PNNL

Abstract

Understanding historical hydroclimate change during the last millennium is of fundamental importance for forecasting and evaluating the regional hydrologic cycle and water security under global warming1-3. Here, we compared observations of tree-ring stable isotope ratios (d13C and d18O), tree-ring widths, lake sediment estimates of regional hydroclimate and glacier advance and retreat for northeastern QTP. Our composite isotope record and tree-ring widths indicated similar hydroclimate dynamics throughout the last millennium until the latter half of the 20th century, after which they diverged with the tree-ring widths indicating an unprecedented wet period whilst the isotopic results, sediment proxies and glaciers demonstrated a drying pattern. Atmospheric CO2 rise allowed increases in canopy-scale intrinsic water-use efficiency and growth, causing tree-ring widths to underestimate overwhelming the regional drying signal in the growth record. Precipitation inferred only rom tree-ring width may be overestimated due to atmospheric CO2 fertilization over the last century; this bias should be considered in tree-ring width reconstructions of palaeoclimate.