Earlywood blue intensity of Picea purpurea reveals June minimum temperature variability in Eastern Tibetan Plateau since 1671CE

Temperature variations exhibit significant regional and seasonal differences, necessitating comprehensive research on different temperature variables across diverse areas. This study established an Earlywood Blue Intensity (EWBI) chronology of Picea purpurea in the eastern Tibetan Plateau (TP) and reconstructed the regional minimum temperature (Tmin) of June spanning from 1671 to 2007. The reconstruction, which accounted for 65 % of the variance during the calibrated period (1961–2007), revealed a period of relative stability in the 19th century and significant warming since the 1970s. The study indicated that the potential driving factors of the regional Tmin variation were El Niño-Southern Oscillation (ENSO) and tropical volcanism. Furthermore, we highlight that when a tropical volcanic eruption occurred without an El Niño event, the cooling effect on Tmin in the TP was significantly greater than when El Niño events occurred. A comparison between the reconstructed Tmin and mean maximum temperature (Tmax) series for the region revealed that the low-frequency variations of both series were generally consistent prior to 1900, while a pronounced asymmetry appeared in recent decades, with Tmin changes occurring earlier and exhibiting a more substantial warming trend.