都市のスプロール化は、地球温暖化を陸地上で揺り動かすのに十分な規模になった(City Sprawl Now Large Enough to Sway Global Warming Over Land)

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2024-06-18 パシフィック・ノースウェスト国立研究所(PNNL)

都市の拡大が大規模な温暖化にどれだけ影響を与えるかを調査した新しい研究が、雑誌「One Earth」に掲載されました。かつて都市化は地球の表面積が小さいため気候にほとんど影響しないと考えられていましたが、新たな研究は都市化が地球上の陸地の温暖化に明確な影響を与えていることを示しています。特に急速に都市化が進む地域で顕著です。例えば、中国の揚子江流域では、2003年から2019年にかけての温暖化の約40%が都市化によるものでした。日本では都市化が温暖化に25%寄与しており、ヨーロッパや北アメリカでは2〜3%の影響が見られました。全体として、都市は昼間に1.3%、夜間に1.1%の陸地の温暖化を引き起こしました。都市化は建物が熱を吸収・保持するため、都市部は農村部よりも気温が高くなりやすいです。都市の影響は地域や大陸規模で明らかであり、特にアジアなどの急速に都市化が進む地域で強い温暖化が観察されました。この研究は、都市の成長が気候に与える影響を理解し、気候モデルに都市の影響を組み込む重要性を強調しています。

<関連情報>

都市化が大陸から地域スケールの温暖化を悪化させる Urbanization exacerbates continental- to regional-scale warming

TC Chakraborty, Yun Qian
One Earth  Published: June 11, 2024
DOI:https://doi.org/10.1016/j.oneear.2024.05.005

Highlights

  • Massive increases seen in urban area throughout countries and continents
  • Urban warming signal has become strong enough to detect at larger scales
  • However, primary cause of global warming is still not urbanization
  • Given expected future urbanization, important to resolve these impacts

Science for society

Combining millions of satellite-derived images of land surface temperature (LST) with dynamic urban area estimates, we demonstrate that the urban influence on continental- to regional-scale warming has become more detectable over time, especially for rapidly urbanizing regions and countries in Asia. However, the main cause of global warming is still not urbanization, contributing to only around 2% of the land warming during the study period. We also estimate these large-scale urban warming signals under all shared socioeconomic pathways (SSPs) used to project global and regional climate change. Based on these results, we argue that, in line with other forms of land use/land cover change, urbanization should be explicitly included in future climate change assessments across scales. These patterns, also seen for air temperature, reframe our understanding of urbanization in the climate system from only a local-scale phenomenon to one with non-negligible regional- and even continental-scale impacts.

Summary

Urbanization is usually ignored when estimating past changes in large-scale climate and for future climate projections since cities historically covered a small fraction of the Earth’s surface. Here, by combining global land surface temperature observations with historical estimates of urban area, we demonstrate that the urban contribution to continental- to regional-scale warming has become non-negligible, especially for rapidly urbanizing regions and countries in Asia. Consequently, expected urban expansion over the next century suggests further increased urban influence on large-scale surface climate in the future (approximately 0.16 K for North America and Europe for high-emission scenario in 2100). Based on these results, also seen for air temperature, we argue that, in line with other forms of land use/land cover change, urbanization should be explicitly included in climate change assessments. This requires incorporation of dynamic urban extent and biophysics in current-generation Earth system models to quantify potential urban feedback on the climate system across scales.

Graphical abstract

都市のスプロール化は、地球温暖化を陸地上で揺り動かすのに十分な規模になった(City Sprawl Now Large Enough to Sway Global Warming Over Land)

1702地球物理及び地球化学
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