Direct vegetation response to recent CO2 rise shows limited effect on global streamflow

Global streamflow, crucial for ecology, agriculture, and human activities, can be influenced by elevated atmospheric CO₂ (eCO₂) though direct regulation of vegetation physiology and structure, which can either decrease or increase streamflow. Despite a 21.8% rise in CO₂ over 40 years, its impact on streamflow is not obvious and remains highly debated. Using a full differential approach at the catchment scale and an optimum finger approach globally, both constrained by observed streamflow, here, we find that vegetation responses to eCO₂ in 1981-2020 has limited impact on streamflow via direct regulation. The median eCO₂ contribution approaches zero across 1116 unimpacted catchments, and global streamflow changes cannot be solely attributed to eCO₂. These results offer key insights into the intricate dynamics of CO₂ and other factors shaping streamflow changes over the past four decades. Such understanding is vital for attributing current streamflow changes under eCO₂ conditions.