Human-Induced Westerly Jet Shifts Coordinate Terrestrial Productivity at the Hemispheric Scale

Previous studies have established how regional climate variability regulates local terrestrial gross primary productivity (GPP), yet the hemispheric-scale spatial organization of GPP, coordinated by coherent large-scale atmospheric circulation, has received far less attention. By integrating multi-source observations with numerical simulations, we demonstrate that anthropogenically driven shifts in the Northern Hemisphere westerlies fundamentally reorganize the spatial pattern of terrestrial GPP. Around the year 2000, the curvature of the westerlies reversed, transitioning from a southward to a northward bend over eastern Europe, Northeast Asia, and western North America, while exhibiting opposite changes over central Asia and central North America. The observed spatial pattern of GPP trends closely mirrors the GPP response to variations in westerly curvature. Sensitivity analyses using CESM1 large-ensemble simulations and single-forcing experiments identify greenhouse gas forcing as the dominant driver of these circulation changes, thereby reshaping GPP distributions. Under the RCP8.5 scenario, further intensification of westerly curvature shifts is projected to enhance GPP growth across northern Europe, Northeast Asia, and western North America, while suppressing productivity in southern Europe and central North America. Together, these results reveal a previously underappreciated pathway through which anthropogenic forcing influences terrestrial carbon uptake via large-scale atmospheric circulation, with important implications for projecting future carbon–climate feedback.