Projected weakening of Northern Hemisphere summertime high-latitude waveguide and teleconnection variability

Summertime high-latitude teleconnections shape persistent circulation anomalies and surface climate extremes across the Northern Hemisphere, yet their future evolution under anthropogenic warming remains poorly constrained. Using 31 CMIP6 models under SSP5-8.5, we examine projected changes in the high-latitude waveguide, teleconnection variability, and the resulting surface air temperature (SAT) response. The CMIP6 ensemble projects an ~20.3% weakening of the 250 hPa meridional potential vorticity (PV) gradient over 50°–80°N during 2050–2099 relative to 1965–2014. This weakening is driven primarily by the projected warming pattern itself: enhanced upper-tropospheric warming at low-to-mid latitudes together with vertically extensive Arctic warming reduces the meridional contrast in upper-tropospheric static stability. This weakened waveguide in turn supports less large-scale atmospheric variability. The interannual variability of the leading EOF1–3 teleconnection modes, represented by 250 hPa meridional winds, decreases by ~3.6%, with larger PV gradient reductions across models corresponding to larger declines in variability. This dynamical weakening does not, however, translate into weaker SAT variability. Teleconnection-related SAT variance increases because SAT anomalies become more sensitive to local circulation anomalies, although the physical processes underlying this enhanced sensitivity are not yet fully understood. These results show that the weakening of the high-latitude waveguide in a warmer world is accompanied by complex and diverse responses across multiple fields.