温暖化の進行、従来想定より急速　新気候モデルで明らかに

【パリＡＦＰ＝時事】フランスの主要科学機関が新たに作成した2つの気候モデルにより、主に化石燃料の燃焼で大気中に排出された温室効果ガスによる地球表面温度の上昇が、これまで考えられていたより急速に進んでいるとの計算結果が示された。（写真は資料写真）
　両モデルはピエール・シモン・ラプラス研究所気候モデルセンターとフランス国立気象研究センターがそれぞれ作成したもので、パリで１７日に発表された。
　両モデルによると、炭素排出が現在の水準で続いた場合、産業革命以前の水準と比べた平均気温の上昇幅は２１００年までに７．０度に達する可能性がある。この値は気候変動に関する政府間パネル（ＩＰＣＣ）が２０１４年に公表し、これまで指標とされてきた第５次評価報告書（ＡＲ５）での同条件の予測よりも２度高い。
　ＩＰＣＣが２０２１年に発表する次回の主要報告は、「第６期結合モデル相互比較プロジェクト（ＣＭＩＰ６）」と総称される３０余りのモデルに基づき作成される予定で、今回発表された２つのモデルもここに含まれる。
　地球温暖化対策の国際枠組み「パリ協定」は、産業革命以前からの気温上昇を２度よりも「十分低く」抑え、可能であれば１．５度以下にするとの目標を定めたが、新たな計算結果から科学者らは、目標達成は楽観的に見ても困難だとしている。
　ＩＰＳＬ気候モデルセンターのオリビエ・ブシェール所長はＡＦＰに対し、これまで気温上昇幅を２度以下に抑える目標の達成が可能とされてきた「ＳＳＰ１　２．６」と呼ばれるシナリオでは「不十分」であることが、２つのモデルで示されたと述べた。
　英インペリアル・カレッジ・ロンドン准教授で、ＩＰＣＣ報告の主筆者の一人でもあるユーリ・ロゲル氏は、重要な不確実性は残るものの、ＣＭＩＰ６にモデル作成における最新の改善点が織り込まれていることは明らかだとＡＦＰに述べた。
　一連の改善点には、スーパーコンピューターの能力が向上したことや、気候システム、自然由来および人工の微粒子、温暖化に伴う雲の変化がより正確に表現されるようになったことなどがある。
　前出のブシェール氏もモデルが改善されたと指摘。新モデルについて「より精密で、現在の気候の傾向をより正確に再現している」と述べた。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2019/09/19-08:34）

Greenhouse gases thrust into the atmosphere mainly by burning fossil fuels are warming Earth's surface more quickly than previously understood, according to new climate models set to replace those used in current UN projections, scientists said Tuesday.
By 2100, average temperatures could rise 7.0 degrees Celsius above pre-industrial levels if carbon emissions continue unabated, separate models from two leading research centres in France showed.
That is up to two degrees higher than the equivalent scenario in the Intergovernmental Panel for Climate Change's (IPCC) 2014 benchmark 5th Assessment Report.
The new calculations also suggest that the Paris Agreement goals of capping global warming at well below two degrees, and 1.5C if possible, will be challenging at best, the scientists said.
With our two models, we see that the scenario known as SSP1 2.6 -- which normally allows us to stay under 2C -- doesn't quite get us there, Olivier Boucher, head of the Institute Pierre Simon Laplace Climate Modelling Centre in Paris, told AFP.
With only one degree Celsius of warming so far, the world is coping with increasingly deadly heat waves, droughts, floods and tropical cyclones made more destructive by rising seas.
A new generation of 30-odd climate models known collectively as CMIP6 -- including the two unveiled Tuesday -- will underpin the IPCC's next major report in 2021.
CMIP6 clearly includes the latest modelling improvements, even as important uncertainties remain, Joeri Rogelj, an associate professor at Imperial College London and an IPCC lead author, told AFP.
These include increased supercomputing power and sharper representations of weather systems, natural and man-made particles, and how clouds evolve in a warming world.
We have better models now, said Boucher. They have better resolution, and they represent current climate trends more accurately.
- 'Tipping points' -
A core finding of the new models is that increased levels of CO2 in the atmosphere will warm Earth's surface more -- and more easily -- than earlier calculations had suggested.
If confirmed, this higher equilibrium climate sensitivity, or ECS, means humanity's carbon budget -- our total emissions allowance -- is likely to shrink.
The French models are the first to be released.
The French modelling groups are to be congratulated for being the first to complete their simulations, said Piers Forster, director of the Priestley International Centre for Climate at the University of Leeds.
But other models developed independently have come to the same unsettling conclusion, Boucher confirmed.
The most respected ones -- from the United States, and Britain's Met Office -- also show a higher ECS than the previous generation of models, he said.
This is bad news for the fight against global warming, which continues to face strong political headwinds and institutional inertia despite a rapid crescendo of public awareness and concern.
A higher ECS means a greater likelihood of reaching higher levels of global warming, even with deeper emissions cuts, Boucher and two British scientists -- Stephen Belcher from the UK Met Office and Rowan Sutton from the UK National Centre for Atmospheric Science -- wrote in a blog earlier this year, tiptoeing around the implications of the new models.
Higher warming would allow less time to adapt and mean a greater likelihood of passing climate 'tipping points' such as thawing of permafrost, which would further accelerate warming.
A third to 99 percent of top-layer permafrost could melt by 2100 if carbon pollution is not abated, releasing billions of tonnes of greenhouse gases into the air, according to a draft IPCC special report on oceans and Earth's frozen zones obtained by AFP.
Unfortunately, our global failure to implement meaningful action on climate change over recent decades has put us in a situation where what we need to do to keep warming to safe levels is extremely simple, said Rogelj.
Global greenhouse gas emissions need to decline today rather than tomorrow, and global CO2 emissions should be brought to net zero.
The 2014 basket of climate models show Earth warming on current trends an additional 3C by 2100, and at least 2C even if national carbon cutting pledges are all met.
The two French climate models, including one from France's National Centre for Meteorological Research (CNRM), were unveiled at a press conference in Paris.