Warming overwhelms CO2-driven drought mitigation in alpine vegetation on the Qinghai-Tibetan Plateau

Droughts have intensified under climate change, threatening ecosystem stability. While rising atmospheric CO2 concentrations may enhance vegetation drought resistance, the net effect remains uncertain amid concurrent warming. Here we combine ecological modeling with multi-source observations to investigate how CO2 and warming jointly regulate vegetation drought responses on the Qinghai-Tibetan Plateau, a sensitive alpine region exposed to escalating drought threats under changing precipitation regimes. Using factorial scenarios to isolate individual forcings, we show that 40-year CO2 rise mitigated drought-induced productivity losses by 5.7 ± 0.9% under constant temperature. However, in the presence of warming, rising CO2 intensifies drought stress by 5.2 ± 0.5%, reflecting increased plant water demand and disrupted regional water supply-demand balance. Permafrost areas experienced the strongest CO2-driven drought alleviation under constant temperature, but also the greatest warming-induced reversal. These findings reveal interacting CO2-warming impacts on alpine vegetation drought responses, highlighting ecological risks for the plateau and other permafrost-dominant regions under future warming. Rising CO₂ levels reduced drought stress on plants on the Qinghai–Tibetan Plateau over the past four decades, but this benefit is largely cancelled out by warming that increases plant water demand, as revealed by ecological modelling and multi-source observations from 1979 to 2018.