A global synthesis of climate indices reconstructed from historical archives

The field of historical climate reconstruction through documentary evidences has made significant advances in recent years, including a global synthesis of the index approach in climate reconstruction (Nash et al., 2021), a global documentary climate dataset (Burgdorf et al., 2023), and new perspectives to study historical climatology (White et al., 2022). Based on the progress, this study addresses two specific research questions: 1) What are the numerical structures and characteristics of the reconstructed climate index data across existing datasets from various continents? (2) Are these structures and characteristics reflective of long-term climatological traits in the regions, or are they controlled by other factors? By answering the questions, we collected climate index data from Africa, Australia, China, Europe, India and South America to analyze the data structure in each dataset. Each dataset’s structure was then compared against modern observational data, including ERA5 and the Global Historical Climatology Network (GHCN) monthly data, to identify correlations and asses credibility of the climate index data. The analysis involves spatial and temporal comparisons, statistical tests, and discussions on data quality and limitations.