Northern ecosystem productivity reduced by Rossby-wave-driven hot–dry conditions

Abstract

Large-scale quasi-stationary Rossby waves in the tropospheric jet stream favour spatially compounding hot–dry and cold–wet weather across the northern hemisphere. However, how this circumglobal circulation pattern affects northern hemisphere ecosystem productivity remains unexplored. Here, using satellite proxies of vegetation photosynthesis, we assess the impact of Rossby wave-7 events during which the jet stream exhibits seven peaks and troughs and tends to produce prolonged weather anomalies. Our results show organized declines in vegetation productivity in warm cores and enhancement in cold cores at northern mid-latitudes during summer Rossby wave-7 events. Mid-latitude biomes within warm cores become much more susceptible to water limitations, resulting from an increased exposure to compound hot–dry (or cold–wet) extremes and a nonlinear physiological response to compound stressors. Of the warm cores analysed, wave events elevate the climatic risk of productivity declines by a factor of 8.3, 6.2 and 4.0 over western Europe, western Asia and the western United States, respectively, due to hot–dry extremes. In particular, 32–44% of the warm anomalies and 52–88% of the dry anomalies fall within the range of warmer–drier conditions projected for 2081–2100 by state-of-the-art climate models under a medium emissions scenario. Therefore, the observed Rossby-wave-driven impacts provide an indication of how a warmer–drier future climate could reduce the carbon uptake capacity of northern hemisphere ecosystems.