Climate-driven reduction in biomass production of the Eurasian steppe coincides with nomadic migration during the first millennium CE - Feng Chen; Xiaoen Zhao; Weipeng Yue; Shijie Wang; Yong Zhang; Youping Chen; Mao Hu; Jan Esper; Ulf Büntgen; Fredrik Charpentier Ljungqvist; Amy E. Hessl; Max C. A. Torbenson; et al. (Proceedings of the National Academy of Sciences, 2026)