北極の気温は地球温暖化の4倍の速さで上昇している(Arctic temperatures are increasing four times faster than global warming)

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観測された気温を分析した結果、ほとんどの気候モデルで見落とされていた過去50年間の2つのジャンプが発見された Analysis of observed temperatures finds two jumps over the past 50 years that were missed by most climate models

2022-07-06 アメリカ・ロスアラモス国立研究所(LANL)

Since 1970, the Arctic has experienced a larger warming trend than most of the globe, leading to decreasing Arctic sea-ice cover, melting of the Greenland ice sheet and rising sea levels. Sudden jumps in temperatures in the region occur on a short timescale that is invisible to most climate models. Selecting the models that capture trends for 10- or 20-year periods can allow more accurate predictions of Arctic climate change and its effects. Credit: Dreamstime

観測された気温の新しい分析によると、北極は地球温暖化の速度の4倍以上の速度で加熱していることがわかりました。この傾向は、過去50年間に2回、急激に上昇し、39の気候モデルのうち4つを除くすべてのモデルで見落とされている。
この研究での増幅指数は、北極の21年間の気温推移と全球の21年間の気温推移の比である。
この研究では、21世紀初頭の数十年間で、北極圏の増幅指数は4以上となり、世界平均の4倍の速さと、30年から40年の時間間隔で行われたこれまでの研究結果よりもかなり速い速度であると算出した。
今後、北極と熱帯の温度差が小さくなるにつれて、北極の増幅指数の増加は小さくなる可能性がある。

<関連情報>

北極の年平均増幅率1970-2020年:CMIP6気候モデルによる観測とシミュレーション。 Annual Mean Arctic Amplification 1970–2020: Observed and Simulated by CMIP6 Climate Models

Petr Chylek,Chris Folland,James D. Klett,Muyin Wang,Nick Hengartner,Glen Lesins,Manvendra K. Dubey
Geophysical Research Letters  Published: 25 June 2022
DOI:https://doi.org/10.1029/2022GL099371

Abstract

While the annual mean Arctic Amplification (AA) index varied between two and three during the 1970–2000 period, it reached values exceeding four during the first two decades of the 21st century. The AA did not change in a continuous fashion but rather in two sharp increases around 1986 and 1999. During those steps the mean global surface air temperature trend remained almost constant, while the Arctic trend increased. Although the “best” CMIP6 models reproduce the increasing trend of the AA in 1980s they do not capture the sharply increasing trend of the AA after 1999 including its rapid step-like increase. We propose that the first sharp AA increase around 1986 is due to external forcing, while the second step close to 1999 is due to internal climate variability, which models cannot reproduce in the observed time.

Key Points
  • Annual mean Arctic Amplification (AA) within the period 1970–2020 changed in steep steps around 1986 and 1999. It reached values over 4.0
  • Even those CMIP6 models best at reproducing the AA did not reproduce the second sudden increase near 1999
  • We conjecture that the first AA sharp increase is due to external forcing, while the second is due to internal climate variability
Plain Language Summary

The rate of Arctic warming varied in time, while the rate of global warming was nearly constant over the period 1960–2020. This led to a variable Arctic Amplification (AA) defined as a ratio of the Arctic warming trend to mean global warming trend. In addition, the Arctic experienced sudden changes in the rate of warming with step-like changes in annual mean Arctic Amplification around the years 1986 and 1999. Climate models do not capture the second observed sharp increase of the AA. We suggest that the first AA increase around 1986 is primarily due to external forcing (increasing concentration of carbon dioxide) while the second sharp increase around 1999 is dominated by internal climate variability which current models cannot capture accurately within the time scale of the physical phenomena.

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