Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the ¹⁴C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct ¹⁴C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved ¹⁴C measurements are needed.

This contribution presents a near‐millennium‐long reconstruction of May–July (MJJ) precipitation for Bohemia, the western part of the recent Czech Republic. A well‐replicated chronology of oak (Quercus spp.) tree‐ring width (TRW) measurements covering the 1040–2013 period was employed as a high‐resolution hydroclimatic proxy. Standardized TRW indices were calibrated to selected grid points from the CRU precipitation database, covering the geographical distribution of the oak data used. The oak TRW chronology explains 34% of MJJ precipitation variability during the 1901–1980 period used for calibration. Although the relationship between oak TRW and target data was relatively stable for this period, the coherence drops significantly beyond it. However, two independent verification periods reveal highly positive reduction of error (RE) and coefficient of efficiency (CE) statistics. Less formal verification based on direct comparison with 14 European proxy‐based reconstructions further suggests relatively good agreement in the temporal occurrence of above/below mean late spring–early summer precipitation totals, especially in the 16th–17th centuries. The new MJJ precipitation reconstruction is restricted to inter‐annual and inter‐decadal variability, which is in line with our understanding of natural precipitation variability. Reconstruction reveals two long periods of low precipitation variability, in the 13th–14th centuries and 1630s–1850s. It also demonstrates that precipitation anomalies of larger amplitude and longer duration occurred in the earlier part of the last millennium than those found in the instrumental period. Negative trends in soil moisture content and gradual changes in annual precipitation distribution leading to higher extremity of precipitation regime may be responsible for the lower sensitivity of oaks to precipitation after the 1980s. The new reconstruction does not indicate any exceptional recent decline in MJJ precipitation.