[A-CG43] 北極域の科学

[ACG43-03] 人間活動によるエアロゾルの増大と自然に生じる気候変動が重なって20世紀中頃に北極が寒冷化していた

*相澤 拓郎^1,2、大島 長²、行本 誠史² (1.国立極地研究所、2.気象庁気象研究所)

キーワード：北極寒冷化、人為起源エアロゾル、数十年規模の内部変動、気候モデル、マルチモデル解析、北極温暖化

In the Arctic, observed decadal mean surface air temperatures (SATs) were 0.70°C–0.95°C lower around 1970 than those around 1940. The 35-multimodel ensemble mean of historical simulations in the Coupled Model Intercomparison Project Phase 6 (CMIP6) exhibited Arctic surface cooling trend in 1940–1970, which could be attributed to external forcings. Multimodel ensemble means of CMIP6 Detection and Attribution Model Intercomparison Project (DAMIP) historical simulations exhibited Arctic surface cooling of −0.22°C (±0.24°C) in 1970 versus 1940 and showed that anthropogenic aerosol forcings contributed to a cooling of −0.65°C (±0.37°C), which was partially offset by a warming of 0.44°C (±0.22°C) due to well-mixed greenhouse gases. In addition to the anthropogenic aerosol forcings, multidecadal internal variability with a magnitude of 0.47°C was the component primarily contributing to the observed Arctic cooling. We identified a spatial pattern of pan-Arctic multidecadal cooling due to the internal variability that resembles the 1940–1970 cooling pattern. As anthropogenic sulfur emissions and sulfate aerosols will decrease in any future scenarios of shared socioeconomic pathways (SSPs), Arctic warming will continue over the near-term future even under strong cooling fluctuations generated by internal variability.