Global warming has been an ongoing phenomenon since the mid-20th century, with the Mediterranean basin identified as one of the major climate change hotspots. This study presents the 193-year-long thermal dataset (1833–2025) recorded at the Historical Meteorological Observatory of the University of Genoa (NW Italy), one of the longest continuous series in the country and part of the World Meteorological Organization (WMO) global network. The Mann–Kendall test (at 95% significance-level) was applied to identify statistically significant long-term temperature trends over the entire record and within subperiods corresponding to the last 150, 120, 90, 60, and 30 years. To evaluate variations in extreme events, a set of three ETCCDI-defined climatic indices was selected. Annual anomaly values were calculated with respect to both the mean of the entire period (1833–2025) and the WMO Climatological Standard Normals (1961–1990). The results identify a cold phase between 1880 and 1920 and indicate that the warmest period of the entire series has been ongoing since 2022. The Mann-Kendall test reveals a clear and consistent warming pattern, particularly during the cold season (November–March), with rates ranging from 0.005 to 0.010 °C yr−1. This warming has intensified in recent decades, with the 1996–2025 period exhibiting the strongest trends. Moreover, the frequency of tropical nights has increased significantly, while summer days have shown a significant increase only in the last 30 years. These results provide significant evidence of local thermal change, consistent with broader Mediterranean and global-scale temperature accelerations, providing key insights for adaptation strategies.
Brown carbon (BrC) is a light-absorbing component of organic aerosol that contributes to atmospheric radiative forcing by absorbing ultraviolet and visible light. Despite its climatic significance, long-term characterization of BrC in the Seoul Metropolitan Area remains limited, and previous studies have largely relied on single-solvent extraction approaches. Here, PM2.5 samples collected in Seoul from January 2019 to December 2023 were fractionated into water-soluble (WS-BrC) and water-insoluble (WIS-BrC) components via sequential water-methanol extraction, and their optical properties were characterized. Both fractions exhibited pronounced interannual variability, with absorption peaking in 2019, declining to a minimum in 2022, and rebounding in 2023. Seasonally, absorption coefficient (Abs365) peaked in winter (WS-BrC: 4.87 ± 1.68 Mm−1; WIS-BrC: 3.25 ± 0.97 Mm−1) and reached its minimum in summer (WS-BrC: 1.74 ± 0.99 Mm−1; WIS-BrC: 0.68 ± 0.29 Mm−1). Lower absorption Ångström exponent (AAE300–500) values in winter, together with a broader and higher AAE300−500 distribution in summer, and SHAP-based analysis of pollutants and meteorological parameters, indicated a seasonal shift in WS-BrC from primary combustion influences in winter to enhanced photochemical secondary formation in summer. WIS-BrC was associated with solid-fuel combustion and showed a negative SHAP response at high O3. Simple forcing efficiency over 300–700 nm was estimated for WS-BrC and WIS-BrC, with winter values of 4.34 ± 1.17 W g−1 and 4.47 ± 2.39 W g−1, respectively, comparable to combustion-influenced East Asian cities. These findings show that the climate relevance of urban BrC depends on seasonally varying chromophore composition and atmospheric processing, highlighting the limitations of assessments based solely on organic aerosol mass and the need for long-term monitoring.
