California Temperature Since 1520 CE Shows Interactions in Extremes of Heat, Drought, and Fire

Abstract Summer maximum temperatures () in the Sierra Nevada have risen rapidly since the turn of the 20th century, especially above 1,500 m where trends in the south exceed 3°C century −1 . To place this warming into context, we developed a 504‐year reconstruction of growing‐season (April–September) (1520–2023 CE) from blue‐intensity and maximum latewood‐density data at nine high‐elevation conifer sites. The model explains 60% of instrumental variance () and shows that the 20th–21st centuries were the warmest of the past five. The warmest year is 2021 (+2.38°C), while four of the five coldest years coincide with major volcanic eruptions. Since 1980, mean summer increased 1.14°C (; 0.026°C yr −1 ), concurrent with declining PDSI and a threefold rise in compound hot–dry‐fire years. Dynamic regression suggests a shift from snowpack‐buffered to temperature‐dominated soil‐moisture regimes after 1900. These results show that post‐1980 warming and unprecedented compound extremes mark a new era of temperature‐driven ecological vulnerability in the Sierra Nevada.