists have said that threshold will be breached, possibly within a decade.
The failure to reduce the greenhouse gas emissions that drive global heating has led some policy makers to embrace solar geoengineering -- widely dismissed not long ago as more science fiction than science -- in order to buy time for a more durable solution.
It has long been known that injecting a large quantity of reflective particles into the upper atmosphere could cool the planet.
Nature sometimes does the same: debris from the 1991 eruption of Mount Pinatubo in the Philippines lowered Earth's average surface temperature for more than a year.
But the open letter said there are several reasons to reject such a course of action.
Artificially dimming the Sun's radiative force is likely to disrupt monsoon rains in South Asia and western Africa, and could ravage the rain-fed crops upon which hundreds of millions depend for nourishment, several studies have shown.
- Unintended consequences -
Stratospheric sulfate injection weakens the African and Asian summer monsoons and causes drying in the Amazon, the Intergovernmental Panel on Climate Change (IPCC) said in its most recent scientific assessment.
Other regions, however, could benefit: a study last year concluded that SRM could sharply curtail the risk of drought in southern Africa.
Scientists also worry about so-called termination shock if seeding the atmosphere with Sun-blocking particles were to suddenly stop.
If SRM were terminated for any reason, there is high confidence that surface temperatures would increase rapidly, the IPCC said.
In addition, the technology would do nothing to stop the continuing buildup of atmospheric CO2, which is literally changing the chemistry of the ocean.
The open letter also cautions that raising hopes about a quick fix for climate can disincentivise governments, businesses and societies to do their upmost to achieve decarbonisation or carbon neutrality as soon as possible.
Finally, there is currently no global governance system to monitor or implement solar geoengineering schemes, which could be set in motion today by a single country, or even a billionaire with rockets.
The open letter calls for an international non-use agreement that would block national funding, bad outdoor experiments and refuse to grant patent rights for SRM technologies.
Such an agreement would not prohibit atmospheric or climate research as such, the letter said.
Signatories include Frank Biermann, a professor of global sustainability governance at Utrecht University; Aarti Gupta, a professor of global environmental governance at Wageningen University in The Netherlands; Professor Melissa Leach, director of the Institute of Development Studies in Sussex, England; and Dirk Messner, president of the German Environment Agency.