Attributing and projecting record-shattering September tropical night events in East Asia

In 2024, East Asia experienced an unprecedented nighttime heatwave during the summer. This study analyzes the features of 2024 tropical night events in July-August (JA) and September (SEP) and projects their future occurrence under different global warming levels (GWLs). The analysis reveals that the daily minimum temperature and specific humidity reached unprecedented levels in both JA and SEP in 2024, remarkable in SEP with breaking records by four or more standard deviations. Based on Coupled Model Intercomparison Project phase 6 (CMIP6) simulations, the 2024-like tropical night events exhibit zero probability of occurring under the historical climate with natural forcing only and remain rare even under historical climate involving anthropogenic forcing, particularly for SEP tropical night. Under future warming scenarios, the return period of 2024-like event drastically shortens, reaching 71, 10, and 2.5 years at 1.5 °C, 2.0 °C, and 2.5 °C GWL, respectively, implying that such events could become frequent and nearly regular event under higher warming levels. In addition to the anthropogenic forcing, internal variability contributed substantially to the extreme tropical nights through the expansion of the Western North Pacific Subtropical High and the South Asian High, driven by enhanced convection over the Philippine Sea and the northern Indian Ocean, respectively.