なぜ気候モデルは極域の温暖化を過小評価するのか?見えない雲」がその答えかもしれない(Why do climate models underestimate polar warming? ‘Invisible clouds’ could be the answer)

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2023-11-08 ニューサウスウェールズ大学(UNSW)

◆UNSW Sydneyの研究者は、北極上空の成層圏雲が、気候モデルと実際の温暖化観測との間の差異を説明する可能性があることを発見しました。地球の平均表面温度の上昇に伴い、極域での温暖化が特に顕著ですが、気候モデルはこれらの地域での温暖化を依然として過小評価しています。これは過去の気候や将来の予測にも影響を及ぼす可能性があります。
◆成層圏雲は高高度で形成され、地球の表面を温める効果がありますが、気候モデルには通常含まれていません。研究は、成層圏雲の存在が気候モデルの不足を一部説明し、極域での温暖化を正確に再現するためにはより詳細なモデルが必要であることを示唆しています。

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北極圏の成層圏雲は、低地形と高メタンによって北極圏の温暖化を促進した。 Early Eocene low orography and high methane enhance Arctic warming via polar stratospheric clouds

Deepashree Dutta,Martin Jucker,Steven C. Sherwood,Katrin J. Meissner,Alex Sen Gupta & Jiang Zhu
Nature Geoscience  Published:07 November 2023
DOI:https://doi.org/10.1038/s41561-023-01298-w

なぜ気候モデルは極域の温暖化を過小評価するのか?見えない雲」がその答えかもしれない(Why do climate models underestimate polar warming? ‘Invisible clouds’ could be the answer)

Abstract

Proxy data suggest that the early Eocene (∼56–47.8 million years ago) was characterized by a much weaker equator-to-pole temperature gradient than today. However, general circulation models consistently underestimate high-latitude temperatures indicated by proxy records, suggesting that they may miss important processes. Previous studies hypothesized that wintertime polar stratospheric clouds may have played an important role in Arctic warming through greenhouse forcing, but these studies did not consider the effects of atmospheric chemistry or the early Eocene topography. Here we examine these factors using a high-top atmospheric model with interactive chemistry. The lower orography in the low- to mid-latitude Northern Hemisphere early Eocene weakens the stratospheric circulation which, in combination with sufficiently high methane concentrations, leads to a substantial increase in polar stratospheric clouds in the Arctic winter. Furthermore, an increase in early Eocene polar stratospheric clouds due to a 16- to 64-fold higher than pre-industrial methane concentration results in a radiative forcing larger than the direct greenhouse effect from the methane itself. This polar stratospheric cloud-induced radiative forcing could cause up to 7.4 K of Arctic surface warming. These results point to the potential for nonlinear interactions between individual forcings.

1702地球物理及び地球化学
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