North Atlantic jet stream responses to AMOC tipping and global warming in regional climate simulations

Abstract. European weather variability is largely influenced by the position and intensity of the North Atlantic (NA) jet stream. Understanding how the NA jet may respond to global warming and an additional potential collapse of the Atlantic Meridional Overturning Circulation (AMOC) is therefore essential for assessing future European climate. Here, we investigate these changes using two fully coupled Earth System Models (MPI-ESM-HR and CESM1) together with high-resolution regional dynamical downscaling. Global warming is simulated by increasing atmospheric CO₂ until a global mean warming of 2 K is reached, while AMOC collapse is induced through freshwater hosing from this 2 K state. 

The regional simulations retain the main characteristics of the large-scale jet response simulated by the driving ESMs, while revealing regional modifications in both winter and summer that are more pronounced in summer. Under global warming, the response is highly model dependent, with an equatorward displacement of the winter jet in the MPI-driven simulations and a poleward displacement in the CESM-driven simulations. Following AMOC collapse, these contrasting responses persist, with the MPI-driven simulations retaining an equatorward-displaced jet and the CESM-driven simulations exhibiting a marked jet intensification.

These contrasting circulation changes arise from differences in the simulated AMOC response to global warming. MPI simulates substantially stronger AMOC weakening than CESM, leading to a more pronounced North Atlantic warming hole and stronger Arctic amplification. The resulting differences in sea surface temperature modify the meridional temperature gradients and baroclinicity, providing a physical explanation for the contrasting jet responses. Our results demonstrate that uncertainty in the simulated AMOC response propagates to regional atmospheric circulation and highlight the added value of regional dynamical downscaling for assessing the impacts of AMOC weakening and collapse on the North Atlantic jet stream.