[A-CG42] 地球規模環境変化の予測と検出

[ACG42-04] Nonmonotonic changes in the El Niño–Southern Oscillation under multiple scenarios until the 25th century in MIROC-ES2L

*林 未知也¹、横畠 徳太¹、小倉 知夫¹、塩竈 秀夫¹、Stuecker Malte^2,3、Zhao Sen⁴、Jin Fei-Fei^4,3 (1.国立環境研究所地球システム領域、2.米国ハワイ大学マノア校海洋学科、3.米国ハワイ大学マノア校国際太平洋研究センター、4.米国ハワイ大学マノア校大気科学科)

キーワード：エルニーニョ南方振動、地球システムモデル、共通社会経済経路、MIROC-ES2L

The El Niño–Southern Oscillation (ENSO) is the dominant interannual variability in the tropical Pacific. The majority of climate models project ENSO amplification in the 21st century despite high uncertainty, but the relationship between ENSO and climate change beyond the 21st century is not yet well understood. Here, the ENSO change is examined based on eight Shared Socioeconomic Pathway (SSP) scenario experiments using MIROC-ES2L extended until the end of the 25th century. Using an ENSO index, defined by interannual anomalies of the sea-surface temperature (SST) averaged in the Niño-3.4 region, we found that the 50-year running variance of the ENSO index is amplified until the global warming level (GWL) reaches 2°C approximately regardless of scenarios but decreases once the GWL exceeds 3°C under higher emission scenarios. Furthermore, the dominant peak in the ENSO power spectrum shifts to a higher frequency at elevated GWLs in higher emission scenarios. A permanent El Niño-like background condition caused by high GWL drastically reduces the occurrences of extreme El Niño events while moderate La Niña events continue to occur with anomalously intensified trade easterlies. Consequently, the ENSO index becomes negatively skewed at high GWLs, and the peak of anomalous SST tends to shift westward, reminiscent of more frequent central-Pacific ENSO events. The results indicate that various ENSO properties such as amplitude, frequency, asymmetry, and diversity may change nonlinearly with respect to the increase in global mean temperature.